JP2002051551A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption by an input-side power circuit when a load is in standby state. SOLUTION: Alternating-current voltage outputted from an alternating-current power supply is rectified through an input-side rectifying circuit 4 and smoothed through an input-side smoothing circuit 6, thereby turning into input-side voltage. The input-side voltage is given to a switching element 9 that is on/off-controlled through a control circuit 10, through the primary winding 1a of a transformer 1. The voltage produced by on/off-control of the switching element 9 is given to an output rectifying means 55 through the transformer 1, and, after rectification, outputted to a load 45. The turn-on/off and stop of the switching element 9 are controlled based on the output voltage outputted to the load 45. If it is detected that the load 45 is in standby state, the smoothing capacity of an input-side smoothing circuit 7 is reduced, and the switching element 9 is on/off- controlled only when the input-side voltage falls below a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for converting an AC current from an AC power supply into a DC current and outputting the DC current to loads such as home appliances and electronic equipment. The present invention relates to a switching power supply device capable of reducing power consumption on an input side in a load fluctuation state or a standby state.

[0002]

2. Description of the Related Art FIG. 28 is a circuit diagram showing an example of a conventional switching power supply. The switching power supply device 85 includes an input-side power supply circuit 80 that transforms a voltage output from an AC power supply 2 such as a commercial power supply by a transformer 1 and a load 4 such as an electronic device that transforms the voltage transformed by the transformer 1.
5 and an output-side power supply circuit 81 for outputting the signal to the output side.

An input side power supply circuit 80 includes an input side rectifier circuit 4 for rectifying an AC voltage input from an AC power supply 2 such as a commercial power supply via a filter 3 and a smoothing of an output voltage of the input side rectifier circuit 4. An input-side smoothing circuit 73 is provided, and a DC input-side voltage Vin output from an output terminal of the input-side smoothing circuit 73 is applied to one end of the primary winding 1 a of the transformer 1.

The other end of the primary winding 1a of the transformer 1 is connected to a high potential side terminal of a switching element 9. The switching element 9 performs switching control (on / off control) of the DC input side voltage Vin applied to the high potential side terminal. The control terminal of the switching element 9 is connected to the GATE terminal of the control circuit 77, and the switching operation (on / off operation) of the switching element 9 is controlled by the control circuit 77. The low potential side terminal of the switching element 9 is connected to the GND /
It is connected to the SOURCE terminal.

The primary winding 1a of the transformer 1 is connected in parallel with a snubber circuit 8 for preventing a voltage higher than the withstand voltage between DRAIN and SOURCE of the switching element 9 from being applied during the switching operation by the switching element 9. Have been.

The control circuit 77 for controlling the switching operation of the switching element 9 includes a GATE terminal to which the control terminal of the switching element 9 is connected, a DRAIN terminal to which the high-potential side terminal of the switching element is connected, and a control circuit 77. And a FB terminal to which a feedback signal from the output side power supply circuit 81 is input.
/ SOURCE terminal.

The switching element 9 is connected to the DRAIN terminal.
Is supplied to the high-potential side terminal of the control circuit 77, and the current is supplied to the overcurrent protection means provided in the control circuit 77. The overcurrent protection means limits the current supplied to the high potential side terminal of the switching element 9 to a predetermined upper limit value ILIMIT or less.

A control circuit power supply capacitor 11 is connected to the BP terminal of the control circuit 77, and the power supply voltage VBP of the control circuit 77 is held at a predetermined reference voltage VBP0 by the control circuit power supply capacitor 11. It has become so.

The FB terminal of the control circuit 77 is connected to a photodiode 14b operated by a feedback signal from the output power supply circuit 81. This photodiode 1
4b functions as a light receiving portion of a photocoupler constituting a feedback circuit from the output side power supply circuit 81 to the input side power supply circuit 80.

The GND / SOURCE terminal of the control circuit 77 is set to the ground level, and the GND / SOURCE terminal is
The input side rectifier circuit 4 and the input side smoothing circuit 7 are connected to the RCE terminal.
3. The control circuit power supply capacitor 11 and the ground terminal of the photodiode 14b are respectively connected, and the low potential side terminal of the switching element 9 is also connected.

The output-side power supply circuit 81 is provided with an output-side rectifier circuit 12 connected to the secondary winding 1b of the transformer 1.
Is rectified. The output voltage of the output-side rectifier circuit 12 is provided to the output-side smoothing circuit 13, and the output-side smoothing circuit 13 smoothes the output voltage of the output-side rectifier circuit 12 and outputs the smoothed output voltage. The output-side smoothing circuit 13 outputs a DC output voltage Vout, which is the output of the output-side power supply circuit 81, and supplies the output-side main terminal (VOUT) 17a of the output-side power supply circuit. The output side main terminal 17a and the output side sub terminal (RETUR)
N) 17b, a load 45 such as an electronic device is connected, and a voltage Vo output from the output side main terminal 17a is connected.
The load 45 is driven by ut.

The output side power supply circuit 81 has an output voltage detection circuit 14 for detecting an output voltage Vout in parallel with the load 45 connected to the output side main terminal 17a and the output side sub-terminal 17b of the output side smoothing circuit 13. Is provided. The output voltage detection circuit 14 includes a light emitting element 14a constituting a photocoupler together with a photodiode 14b provided in the input side power supply circuit 80.
When ut rises above the reference voltage Vout0, the output voltage detection circuit 14 turns on the light emitting element 14a. When the light emitting element 14a is turned on, the light emitting element 14a
Is emitted as a feedback signal to the photodiode 14b provided in the input-side power supply circuit 80.

FIGS. 29A to 29H are timing charts showing the operation of the switching power supply 85 having such a configuration. FIG. 29A shows the input-side voltage Vin smoothed and output by the input-side smoothing circuit 73. FIG. 29B shows a current IDRAIN flowing when the switching element 9 is turned on. FIG. 29 (c)
The state of the load 45 corresponding to the drain current IDRAIN of the switching element 9 is schematically shown.

FIGS. 29 (d) to 29 (h) correspond to FIGS.
This is an enlarged view of the time axis of IDRAIN shown in FIG. 9 (b). FIG. 29D shows the voltage VDRAIN of the high potential side terminal of the switching element 9,
FIG. 29E shows the power supply voltage VBP which is the voltage of the BP terminal of the control circuit 77. Note that VBP0 in FIG. 29E is the power supply voltage VBP in the control circuit 77.
Of the reference voltage. FIG.
The current IDRA flowing through the switching element 9 shown in FIG.
It is an enlarged view of IN. FIG. 29 (g) shows the output voltage Vout of the output side power supply circuit 81, and Vout0 in FIG. 29 (g) is a reference voltage set by the output voltage detection circuit 14. FIG. 29H shows the current I flowing from the FB terminal of the control circuit 77 to the GND / SOURCE terminal.
FB is shown.

The operation of the switching power supply 85 shown in FIG. 28 will be described with reference to the time chart of FIG.
The AC voltage obtained by the AC power supply 2 is rectified by the input-side rectifier circuit 4 as shown in FIG. 29A, and is supplied to the input-side smoothing circuit 73 as the input-side rectified voltage Vr. Input-side rectified voltage V applied to input-side smoothing circuit 73
r is smoothed by the input side smoothing circuit 73 to be a DC input side voltage Vin, and the input side voltage Vin is
It is provided to the primary winding 1a of the transformer 1.

The input side voltage Vin applied to the primary winding 1a of the transformer 1 passes through the DRAIN terminal of the control circuit 77, and is charged from the BP terminal to the control circuit power supply capacitor 11. Then, when the power supply voltage VBP at the BP terminal reaches the reference voltage VBP0, the control circuit 77 is activated. Thus, the on / off control of the switching element 9 is started.

Note that while the switching element 9 is on / off controlled by the control circuit 77, the power supply voltage VBP
Is lower than the reference voltage VBP0, a current is charged from the BP terminal to the control circuit power supply capacitor 11 through the DRAIN terminal of the control circuit 77, and the power supply voltage VBP is controlled to be equal to or higher than the reference voltage VBP0.

When the switching element 9 connected to the primary winding 1a is intermittently turned on and off, an input-side voltage Vi is generated in the primary winding 1a of the transformer 1 and the secondary winding 1b of the transformer 1 is generated. The output voltage Vo is generated by the input voltage Vi generated in the primary winding 1a. Secondary winding 1
The output side voltage Vo generated at b is rectified by the output side rectifier circuit 12 and then smoothed by the output side smoothing circuit 12. As a result, the output side main terminal 17a of the output side power supply 81 is connected to the DC output voltage Vou shown in FIG.
t is output. This output voltage Vout is applied to the load 45 connected to the output-side main terminal 17a, and the load 45
Is driven.

The output voltage detection circuit 14 detects the output voltage Vout output from the output side smoothing circuit 12,
When the load 45 enters the load fluctuation state,
As shown in (g), a predetermined reference voltage V
When a voltage equal to or more than out0 is detected by the output voltage detection circuit 14, the light emitting element 14a provided in the output voltage detection circuit 14 is turned on, and the photodiode 14b provided in the input side power supply circuit 80 is turned on. .

When the photodiode 14b connected to the FB terminal of the control circuit 77 is turned on, the switching operation, which is the intermittent on / off control of the switching element 9 by the control circuit 77, is stopped. When the on / off control of the switching element 9 is stopped, the output voltage Vout of the output-side power supply circuit 81 gradually decreases to a predetermined reference voltage Vout.
When the value becomes 0 or less, the light emitting element 14a provided in the output voltage detection circuit 14 turns off, and the photodiode 14b also turns off. Accordingly, the control circuit 77 restarts the on / off control of the switching element 9 and the output voltage Vout of the output side power supply circuit 81 increases.

While the switching operation of the switching element 9 is being performed, the on-duty DC (see FIG. 29), which is the time width during which the switching element 9 is in the ON state, depends on the inductance of the primary winding 1a of the transformer 1. The value is set based on the value.
7 is smaller than the maximum on-duty MAXDC, which is the maximum on-time width set by 7.

The control circuit 77 uses the built-in overcurrent protection means to reduce the drain current IDRAIN flowing when the switching element 9 is turned on to a predetermined upper limit value ILIMIT.
Control so that

In such a switching power supply device 85, when the load 45 driven by the output voltage Vout is in a heavy load state, the output voltage Vout is substantially constant without substantially increasing. The output voltage Vout of the circuit 81 is set to a predetermined reference voltage Vout0.
Hardly ever rises. As a result, the light emitting element 14a provided in the output voltage detecting circuit 14 is turned on, and the photodiode 14b is hardly turned on. Therefore, the control circuit 77 almost stops the on / off control of the switching element 9. Not, but continuously.

On the other hand, when the load 45 is in the load fluctuation state, a period occurs in which the output voltage Vout is equal to or higher than the reference voltage Vout0 (Vout ≧ Vout0). And
As the load state of the load 45 is reduced, that is, as it approaches the standby state, the period of Vout ≧ Vout0 becomes longer, and the time during which the light emitting element 14a of the output voltage detection circuit 14 is turned on, that is, the photodiode 14b is turned on. The time gets longer. Therefore, as the load state of the load 45 is reduced, the time during which the control circuit 77 stops the on / off control of the switching element 9 becomes longer. As a result, the load 45
As the load state is reduced, the driving time of the switching element 9 by the control circuit 77 is shortened, and the power consumption in the control circuit 77 is reduced.

As described above, the control circuit 77 compares the voltage change (ripple voltage) of the output voltage Vout with the reference voltage Vout0 by the output voltage detection circuit 14, and performs on / off control of the switching element 9 and on / off control thereof. Is controlled so that the output voltage Vout becomes the reference voltage Vout0.
As the load state of the control circuit 77 is reduced, the power consumption of the control circuit 77 is reduced.

FIG. 30 is a circuit diagram showing another example of a conventional switching power supply device. In this switching power supply device 85, an auxiliary winding 1c is provided in parallel with the primary winding 1a of the input side power supply circuit 80 provided on the input side of the transformer 1 in an insulated state. One end of the auxiliary winding 1c is connected to the low potential side terminal of the switching element 9, and the other end is connected to the diode 24. The diode 24 is connected in series with a photodiode 14b constituting a light receiving portion of a photocoupler. The output of the photodiode 14b is supplied to a CONTROL terminal of a control circuit 77 to which the control circuit power supply capacitor 11 is connected. Have been.

The control circuit power supply capacitor 11 connected to the CONTROL terminal of the control circuit 77 is charged by a current flowing through the auxiliary winding 1c of the transformer 1 and the diode 24 when the photodiode 14b is turned on. The photodiode 14b turns on the light emitting element 14a when the output voltage detection circuit 14 provided in the output side power supply circuit 81 detects that the output voltage Vout is equal to or higher than the reference voltage Vout0, and
Turn on.

The control circuit 77 has a DRAIN terminal connected to the high potential side terminal of the switching element 9, a CONTROL terminal connected to the control circuit power supply capacitor 11, a GATE terminal connected to the switching element 9,
GND to which the low potential side terminal of the switching element 9 is connected
/ SOURCE terminal is provided. GND / SOU
The RCE terminal is set to the ground potential. Other configurations are shown in FIG.
8 has the same configuration as the conventional switching power supply device 85 shown in FIG.

FIG. 31 is a time chart showing the operation of the switching power supply device shown in FIG. FIG. 31 (a)
Represents the input side voltage Vin, and FIG.
5 shows a drain current IDRAIN of the switching element 9. FIG. 31C schematically shows the output-side load state. FIGS. 31 (d) to 31 (g) are enlarged views of the time axis of FIG. 31 (a). FIG. 31 (d) shows the voltage of the high potential side terminal of the switching element 9. FIG. 31 (e) shows VDRAIN.
It shows the voltage Vc of the CONTROL terminal of the control circuit 77. FIG. 31F shows the current ID of the switching element 9.
FIG. 31 (g) shows the output voltage Vo.
ut.

The operation of the switching power supply 85 shown in FIG. 30 will be described with reference to the time chart shown in FIG. In this switching power supply device 85, the on-duty DC which is the time when the switching element 9 is turned on is set based on the CONTROL terminal voltage Vc of the control circuit 77. As shown in FIG. 31 (e), CONTROL
With respect to the terminal voltage Vc, the lower limit value Vc1 and the upper limit value Vc
c2 is set.

As shown in FIGS. 31 (e) and 31 (g), the voltage of the control circuit power supply capacitor 11, CO
When the power supply voltage Vc of the NTROL terminal is equal to or lower than the lower limit value Vc1 (Vc ≦ Vc1), the on-duty DC of the switching element 9 becomes the maximum on-duty DC.
max and the CONTROL terminal voltage Vc is equal to or higher than the lower limit value Vc1 and equal to or lower than the upper limit value Vc2 (Vc
For 1 ≦ Vc ≦ Vc2), the on-duty DC of the switching element 9 is controlled between the maximum duty DCmax and the minimum duty DCmin. Furthermore, CONT
When the voltage Vc of the ROL terminal is equal to or higher than the upper limit value Vc2 (V
For c2 ≦ Vc), the on-duty DC of the switching element 9 is controlled to the minimum duty DCmin.

In such a switching power supply device 85, when the output voltage Vout of the output side power supply circuit 81 is equal to or higher than a predetermined reference voltage Vout0 (Vout ≧ Vout0), the light emitting element 14 provided in the output voltage detection circuit 14 is provided.
a is on and the photodiode 14b is on,
Power is supplied from the auxiliary winding 1c to the control circuit power supply capacitor 11. When the load 45 is in a heavy load state, Vout ≧
The period during which Vout0 is attained is short, the amount of current supplied to the control circuit power supply capacitor 11 is reduced, and the power supply voltage Vc of the CONTROL terminal is lower than the lower limit Vc1 (V
c ≦ Vc1) becomes longer. As a result, the on-duty DC of the switching element 9 becomes the maximum on-duty DC.
It is controlled to be max, and the ON time of the switching element 9 is prolonged, so that power is reliably supplied to the load 45 in the heavy load state.

In the load fluctuation state, the output voltage Vout is higher than the reference voltage Vout0 (V
(out ≧ Vout0) becomes longer, and as the load state of the load 45 decreases and approaches the standby state, Vout ≧ Vout ≧
The period of Vout0 becomes even longer. Therefore, the time during which the light emitting element 14a of the output voltage detection circuit 14 is turned on, that is, the time during which the photodiode 14b is turned on, becomes longer.

As the time during which the photodiode 14b is turned on becomes longer, the current supply time to the control circuit power supply capacitor 11 becomes longer, and the power supply voltage Vc at the CONTROL terminal in the control circuit 77 to which the control circuit power supply capacitor 11 is connected. Rises. Power supply voltage Vc is lower limit value Vc1
When the duty ratio is between Vc2 and the upper limit value Vc2 (Vc1 ≦ Vc ≦ Vc2), the on-duty DC of the switching element 9 is controlled between the maximum duty DCmax and the minimum duty DCmin. As a result, the ON time of the switching element 9 is shortened, and the voltage to the load 45 is reduced.

Then, when the load 45 approaches the standby state,
The output voltage Vout is equal to or higher than the reference voltage Vout0 (Vout
≧ Vout0), the output voltage detection circuit 1
The time during which the light emitting element 14a of No. 4 is turned on, that is, the time during which the photodiode 14b is turned on, is further increased. Thus, the time for supplying the current to the control circuit power supply capacitor 11 is further increased. When the power supply voltage Vc of the CONTROL terminal to which the control circuit power supply capacitor 11 is connected rises above the upper limit value Vc2 (Vc2 ≦ V
c), the on-duty DC of the switching element 9 is controlled to the minimum duty DCmin. As a result, the ON time of the switching element 9 is further shortened, and the voltage to the load 45 is further reduced.

[0036]

In recent years, in order to protect the global environment, there has been a demand for energy saving. In such a switching power supply device 85, further lower power consumption and higher efficiency have been demanded. I have. The power consumption of input side power supply circuit 80 in switching power supply device 85 shown in FIGS. 28 and 30 is the sum of power Winl consumed by control circuit 77 and power Win2 consumed by switching element 9 (= Win1 + Win).
2). Power consumption Win2 of switching element 9
Is the input-side voltage Vi output from the input-side smoothing circuit 73.
n and the current IDRA flowing through the switching element 9
The power consumption Winl of the control circuit 77 is proportional to IN.
(Win2 >> Win)
1).

Therefore, in order to further reduce the power consumption of the input-side power supply circuit 80 when the load 45 is in the load fluctuation state or the standby state, it is necessary to reduce the power consumption Winl of the control circuit 77. It is important to reduce the power consumption Win2 of the element 9.

However, in the switching power supply device 85 shown in FIGS. 28 and 30, the load 45 reduces the power consumption Win2 of the switching element 9 in the load fluctuation state or in the standby state, particularly in the standby state, so that the input side power supply circuit There is a problem that it is not easy to further reduce the power consumption of the 80.

An object of the present invention is to solve such a problem. An object of the present invention is to reliably reduce power consumption in an input-side power supply circuit when a load on an output side is in a load fluctuation state or a standby state. It is an object of the present invention to provide a switching power supply device that can perform the switching.

[0040]

A switching power supply device according to the present invention includes an input rectifier circuit for rectifying an AC voltage output from an AC power supply, and an input side smoothing circuit for smoothing an output voltage of the input rectifier circuit. An input voltage detection circuit that detects a DC input voltage output from the input smoothing circuit;
A switching element to which the input-side voltage is applied, an input-side power supply circuit provided with a control circuit for controlling on / off of the switching element, and a rectified and smoothed DC voltage formed by on-off control of the switching element An output-side power supply circuit provided with an output direct-current conversion means for outputting a voltage to a predetermined load, wherein the output power supply circuit detects that the load is in a load fluctuation state or a standby state. A side load state detection circuit, and when the output side load state detection circuit detects that the load is in a standby state, the smoothing capacity of the input side smoothing circuit is reduced. Only when the input side voltage output from the input side smoothing circuit is lower than a predetermined value, on / off control of the switching element is performed.

A primary winding of a transformer is provided between the input-side smoothing circuit of the input-side power supply circuit and the switching element, and the output of the secondary winding of the transformer is supplied to the output DC converting means. I have.

The transformer is provided with a switch for reducing an input-side inductance when an output voltage output from the output DC converter to the load in a standby state falls below a predetermined reference voltage. I have.

The input side smoothing circuit is provided with a smoothing capacity changeover switch for reducing the smoothing capacity, and the smoothing capacity changeover switch is switched by the output side load state detecting circuit.

The smoothing capacity changeover switch is MOSFE
T.

An output voltage output from the output DC conversion means is detected by an output voltage detection circuit provided in the output side power supply circuit, and a detection result of the output voltage detection circuit is used as a feedback signal. The signal is fed back to the input side power supply circuit by the circuit.

The on / off control of the switching element is as follows:
The operation is stopped based on the detection result of the output voltage detection circuit.

The period during which the on / off control of the switching element is stopped changes continuously based on the change in the output voltage detected by the output voltage detection circuit.

The feedback circuit is configured to use an optical signal.

The feedback circuit is constituted by a photocoupler.

The output voltage detection circuit is constituted by a Zener diode.

The control circuit is provided with a control circuit power supply capacitor used as a power supply for the control circuit.

The control circuit and the switching element are:
A semiconductor device provided on the same substrate, wherein the semiconductor device includes a pair of terminals to which a high potential terminal and a low potential terminal of a switching element are connected, respectively, A terminal to which a detection result is input, a terminal to which the control circuit power supply capacitor is connected, and a terminal to which a detection result of a DC input side voltage output from the input side smoothing circuit is input. It has two external terminals.

The input side power supply circuit is provided with a snubber circuit for absorbing noise generated by the on / off control of the switching element.

The control circuit is provided with an overcurrent protection means for stopping the on / off control of the switching element due to an overcurrent to the control circuit.

The control circuit is provided with overheat protection means for stopping on / off control of the switching element when the control circuit is overheated.

The output side power supply circuit outputs a DC voltage having an absolute value lower than the DC voltage output from the input side smoothing circuit.

The reference potential of the power supply voltage of the control circuit is higher than the reference value of the output voltage from the output side power supply circuit, and the output voltage is detected irrespective of whether the switching element is on or off.

The reference potential of the power supply voltage of the control circuit is higher than the reference value of the output voltage from the output side power supply circuit, and the output voltage is detected while the switching element is off. You.

The input side voltage output from the input side smoothing circuit is 100 V or more, and the absolute value of the DC voltage output from the output side power supply circuit is 25 V or less.

The DC voltage output from the output side power supply circuit has a positive polarity or a negative polarity.

The control circuit is provided with a control circuit power supply capacitor serving as a power supply for the control circuit, and a DC voltage output from the output side power supply circuit is provided in the output side power supply circuit. An output terminal is detected by an output voltage detection circuit, and an output terminal of the output side power supply circuit is connected to the control circuit power supply capacitor.

The ON time in the ON / OFF control of the switching element is controlled based on the output voltage output from the output DC converting means.

The input side power supply circuit is provided with an auxiliary winding to which energy is applied via the transformer, and the control circuit is provided with a control circuit power supply in which an output from the auxiliary winding is rectified and charged. A capacitor is provided as a power supply for the control circuit, and a current supplied from the auxiliary winding to the control circuit power supply capacitor is controlled based on an output voltage output from the output DC converting means.

The output voltage output from the output DC conversion means is detected by an output voltage detection circuit provided in the output side power supply circuit, and the detection result of the output voltage detection circuit is used as a feedback signal. The signal is fed back to the input side power supply circuit by the circuit.

The feedback circuit is configured to use an optical signal.

The output side load state detection circuit detects the load fluctuation state or the standby state of the load based on the output voltage output from the output of the output DC conversion means to the load. Provided in the circuit.

The output side load state detection circuit is provided in the input side power supply circuit so as to detect a load fluctuation state or a standby state of the load based on a voltage of the control circuit power supply capacitor.

The control circuit and the switching element include:
A semiconductor device provided on the same substrate, wherein the semiconductor device is connected to a pair of terminals to which a high-potential side terminal and a low-potential side terminal of a switching element are connected, respectively, and the control circuit power supply capacitor. , A terminal for outputting a detection result of the output side load state detection circuit, and a terminal for receiving a detection result of the input voltage detection circuit.

[0069]

<First Embodiment> FIG. 1 is a circuit diagram showing an example of a switching power supply according to an embodiment of the present invention. The switching power supply device 70 includes an input-side power supply circuit 50 that outputs a DC voltage from an input AC current.
And a transformer 1 for transforming a DC voltage output from the input-side power supply circuit 50, and an output-side power supply circuit 60 for outputting the voltage transformed by the transformer 1 to a load 45 such as an electronic device.
And

The input-side power supply circuit 50 is provided with an input-side rectifier circuit 4 to which an AC voltage output from an AC power supply 2 such as a commercial power supply is applied through a filter 3. The rectified AC voltage is supplied to the input-side smoothing circuit 5 as a DC input-side rectified voltage Vr.

The input side smoothing circuit 5 smoothes the applied DC input side rectified voltage Vr to obtain an input side voltage Vin,
Output to the primary winding 1a of the transformer 1. The input side smoothing circuit 5 is provided with a smoothing capacity changeover switch 6.
The smoothing capacity of the input-side smoothing circuit 5 is reduced by switching the smoothing capacity switch 6.
When the smoothing capacity of the input side smoothing circuit 5 is reduced, the input side voltage Vin output from the input side smoothing circuit 5 is reduced.

The input side smoothing circuit 5 is connected in parallel with an input voltage detecting circuit 7 for detecting a DC input side voltage Vin output from the input side smoothing circuit 5.

Transformer 1 supplied with input side voltage Vin
The primary winding 1a is connected to a high potential side terminal of a switching element 9 constituted by an N-channel MOS transistor. The control terminal of the switching element 9 is connected to the GATE terminal of the control circuit 10 so that the control circuit 10 performs on / off control (switching control). The low potential side terminal of the switching element 9 is connected to the GND / SOURCE terminal of the control circuit 10.

The switching element 9 is turned on and off by the output of the GATE terminal of the control circuit 10 to apply a pulsating voltage to the primary winding 1a of the transformer 1. A pulsating voltage is generated in the secondary winding 1b.

A snubber circuit 8 is connected in parallel to the primary winding 1a of the transformer 1. The snubber circuit 8 operates between the DRAIN-SOURCE of the switching element 9 and the DRAI during the ON / OFF control of the switching element 9.
This prevents a voltage higher than the breakdown voltage between N-SOURCE from being applied.

A DC voltage applied from the primary winding 1a of the transformer 1 to the high potential side terminal of the switching element 9 is applied to the DRAIN terminal of the control circuit 10 for controlling the switching element 9 to be turned on and off. The low potential side terminal of the switching element 9 is connected to GND / SOURCE of the control circuit 10.
Terminal, and this GND / SOURCE terminal is grounded.

An input voltage detection circuit 7 for detecting an input side voltage Vin is connected to a VIN terminal of the control circuit 10. An output from the input voltage detection circuit 7 is supplied to the control circuit 1.
0 VIN terminal.

The BP terminal of the control circuit 10 and GND / SOU
The power supply voltage VBP of the control circuit 10 is connected to the RCE terminal.
Is connected. Further, a photodiode 14b constituting a light receiving portion of the photocoupler is connected between the FB terminal and the GND / SOURCE terminal. When the photodiode 14b is turned on, the FB terminal is set to the ground potential.
The control circuit 10 stops the on / off control of the switching element 9 by setting the FB terminal to the ground potential.

Photodiode 1 connected to FB terminal
4b constitutes a light receiving portion of a photocoupler constituting a feedback circuit from the output side power supply circuit 60 to the input side power supply circuit 50.

Inside the control circuit 10, there is provided an overcurrent protection means for controlling the drain current IDRAIN of the switching element 9 to a predetermined upper limit value ILIMIT or less when the switching element 9 is turned on.

The output power supply circuit 60 includes an output rectifier circuit 12 for rectifying the output voltage Vo of the pulsating current generated in the secondary winding 1 b of the transformer 1, and a DC voltage output from the output rectifier circuit 12. And an output-side smoothing circuit 13 for smoothing the DC output voltage to obtain a DC output voltage Vout. Output voltage Vout of output side smoothing circuit 13
Are supplied to an output-side main terminal (VOUT) 17a constituting an output terminal of the output-side power supply circuit 60. A load 45 such as an electronic device is connected between the output-side main terminal 17a and the output-side sub-terminal (RETURN) 17b, and the output voltage Vout output from the output-side main terminal 17a is applied to the load 4.
5 given.

Output-side main terminal 17a and output-side sub-terminal 17b
The output voltage detection circuit 14 detects that the load 45 is in a load fluctuation state based on the output voltage Vout applied to the load 45, and the output side detects that the load 45 is in a standby state. Load state detection circuits 15 are provided in parallel with each other.

The output voltage detection circuit 14 is constituted by, for example, a zener diode. The output voltage detection circuit 14 is provided with a light emitting element 14a of a photocoupler. The light emitting element 14a is connected in series with, for example, a Zener diode that constitutes the output voltage detection circuit 14. The light emitting element 14a is configured such that when the load 45 is in a load fluctuating state, the output voltage Vout applied to the load 45 is When the output voltage detection circuit 14 detects that the output voltage has risen above the predetermined reference voltage Vout0, the output voltage detection circuit 14 is turned on and irradiates light to the photodiode 14b of the photocoupler provided in the control circuit 10 of the input-side power supply circuit 50. , The photodiode 14b is turned on. When the photodiode 14b is turned on, the control circuit 10
FB terminal is grounded, and the control circuit 10 stops the on / off control of the switching element 9.

As described above, the light emitting element 14 of the photocoupler
a and the photodiode 14 b are connected to the output side power supply circuit 6.
0 that the output voltage Vout is higher than the reference voltage Vout0.
Is returned in an electrically insulated state.

The output-side load state detection circuit 15 connected in parallel to the load 45 includes a load 4 connected to the output terminal.
5 detects, based on the output voltage Vout, that the power supply 5 is in a standby state requiring little power, and detects that the load 45 is in a standby state. A low-level signal for switching the smoothing capacitance switch 6 is output to the smoothing capacitance switch 6. Thereby, the smoothing capacity changeover switch 6 is switched, the smoothing capacity of the input side smoothing circuit 5 is reduced, and the input side voltage Vin output from the input side smoothing circuit 5 is reduced.

The switching power supply 7 having such a configuration
The operation of 0 will be described based on the time chart shown in FIG. FIG. 2A shows an input-side voltage Vin output from the input-side smoothing circuit 5, and Vin0 in FIG.
Is a reference voltage when the control circuit 10 starts the on / off operation of the switching element when the load 45 is in a standby state requiring almost no power, and the input side voltage Vin is lower than the reference voltage Vin0. In this case, the control circuit 10 can turn on and off the switching elements.

FIG. 2B shows the drain current IDRAIN of the switching element 9 and FIG. 2C shows the drain current IDRAIN of the switching element 9 and the load 4.
5 is schematically shown.

FIGS. 2D to 2I respectively correspond to FIGS.
3A and 3B are enlarged views of the time axis. FIG. 2D shows an output signal from the output-side load state detection circuit 15. When the load 45 is in a heavy load state or a load fluctuation state, the output-side load state detection circuit 15 outputs a high-level signal (H). Is output, and when the load 45 is in the standby state, the output side load state detection circuit 15 outputs a low level signal (L).

FIG. 2E shows the voltage VDRAIN at the high-potential side terminal of the switching element 9, and FIG.
Indicates a voltage VBP at the BP terminal of the control circuit 10. FIG. 2G shows the current IDRAIN flowing through the switching element 9, and FIG. 2H shows the output voltage Vout of the output-side power supply circuit 60. FIG.
(I): GND / SOU from the FB terminal of the control circuit 10
The current IFB flowing to the RCE terminal is shown.

In the switching power supply 70 shown in FIG. 1, an AC voltage output from the AC power supply 2 is converted into a DC input side voltage Vin by the filter 3, the input side rectifier circuit 4 and the input side smoothing circuit 5, It is provided to the primary winding 1a of the transformer 1.

The input-side voltage Vin applied to the primary winding 1a of the transformer 1 passes through the control circuit 10 from the DRAIN terminal of the control circuit 10, and is charged in the control circuit power supply capacitor 11 connected to the BP terminal. You. Then, the power supply voltage VBP of the control circuit power supply capacitor 11 becomes equal to the reference voltage V.
When BP0 is reached, the control circuit 10 is started, and the on / off control of the switching element 9 is started.

When the switching element 9 connected to the primary winding 1a is intermittently turned on and off, an input voltage Vi, which is a pulsating voltage, is generated in the primary winding 1a of the transformer 1, and The output voltage Vo of the pulsating current is applied to the secondary winding 1b by the input voltage Vi generated in the primary winding 1a.
Occurs. The output-side voltage Vo of the pulsating current generated in the secondary winding 1b is rectified by the output-side rectifier circuit 12 and further smoothed by the output-side smoothing circuit 13, thereby becoming a DC output voltage Vout. Output main terminal 1
7a. And this output voltage Vout is
It is provided to a load 45 connected to the output side main terminal 17a.

The load 45 requires almost no power in the standby state, and the required power increases when the load fluctuates, and a larger load requires a larger amount of power.

The output voltage detection circuit 14 outputs the output voltage Vo output from the output side smoothing circuit 13 and applied to the load 45.
ut is detected. Output voltage Vou for load 45
In the heavy load state in which the load 45 requires a large amount of power, there is almost no period during which t is higher than a predetermined reference voltage Vout0. Therefore, the light emitting element 14a provided in the output voltage detection circuit 14 is hardly turned on, and the control circuit 10 continuously performs the on / off control of the switching element 9. This allows
As shown in FIGS. 2B and 2C, the drain current IDRAIN is supplied to the switching element 9 almost continuously.

On the other hand, when the load 45 is in the load fluctuation state and the power consumption by the load 45 is reduced, the output voltage Vout becomes the predetermined reference voltage Vout.
A period in which the period is higher than t0 occurs. In such a state, the light emitting element 14a of the photocoupler is turned on, and the photodiode 1 connected to the FB terminal of the control circuit 10 is turned on.
4b is also turned on. As a result, F
The B terminal is forcibly set to the ground potential, and the control circuit 10 stops the on / off control of the switching element 9.

When the on / off control of the switching element 9 by the control circuit 10 is stopped, the output voltage Vout of the output side power supply circuit 60 gradually decreases. Then, the output voltage Vout of the output side power supply circuit 60 is set to a predetermined reference voltage Vout0.
When the light emission element 14a of the output voltage detection circuit 14
Is turned off, and the photodiode 14b is also turned off. As a result, the control circuit 10 is restarted, and the on / off control of the switching element 9 is restarted.

Output voltage Vout applied to load 45
Is such that as the load 45 approaches the standby state, the reference voltage Vout
The period that is higher than 0 becomes longer. Therefore, as the load 45 approaches the standby state, the time during which the photodiode 14b provided in the output voltage detection circuit 14 is turned on becomes longer, and the time during which the control circuit 10 stops the on / off control of the switching element 9 becomes longer. Thus, the control circuit 10
The stop time of the on / off control of the switching element 9 is continuously changed with respect to the change of the output voltage Vout. As the period during which the output voltage Vout becomes higher than the reference voltage Vout0 becomes longer, the on / off control of the switching element 9 becomes longer. The stoppage time of is longer.

The control circuit 10 compares the voltage change (ripple voltage) of the output voltage Vout supplied to the load 45 with the reference voltage Vout0, and controls the on / off control of the switching element 9 and the stop of the on / off control. Is repeated, the output voltage Vout becomes the reference voltage Vout.
It is controlled to be 0. In addition, as the load 45 approaches the heavy load state, the on-off control stop time of the switching element 9 is shortened, and as the load element 45 approaches the standby state, the on-off control stop time is extended. And the power consumption by the control circuit 10 is reduced.

When the current IDRAIN (shown in FIG. 2 (g)) flowing when the switching element 9 is turned on reaches a predetermined upper limit value ILIMIT, the control circuit 10 The ON operation of the switching element 9 is stopped by the current protection means. As a result, there is no possibility that the drain current IDRAIN flowing when the switching element 9 is turned on rises above the predetermined upper limit value ILIMIT, and an overcurrent is prevented from flowing through the control circuit 10.

When the load 45 enters the standby state, the period during which the output voltage Vout for the load 45 is higher than the reference voltage Vout0 is further extended. As a result, the output-side load state detection circuit 15 of the output-side power supply circuit 60 is configured as shown in FIG.
As shown in (1), the low-level signal is output to the smoothing capacitance changeover switch 6 provided in the input side smoothing circuit 5, and the smoothing capacitance changeover switch 6 is switched. When the smoothing capacitance switch 6 is switched, the smoothing capacitance of the input-side smoothing circuit 5 is reduced, and the input-side voltage Vin output from the input-side smoothing circuit 5 is reduced as shown in FIG. .

The input side voltage Vin output from the input side smoothing circuit 5 is detected by the input voltage detecting circuit 7, and the input side voltage Vin reduced from the input side smoothing circuit 5 is used as the reference voltage. When the input voltage is lower than Vin0, the input voltage detection circuit 7
A predetermined signal is output to the zero Vin terminal. This allows
The switching circuit 9 is turned on and off by the control circuit 10 based on the output voltage Vout.

Therefore, when the load 45 is in the standby state, only when the input side voltage Vin output from the input side smoothing circuit 5 in a reduced state becomes lower than the predetermined reference voltage Vin0, When the output voltage Vout becomes equal to or lower than the reference voltage Vout0, the on / off control of the switching element 9 by the control circuit 10 is performed.

The power Win2 consumed while the switching element 9 is turned on is the input voltage Vin output from the input-side smoothing circuit 5 and the IDRAIN flowing through the high-potential terminal and the low-potential terminal of the switching element 9. In a standby state in which the load 45 does not require power, since the input side voltage Vin is reduced,
Power Win2 consumed by turning on switching element 9 is reduced.

Further, the drain current IDRAIN itself flowing from the high potential side to the low potential side of the switching element 9 while the switching element 9 is on is also the input side voltage Vin.
Is reduced, and the power consumption Win2 of the switching element 9 is also reduced. Therefore, when the load 45 is in the standby state, the power consumption of the input-side power supply circuit is reliably reduced.

In the switching power supply 70 of this embodiment, the switching element 9 and the control circuit 10 are configured as a semiconductor device 23 integrated on the same semiconductor substrate. Therefore, in the semiconductor device 23, the DRAIN terminal to which the high potential side terminal of the switching element 9 is connected and the G terminal to which the low potential side terminal of the switching element 9 is connected.
An ND / SOURCE terminal, a BP terminal to which the control circuit power supply capacitor 11 is connected, an FB terminal to which the photodiode 14b of the photocoupler is connected, and a VIN terminal to which the input voltage detection circuit 7 is connected. At least five terminals are provided as external terminals.

By using such a semiconductor device 23, the number of components of the switching power supply 70 can be significantly reduced, the size can be reduced, and the manufacturing cost can be significantly reduced.

The switching element 9 is connected to the control circuit 1
The on / off control state and the stop state are set based on the current IFB flowing from the FB terminal of 0, and as shown in FIG. 2 (i), an upper limit value IFB2 when shifting from the on / off control state to the stop state, and switching The current IFB may have a hysteresis characteristic by differently setting the lower limit value IFB1 when shifting the on / off control state of the element 9 from the stop state to the on / off control state. With such a configuration, the current I flowing from the FB terminal
When FB rises to the upper limit IFB2, the on / off control of the switching element 9 is stopped, and thereafter, until the current IFB falls to the lower limit IFB1, the on / off control is performed, and by reaching the lower limit IFB1, The on / off control of the switching element 9 is restarted. Thus, the on / off control of the switching element 9 can be stably performed according to the state of the load 45.

In order to provide the upper limit value IFB2 and the lower limit value IFB1 of the current IFB with a hysteresis characteristic, a circuit for detecting the FB terminal current is provided in the control circuit 10, and this circuit is provided with a hysteresis characteristic. Alternatively, the output voltage detection circuit 1 for turning on the light emitting element 14a
4 may be configured to have a hysteresis characteristic.

Although the time chart shown in FIG. 2 is in the non-continuous mode, the VDR
The waveforms of AIN and IDRAIN are only slightly different. Regarding the power consumption effect in the input side power supply circuit,
The same is true.

<Embodiment 2> FIG. 3 is a circuit diagram showing a specific configuration of the switching power supply device shown in FIG. The basic operation of the switching power supply 70 is the same as that of the switching power supply 70 shown in FIG.

The switching element 9 connected to the GATE terminal of the control circuit 10 is constituted by an N-channel MOS transistor, and is turned on when the output of the GATE terminal goes to a high level.

A regulator 29 m is connected to the DRAIN terminal of the control circuit 10.
The voltage of the terminal is adjusted to be constant by the regulator 29m, and the current limiting transistor 29
The signal is supplied to the FB terminal via a. Further, the output of the regulator 29m is the first output having the hysteresis characteristic.
Of the comparator 29n. First
The output of the comparator 29n is supplied to a GATE terminal for controlling the switching element 9 via the first AND circuit 28. The switching element 9 is turned on when the output of the first AND circuit 28 is at a high level.

The control circuit 10 supplies the clock pulse 25c
And a clock circuit 25 that outputs a maximum duty pulse 25d that defines the maximum duty of the on / off control in the switching element 9.

The clock pulse 25c output from the clock circuit 25 is applied to the second AND circuit 29b, and the output of the second AND circuit 29b is applied to the set terminal S of the first RS flip-flop circuit 29d. Has been given. The voltage of the FB terminal is also supplied to the second AND circuit 29b. Therefore, when the photodiode 14b is in the off state, a high-level signal is supplied to the second AND circuit 29b. Second AND circuit 29
b outputs a signal synchronized with the clock pulse 25c while the high-level signal is being supplied from the FB terminal to the first R
The signal is output to the set terminal of the S flip-flop circuit 29d. The output of the first RS flip-flop circuit 29d is
The signal is provided to a first AND circuit 28.

The maximum duty pulse 25d output from the clock circuit 25 is inverted and input to the OR circuit 29c, and the output of the OR circuit 29c is applied to the reset terminal R of the first RS flip-flop circuit 29d. ing. Therefore, the first RS flip-flop circuit 29d
Indicates that the FB terminal is at a high level and the AND circuit 29b
A high-level signal is output to the first AND circuit 28 according to a signal synchronized with the clock pulse 25c output from the, and a low-level signal is output according to an inverted signal of the maximum duty pulse 25d. As a result, the first RS
The output of the flip-flop circuit 29d is defined as a pulse signal having a pulse width smaller than the maximum duty pulse 25d.

The output of the comparator 30a constituting the overcurrent detection circuit 30 is given to the OR circuit 29c connected to the reset terminal of the first RS flip-flop circuit 29d. The comparator 30a of the overcurrent detection circuit 30
FIG. 2 shows that the drain current IDRAIN flowing through the switching element 9 while the switching element 9 is on is
As shown in (g), when a predetermined upper limit value ILIMIT is reached, a high-level signal is output to the OR circuit 29c, and the first RS flip-flop circuit 29d
To the first AND circuit 28 are also made low by the high level output of the comparator 30a, whereby the output of the first AND circuit 28 becomes low and the switching element 9 is turned on. Operation is stopped.

The input-side smoothing circuit 5 includes a first capacitor C1 to which a voltage output from the input-side rectifier circuit 4 is supplied.
And the first capacitor C1 is composed of a second capacitor C2 connected in series, and the second capacitor C2 is connected to the GND / SOURCE of the control circuit 10.
Connected to E terminal. Further, a smoothing capacitance changeover switch 6 is connected in parallel to the second capacitor C2. Normally, the smoothing capacitance changeover switch 6 is in the ON state, and therefore, the first capacitor C1 is in the ground state. Thus, the smoothing capacity changeover switch 6
Is turned on, the DC voltage applied to the input-side smoothing circuit 5 is smoothed only by the smoothing capacitance of the first capacitor C1.

The smoothing capacity changeover switch 6 is arranged as shown in FIG.
As shown in FIG. 7, the load 45 is turned off by a low-level signal from the output-side load state detection circuit 15 indicating that the load 45 is in the standby state. The first and second capacitors C1 and C2 are connected in series with each other, and the smoothing capacity of the input-side smoothing circuit 5 decreases. As a result, the input-side voltage Vin output from the input-side smoothing circuit 5
Is reduced.

The input voltage detecting circuit 7 connected in parallel to the input side smoothing circuit 5 includes two resistors R1 and R2 connected in series and a second comparator 7a connected to the VIN terminal of the control circuit 10. And the potential at the connection point of the resistors R1 and R2 is set via the VIN terminal of the control circuit 10.
The signal is supplied to the + input terminal of the second comparator 7a. Second
The-input terminal of the comparator 7a has a predetermined reference voltage Vin.
0 is input, the second comparator 7a compares the input side voltage Vin with its reference input voltage Vin0, and when the input side voltage Vin becomes equal to or higher than the reference voltage Vin0, the second comparator 7a outputs the high level signal to the second To the set terminal of the RS flip-flop circuit 29f.

The reset terminal of the second RS flip-flop circuit 29f is supplied with the voltage of the FB terminal to which the photodiode 14b is connected, and when the photodiode 14b connected to the FB terminal is off. The high level signal is supplied to the reset terminal of the second RS flip-flop circuit 29f. The inverted output of the second RS flip-flop circuit 29f is provided to the first AND circuit 28 to which the switching element 9 is connected.

When the load 45 is in the standby state and the photodiode 14b is on, the reset terminal of the second RS flip-flop circuit 29f is at low level. In such a state, when the input side voltage Vin of the second comparator 7a provided in the input voltage detection circuit 7 is higher than the reference voltage Vin0, a high level signal is supplied to the set terminal of the second RS flip-flop circuit 29f. Is input to the second RS flip-flop circuit 29f
Becomes the low level, and the output of the first AND circuit 28 to which the switching element 9 is connected becomes the low level. As a result, the switching element 9 is turned off.

On the other hand, when the input side voltage Vin of the second comparator 7a provided in the input voltage detection circuit 7 is lower than the reference voltage Vin0, the low level is applied to the set terminal of the second RS flip-flop circuit 29f. Since the level signal is input, the inverted output of the second RS flip-flop circuit 29f becomes high level, and the output of the first AND circuit 28 to which the switching element 9 is connected becomes high level.
As a result, the switching element 9 enters a state in which on / off control can be performed.

As described above, when the load 45 is in the standby state, similarly to the switching power supply device 70 shown in FIG. 1, the input side voltage Vin output from the input side smoothing circuit 5 in a reduced state. Is a predetermined reference voltage Vin
Only in a state where the voltage is lower than 0, the control circuit 10 is in a state where on / off control of the switching element 9 can be performed. In such a state, when on / off control of the switching element 9 based on the output voltage Vout is performed,
Since the input side voltage Vin is reduced, the power W consumed when the switching element 9 is turned on.
in2 is reduced, and the drain current IDRAIN flowing from the high potential side to the low potential side of the switching element 9 is reduced.
Thus, the power consumption Win2 of the switching element 9 is reduced.

The comparator 7a of the input voltage detecting circuit 7
Is not limited to the configuration provided inside the control circuit 10, but may be provided outside the control circuit 10.

The control circuit 10 is provided with an overheat protection circuit 31a. When the control circuit 10 is overheated to a predetermined temperature or higher, the overheat protection circuit 31a outputs a low-level signal to the first AND circuit 28 to which the switching element 9 is connected, and turns off the switching element 9. State. Therefore, when the control circuit 10 is overheated, the switching element 9 is turned on, so that the control circuit 10 is reliably prevented from being overheated.

The restart trigger circuit 31c provided in the control circuit 10 is provided to release the latch when the output of the overheat protection circuit 31a is latched at a low level.

<Embodiment 3> FIG. 4 is a circuit diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. The switching power supply 70 shown in FIG. 4 also shows a specific configuration of the switching power supply shown in FIG. 1, and the basic operation is the same as that of the switching power supply 70 shown in FIG.

A switching power supply 70 shown in FIG.
The smoothing capacitance changeover switch 6 provided in the input side smoothing circuit 5 of the input side power supply circuit 50 is a power MOSFET.
It is the same as the switch power supply device 70 shown in FIG.

<Embodiment 4> FIG. 5 is a circuit diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. The switching power supply 70 shown in FIG. 5 also shows a specific configuration of the switching power supply 70 shown in FIG. 1, and the basic operation is the same as that of the switching power supply 70 shown in FIG. In a switching power supply device 70 shown in FIG. 5, an input-side smoothing circuit 5 in an input-side power supply circuit 50 is connected in parallel with a rectifier circuit 4 in place of the pair of capacitors C1 and C2 connected in series in FIG. One capacitor C1 and a series circuit of a smoothing capacitance changeover switch 6 and a second capacitor C2 connected in parallel to the first capacitor C1. Other configurations are the same as those of the switching power supply circuit 70 shown in FIG.

As described above, by connecting the series circuit of the second capacitor C2 and the smoothing capacitance changeover switch 6 in parallel with the first capacitor C1, the input of the input signal is switched by the switching of the smoothing capacitance changeover switch 6. The smoothing capacity of the side smoothing circuit 5 can be changed.

<Embodiment 5> FIG. 6 is a circuit diagram showing a configuration of a switching power supply unit according to still another embodiment of the present invention. In the switching power supply 70 shown in FIG.
The primary winding 1a of the transformer 1 is provided with an inductance changeover switch 18 for switching the magnitude of the inductance of the primary winding 1a. The inductance changeover switch 18 is connected so as to short-circuit a connection point between the primary winding 1a and the switching element 9 and an intermediate portion of the primary winding 1a.

When the inductance changeover switch 18 is switched, the inductance of the primary winding 1a in the transformer 1 is changed, and the number of turns of the primary winding 1a to which the input voltage Vin is applied and the number of turns of the secondary winding 1b are changed. Is also changed.

The inductance changeover switch 18 can be switched based on the inverted output of the output side load state detection circuit 15. Output side load state detection circuit 15
Is also supplied to the smoothing capacitance changeover switch 6 provided in the input-side smoothing circuit 5 in the same manner as the switching power supply device 70 in each of the above-described embodiments, and the output-side load state detection circuit 15 When the standby state of 45 is detected, the smoothing capacity switch 6 is switched, and the inductance switch 18 is also switched.

The other structure is the same as that of the switching power supply 70 shown in FIG.

The switching power supply 7 having such a configuration
The operation of 0 will be described based on the time chart shown in FIG.

As shown in FIG. 7D, when the output side load state detection circuit 15 detects that the load 45 is in the standby state, the output of the output side load state detection circuit 15 becomes low level, and The capacitance changeover switch 6 is turned off, and the inductance changeover switch 18 to which the inverted output is given is turned on. When the smoothing capacity switch 6 is turned off, the smoothing capacity of the input-side smoothing circuit 5 is reduced, and the input-side voltage Vin output from the input-side smoothing circuit 5 is reduced.

At this time, since the inductance changeover switch 18 is also switched at the same time, the inductance of the primary winding 1a of the transformer 1 decreases, and the number of turns of the primary winding 1a to which the input voltage Vin is applied is reduced by two. The ratio with the number of turns of the next winding 1b increases. As a result, FIG.
As shown in (g), when the load 45 is in the standby state,
Despite the fact that the input side voltage Vin is reduced, the drain current IDRAIN flowing through the switching element 9 is reduced.
However, this increases more than when the inductance changeover switch 18 is off. However, the drain current ID
RAIN is equal to or less than a predetermined upper limit value ILIMIT (IDRA
IN ≦ ILIMIT).

As described above, when the load 45 is in the standby state, power is reliably supplied to the output side voltage circuit 60 even though the input side voltage Vin of the input side voltage circuit 50 is reduced. be able to.

It is to be noted that such an inductance changeover switch 18 can be provided in any of the switching power supply devices 70 shown in FIGS.

<Embodiment 6> FIG. 8 is a block diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. The switching power supply device 70 is of a positive-polarity step-down chopper type. In the input side power supply circuit 50, an AC voltage output from an AC power supply 2 such as a commercial power supply is grounded via a filter 3. The input side rectifier circuit 4 and the input side smoothing circuit 5 in the state are provided. Then, the output of the input side smoothing circuit 5 is directly applied to the high potential side terminal of the switching element 9. The input-side smoothing circuit 5 is provided with a smoothing-capacity switch 6 that is turned on and off by an output-side load state detection circuit 15. The smoothing capacity of the input-side smoothing circuit 5 is switched by the smoothing-capacity switch 6. Can be

The output side power supply circuit 60 provided at the low potential side terminal of the switching element 9 is provided with an output DC converting means 55. The output DC converting means 55 includes: a regenerative diode 20 having a cathode connected to the low potential side terminal of the switching element 9 and an anode grounded; the coil 21 having one end connected to the low potential side terminal of the switching element 9;
It has a capacitor 22 provided between the other end of the coil 21 and the ground.

An output main terminal 17a is connected to a connection point between the coil 21 and the capacitor 22, and a load 45 is connected between the output main terminal 17a and the ground.
The voltage output from the switching element 9 is converted by the output DC converting means 55 into a positive DC voltage having an absolute value lower than the absolute value of the DC input voltage output from the input-side smoothing circuit 5, and the output main terminal. 17a to the load 45.

The output-side main terminal 17a is connected to the output voltage detection circuit 14 and the output-side load state detection circuit 15, each of which is grounded, in parallel with the load 45, respectively. The output voltage detection circuit 14 includes an output-side main terminal 17a.
Based on the output voltage Vout output from the
Is turned on, the light emitting element 14a of the photocoupler is turned on. The photodiode 14b of the photocoupler irradiated with light from the light emitting element 14a is connected to the FB terminal of the control circuit 10.

The output side load state detection circuit 15 is
Is detected, and when the load 45 is in the standby state,
The smoothing capacitance changeover switch 6 of the input side smoothing circuit 5 is turned off.

The other configuration is the same as the configuration of the switching power supply device shown in FIG.

In the switching power supply 70 of the positive step-down type chopper type shown in FIG. 8, the input side power supply circuit 50 and the output side power supply circuit 60 are insulated.
When the output of the output voltage detection circuit 14 is insulated and the control circuit 10
FB terminal. For this reason, the output voltage detected by the output voltage detection circuit 14 is detected regardless of the ON state and the OFF state of the switching element 9.

The switching power supply 7 having such a configuration
The operation of 0 will be described based on the time chart shown in FIG. In the control circuit 10, the control circuit power supply capacitor 11 is charged by the current supplied from the DRAIN terminal. When the power supply voltage VBP of the control circuit power supply capacitor 11 reaches a predetermined reference voltage VBP0, the control circuit 10 starts. As a result, the control circuit 10 starts the on / off control of the switching element 9.

When the on / off control of the switching element 9 by the control circuit 10 is started, the input side voltage Vin of the high potential side terminal of the switching element 9 is changed to the switching element 9.
Is turned on, the coil 21 passes through the low potential side terminal.
Supplied to While the switching element 9 is off, no current is supplied to the coil 21, so that the electric energy stored in the coil 21 is output to the output-side main terminal 17 a via the regenerative diode 20. Is done. Then, from the output side main terminal 17a, a positive output voltage Vout is output to the load 45.

The regenerative diode 20 for rectifying the voltage output from the switching element 9 needs to have the same withstand voltage as the switching element 9 because electric energy is intermittently supplied from the coil 21. As for the recovery characteristics, the higher the speed, the better the voltage conversion efficiency. Therefore, Trr (reverse recovery time, reverse current time) may be about 50 ns.

The switching power supply 7 having such a configuration
0 is also similar to the switching power supply 70 shown in FIG.
When the output voltage detection circuit 14 detects that the output voltage Vout has risen above the reference voltage Vout0 and the load 45 is in a load fluctuating state, the light emitting element 14a of the photocoupler is turned on and the photodiode is turned on. 14b
Is turned on, the operation of the control circuit 10 is stopped,
The on / off control of the switching element 9 stops. When the switching element 9 is turned off, the voltage output to the output DC converter 55 decreases, and the output voltage Vout also gradually decreases. Then, the output voltage Vout is changed to the reference voltage Vout0.
When the output voltage becomes equal to or less than that, the light emitting element 14a of the photocoupler is turned off by the output voltage detection circuit 14, and the photodiode 14b is also turned off. Thereby, the control circuit 10 is restarted, and the on / off control of the switching element 9 is restarted.

By repeating such operations, the output voltage Vout is controlled to be constant at the reference voltage Vout0. In addition, as the load 45 approaches the standby state, the output voltage Vout changes to the reference voltage Vout.
The time until it becomes 0 or less becomes longer, the stop time of the control circuit 10 becomes longer, and the time during which the on / off control of the switching element 9 is stopped becomes longer.

Further, when the output side load state detecting circuit 15 detects that the load 45 is in the standby state, the smoothing capacity changeover switch 6 is switched, and the smoothing capacity of the input side smoothing circuit 5 is changed. Is switched. Thereby, the smoothing capacity of the input side smoothing circuit 5 is reduced, and the input side voltage Vin output from the input side smoothing circuit 5 is reduced. As a result, when the load 45 is in the standby state, the drain current IDR
AIN is reduced, and the power consumed by switching element 9 is reduced.

Switching power supply circuit 70 of the present embodiment
Then, for example, the input-side smoothing circuit 5 of the input-side power supply circuit 50
100V or more DC input side voltage Vin output from
However, from the output side main terminal 17a of the output side power supply circuit 60,
It is output as a DC output voltage Vout of 25 V or less. Therefore, it is suitably used as a switching power supply device for home electric appliances and the like.

<Embodiment 7> FIG. 10 is a block diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. Switching power supply 7 shown in FIG.
0 denotes a negative step-down chopper system, and the output DC conversion means 55 of the output side power supply circuit 60 connected to the low potential side terminal of the switching element 9 shows the polarity of the output voltage Vout in FIG. Output voltage Vo of switching power supply
It is configured to have a negative polarity opposite to the polarity of ut.

In the output DC converter 55 of the switching power supply 70 shown in FIG. 10, one end of the coil 21 is connected to the low potential side terminal of the switching element 9.
The cathode of the regenerative diode 20 is connected. The other end of the coil 21 is grounded, and the anode of the regenerative diode 20 is grounded via a capacitor 22. The other configuration is the same as the configuration of the switching power supply 70 shown in FIG.

In the switching power supply 70 of the negative polarity step-down type chopper type shown in FIG. 10, the input side power supply circuit 50 is provided similarly to the switching power supply 70 shown in FIG.
And the output side power supply circuit 60 are insulated, and the output of the output voltage detection circuit 14 is in an insulated state.
It is given to the B terminal. For this reason, the output voltage detected by the output voltage detection circuit 14 is detected regardless of the ON state and the OFF state of the switching element 9.

The switching power supply 7 having such a configuration
0, the output voltage Vo applied to the output side main terminal 17a
Except that ut has a negative polarity, it operates in the same manner as the switching power supply device 70 shown in FIG. 8, and therefore, when the load 45 is in the standby state, the power consumption when the switching element 9 is turned on is reduced.

<Eighth Preferred Embodiment> FIG. 11 is a circuit diagram showing a configuration of a switching power supply device according to still another embodiment of the present invention. A switching power supply 70 shown in FIG. 11 is an improvement of the conventional switching power supply shown in FIG.
An output side load state detection circuit 15 for detecting the state of the load 45 connected to the output side main terminal 17a is connected to the ROL terminal in parallel with the control circuit power supply capacitor 11. Then, based on the output of the output-side load state detection circuit 15, the smoothing capacity changeover switch 6 provided in the input-side smoothing circuit 5 for switching the size of the smoothing capacity is switched.

The control circuit power supply capacitor 11 connected to the CONTROL terminal of the control circuit 10 is connected to the control circuit 10 via the control circuit 10 through the DRAIN terminal until the capacitor is started.
When the current is supplied to the NTRO terminal, the voltage at both ends increases. When the voltage at both ends becomes equal to or higher than a voltage set in advance in the control circuit 10, the control circuit 10 starts the on / off control of the switching element 9. At the same time D
CONTR from the RAIN terminal via the control circuit 10
No current is supplied to the OL terminal.

When the control circuit 10 is started, the pulsating current flows through the primary winding 1a of the transformer 1 by the on / off control of the switching element 9, and therefore the pulsating current also flows through the secondary winding 1b of the transformer 1. Flows. As a result, the output voltage Vout applied to the load 45 connected to the output-side main terminal 17a via the output DC converter 55 increases.

The output voltage Vout is applied to the output voltage detection circuit 1
4, the light emitting element 14a is turned on, and the photodiode 1
The feedback signal is transmitted to 4b, and the photodiode 14b turns on. When the photodiode 14b is turned on, a current proportional to the pulsating current flowing through the secondary winding 1b flows through the auxiliary winding 1c while the switching element 9 is turned off. 11 is supplied. As a result, the control circuit 10 continuously performs the on / off control of the switching element 9.

CONTROL terminal voltage (power supply voltage across control circuit power supply capacitor 11) V of control circuit 10
c is determined by the light emitting element 14a which is turned on by the output voltage detection circuit 14 while the control circuit 10 is operating.
When the photodiode 14b is turned on, a current is supplied from the auxiliary winding 1c, and the voltage is always controlled to a preset voltage.

However, since the period during which Vout ≧ Vout0 changes depending on the load state of the load 45, when the load 45 approaches the standby state, the current supply from the auxiliary winding 1c increases and the power supply of the CONTROL terminal is The voltage Vc increases, and conversely, when the load 45 enters a heavy load state, the amount of current supplied from the auxiliary winding 1c decreases, so that the power supply voltage Vc at the CONTROL terminal decreases.

The output side load state detection circuit 15 detects the state of the load 45 based on the power supply voltage Vc of the control circuit power supply capacitor 11, and the control is performed when the load 45 enters the standby state. When the power supply voltage Vc of the circuit power supply capacitor 11 reaches a predetermined upper limit maximum value VC3 (see FIG. 12), the input-side smoothing circuit 5
Is switched over. Thereby, the smoothing capacity of the input side smoothing circuit 5 is reduced. Other configurations are the same as those of the conventional switching power supply device shown in FIG.

FIG. 12 is a time chart showing the operation of the switching power supply device shown in FIG. FIG. 12 (a)
Indicates the input side voltage Vin, and FIG.
The current IDRAIN flowing through the switching element 12 is shown. FIG. 12C schematically shows the state of the load 45. FIGS. 12D to 12I are respectively
FIG. 12A is an enlarged view of the time axis, and FIG. 12D shows an output signal of the output-side load state detection circuit 15. FIG. 12E shows the switching element 9.
Of the high potential side terminal VDRAIN. Figure 1
2 (f) indicates the voltage Vc of the CONTROL terminal of the control circuit 10. FIG. 12G shows the current IDRAIN of the switching element 9. FIG. 12 (h)
The output voltage Vout is shown.

Based on the time chart shown in FIG.
The operation of the switching power supply device 70 shown in FIG. 11 will be described.

The control circuit 10 includes the primary winding 1 of the transformer 1
The current supplied from a to the DRAIN terminal of the control circuit 16 is supplied to the CONTROL terminal via the control circuit 10 and the voltage across the control circuit power supply capacitor 11 increases. When the voltage becomes higher than the set voltage, it starts.

When the control circuit 10 is started up and enters a steady operation state, the output voltage Vout becomes higher than the reference voltage Vout0 and the photodiode 14b is turned on, the auxiliary winding 1c is turned off while the switching element 9 is turned off. Is supplied to the control circuit power supply capacitor 11.

When the control circuit 10 enters the steady state, CON
The power supply voltage Vc of the TROL terminal is controlled to be a lower limit value Vc1 set in the control circuit 10 in advance. Although the power supply voltage Vc has a ripple, to be precise, the time chart shown in FIG. 12 shows an average voltage in consideration of the ripple. When the load 45 is in a heavy load state, the power supply voltage Vc becomes lower than a preset lower limit value Vc1 (Vc <Vc1) because the amount of current supplied from the auxiliary winding 1c decreases. Thus, the on-duty DC of the switching element 9 becomes the maximum on-duty DCmax, and the time during which the switching element 9 is turned on is lengthened.

When the load 45 approaches the standby state from the heavy load state, the amount of current supplied from the auxiliary winding 1c gradually increases, and the power supply voltage Vc of the CONTROL terminal of the control circuit 10 is increased.
Is between the lower limit value Vc1 and a preset intermediate value Vc2 (Vc1 ≦ Vc ≦ Vc2). Thereby, the on-duty DC of the switching element 9 is controlled between the maximum duty DCmax and the minimum duty DCmin.

When the load 45 further approaches the standby state,
When the power supply voltage Vc of the CONTROL terminal of the control circuit 10 is
The intermediate value Vc2 or more and a preset upper limit value Vc
3 or less (Vc2 ≦ Vc ≦ Vc3). This allows
The on-duty DC of the switching element 9 is controlled to the minimum duty DCmin.

As described above, since the on-duty by the switching element 9 is reduced, the output-side power supply circuit 6
The amount of power supplied to 0 decreases, and the output voltage Vout decreases.

When the load 45 enters the standby state, the CONTROL terminal voltage Vc of the control circuit 10 becomes higher than the preset upper limit value Vc3 (Vc3 <Vc), and the output load state detection circuit 15 operates. As a result, the smoothing capacity changeover switch 6 operates, and the smoothing capacity of the input-side smoothing circuit 5 is reduced. The ON / OFF control of the switching element 9 by the control circuit 10 is performed only during the period when the input voltage Vin is lower than the reference voltage Vin0 (Vin <Vin0) due to the output current from the input voltage detection circuit 7.

When the load 45 is in the standby state, the output voltage V
When the output falls below the reference voltage Vout0 and the on / off control of the switching element 9 is performed, the switching voltage of the switching element 9 is proportional to the input voltage Vin because the input voltage Vin is reduced. Of the input side power supply circuit is reduced. Moreover, since the drain current IDRAIN of the switching element 9 itself is reduced, the power consumed when the switching element 9 is turned on is also reduced, and the power consumption of the input-side power supply circuit 50 is further reduced.

In the switching power supply 70 of this embodiment, the switching element 9, the control circuit 10, and the output side load state detection circuit 15 are configured as a semiconductor device 23 integrated on the same semiconductor substrate. I have. Therefore, the semiconductor device 23 includes a terminal to which the high potential side terminal of the switching element 9 is connected, a terminal to which the low potential side terminal of the switching element 9 is connected, and a terminal to which the control circuit power supply capacitor 11 is connected. At least five terminals including a terminal to which the input voltage detection circuit 7 is connected and a terminal to which the output-side load state detection circuit 15 is connected are provided as external terminals.

Therefore, by configuring the switching power supply device 70 using such a semiconductor device 23, the number of components of the switching power supply device 70 can be significantly reduced, and the switching power supply device 70 can be downsized. Moreover, it can be manufactured at low cost.

The control circuit 10 of the switching power supply 70 of this embodiment is provided with an overheat protection means so that when the control circuit 10 is overheated, the switching element 9 is turned on.
May be stopped. Although the output-side load state detection circuit 15 is provided inside the semiconductor device 23 and outside the control circuit 10, it may be provided inside the control circuit 10.

<Embodiment 9> FIG. 13 is a circuit diagram showing the configuration of still another example of the embodiment of the switching power supply device of the present invention. Switching power supply 7 shown in FIG.
0 specifically shows the configuration of the switching power supply 70 shown in FIG. 11, and the basic configuration and operation are the same as those of the switching power supply 70 shown in FIG.

N-channel MOS transistor switching element 9 connected to GATE terminal of control circuit 10
Is given by the high level output of the first AND circuit 28.
Turned on.

The DRAIN terminal of the control circuit 10 is connected to a control circuit power supply capacitor 11 via a power supply terminal changeover switch provided in the control circuit 10.
It is connected to the TROL terminal. CON of control circuit 10
The power supply voltage Vc of the TROL terminal is provided to the + terminal of the first comparator 29x having a hysteresis characteristic. The first comparator 29x is provided for determining a voltage for starting and stopping the control circuit 10. For example, when the power supply voltage Vc becomes higher than 5.7V, the first comparator 29x outputs a high-level signal and outputs a high-level signal. When the voltage drops below 0.7 V, a low level signal is output. The output of the first comparator 29x is input to the timer intermittent operation circuit 26, and the output of the timer intermittent operation circuit 26 is provided to the first AND circuit 28.

The timer intermittent operation circuit 26 includes the auxiliary winding 1
It operates when the power supply from c to the control circuit power supply capacitor 11 via the photodiode 14b becomes zero for some reason, for example, when the load 45 is short-circuited for some reason.

The reference voltage of the first comparator 29x has a hysteresis characteristic, and this reference voltage is a predetermined starting voltage Vc of the control circuit 10. start and stop voltage Vc It is a stop. The voltage Vc across the control circuit power supply capacitor 11 decreases, and the stop voltage Vc
When the value falls below stop (Vc <Vc stop), the control circuit 10 tries to stop. In this case, the current to the control circuit power supply capacitor 11 is supplied again from the DRAIN terminal through the control circuit 10. The voltage Vc across the terminal 11 gradually increases. Then, the voltage Vc across the control circuit power supply capacitor 11 becomes the starting voltage Vc. When it exceeds start (Vc>
Vc start), from the DRAIM terminal to the control circuit 10
The current supply to the control circuit power supply capacitor 11 via the inside stops.

Vc> Vc It will be a start,
The on / off control of the switching element 9 by the control circuit 10 is in a pause state. Therefore, no current is supplied from the auxiliary winding 1c, and therefore no current is supplied to the control circuit power supply capacitor 11, and the voltage Vc across the control circuit power supply capacitor 11 again decreases, and the control circuit power supply capacitor 11 is the stop voltage Vc sto
p (Vc <Vc stop). The timer intermittent operation circuit 26 performs this operation, that is, the voltage Vc across the control circuit power supply capacitor 11 becomes the stop voltage Vc sto
The number of times less than p is counted, and the control circuit 10 performs the on / off control of the switching element 9 only once for the number of times set in advance by the timer intermittent operation circuit 26. Thus, the timer intermittent operation circuit 2
6 has a protection function of the switching power supply device.

The power supply voltage Vc of the control circuit 10, which is the voltage of the CONTROL terminal, is applied to the resistor 29e and the second comparator 29.
f and a shunt regulator constituted by the switch element 29g. The constant power supply voltage Vc of the control circuit 10 is supplied to the second comparator 29.
f, the power supply voltage Vc is equal to the reference voltage Vc.
When it becomes larger than 1, the switch element 29g is turned on by the output of the second comparator 29f, and the PWM is connected to the resistor 29h from the CONTROL terminal via the switch element 29g.
A control current is supplied.

The output of the second comparator 29f is
The control circuit 1 is also provided to the overvoltage protection circuit 31b.
When the power supply voltage Vc of 0 becomes equal to or higher than a predetermined voltage, the overvoltage protection circuit 31b operates to output a high-level signal to the set terminal of the first RS flip-flop 31d via the OR circuit 31e. As a result, the inverted output of the first RS flip-flop 31d becomes low level, and the low level signal is output to the first AND circuit 28.
When a low-level signal is input, the output of the first AND circuit 28 becomes low, and the switching element 9 is turned off.

The output of the overheat protection circuit 31a is also supplied to the OR circuit 31e. When the control circuit 10 is overheated to a predetermined temperature or higher, the first RS flip-flop is connected via the OR circuit 31e. A high level signal is output to the set terminal of the loop 31d. Thereby, the first RS
The inverted output of the flip-flop 31d goes low, the output of the first AND circuit 28 goes low, and the switching element 9 is turned off.

The first RS flip-flop 31d
The reset terminal of is supplied with the output of the restart trigger circuit 31c. When the control circuit 10 is restarted after the output of the overvoltage protection circuit 31b or the overheat protection circuit 31a becomes high level, Startup trigger circuit 31
c outputs a high-level signal. Thereby, the first
Of the RS flip-flop 31d becomes high level, and the output of the first AND circuit 28 turns on the switching element 9.

The operation of the shunt regulator causes the resistance 2
When the PWM control current is applied to 9h, a voltage proportional to the power supply voltage Vc is generated across the resistor 29h. The voltage generated at both ends of the resistor 29h is supplied to the low-pass filter 3
8 is supplied to the + terminal of the third comparator 29i.

The voltage of the triangular wave pulse 25s output from the clock circuit 25 is input to the minus terminal of the comparator 29i, and the output of the third comparator 29i is
Through the R circuit 29y, the second RS flip-flop 2
9z is provided to the reset terminal.

When the voltage of the low-pass filter 38 becomes lower than the voltage of the triangular wave pulse 25s output from the clock circuit 25, the third comparator 29i outputs a high-level signal and outputs the second RS Flip-flop 29
A high level signal is output to the reset terminal of z. Therefore, the third comparator 29i corresponds to the power supply voltage Vc,
Outputs high-level signals with different time widths.

The set pulse of the second RS flip-flop 29z is supplied with the clock pulse 25c output from the clock circuit 25. The output of the second RS flip-flop 29z is supplied to the first AND circuit 28. Has been given. Therefore, in synchronization with the clock pulse 25c output from the clock circuit 25, the second RS flip-flop 29z outputs a high-level signal, and the high-level signal is a reset signal having a different time width corresponding to the power supply voltage Vc. Reset by Therefore, the first AN
An on-duty pulse signal corresponding to the power supply voltage Vc is applied to the D circuit 28, and the switching element 9 to which the output of the first AND circuit 28 is applied can be turned on in synchronization with the pulse signal.

The first AND circuit 28 is also provided with a maximum duty pulse 25d output from the clock circuit 25. The first AND circuit 28 has a small pulse width equal to or smaller than the maximum duty pulse 25d and has a high pulse width. It outputs a level signal.

The DRAIN terminal of the control circuit 10 is connected to the + input terminal of the comparator 30a constituting the overcurrent detection circuit 30. The comparator 30a of the overcurrent detection circuit 30
The on-resistance of the switching element 9 is used as an overcurrent level detection resistance, and the drain current IDRAIN flowing through the switching element 9 is monitored while the switching element 9 is on. When the drain current IDRAIN reaches a predetermined upper limit value ILIMIT. , A high-level signal to the reset terminal of the second RS flip-flop 29z via the OR circuit 29y. Therefore, the overcurrent detection circuit 30
Becomes high level, the switching element 9 is turned off.

The CONTROL terminal of the control circuit 10
Output-side load state detection circuit 1 provided in control circuit 10
5 is connected. The output of the output side load detection circuit 15 is supplied from the CIN terminal of the control circuit 10 to the input side smoothing circuit 5.
, And to a third OR circuit 39.

The input side smoothing circuit 5 has first and second capacitors C1 and C2 connected in series, and a smoothing capacitance changeover switch 6 is connected in parallel to the second capacitor C2. Have been. Normally, the smoothing capacitance changeover switch 6 is in an ON state, and the capacitance of the first capacitor C1 is the smoothing capacitance of the input-side smoothing circuit 5, but the load 45 is in the standby state and the control signal is CONTROL.
When the output side load state detection circuit 15 detects that the power supply voltage Vc at the L terminal has risen above a predetermined upper limit maximum value Vc3, the output of the output side load state detection circuit 15 becomes low level and the smoothing capacity switching is performed. When the switch 6 is turned off, the smoothing capacity of the input-side smoothing circuit 5 is reduced to a capacity in which the first and second capacitors C1 and C2 are connected in series.

The output of the comparator 7a provided in the input voltage detection circuit 7 is also supplied to the third OR circuit 39.
The output of the third OR circuit 39 is input to the first AND circuit 28.

The input voltage detecting circuit 7 includes an input side smoothing circuit 5
Only when the input side voltage Vin reduced by the above becomes lower than the reference voltage Vin0 of the comparator 7a, a high level signal is output to the third OR circuit 39.

When the output side load state detection circuit 15 detects that the power supply voltage Vc of the CONTROL terminal has become higher than the upper limit value Vc3 and outputs a low level signal, the smoothing capacitance of the input side smoothing circuit 5 is output. Is reduced, and one input of the third OR circuit 39 is set to a low level.

As described above, in the state where one input of the OR circuit 39 is at the low level, the input side voltage Vin in the reduced state is input from the input side smoothing circuit 5 having the reduced smoothing capacitance. Input to the voltage detection circuit 7. Then, when the input side voltage Vin thus reduced becomes lower than the predetermined reference voltage Vin0, the output of the comparator 7a of the input voltage detection circuit 7 becomes high level, and the third OR
The other terminal of the circuit 39 goes high. As a result, the output of the third OR circuit 39 becomes high level, a high-level signal is input to the first AND circuit 28, and the on / off control of the switching element 9 based on the detection result of the output voltage detection circuit 14 can be performed. State.

The switching power supply 7 having such a configuration
0, the same operation as the switching device 70 shown in FIG. 11 is realized. When the load 45 is in the standby state, the output voltage Vout is reduced to the reference voltage only when the input voltage Vin is equal to or lower than the reference voltage Vin0. When the state becomes higher than Vout0, the on / off control of the switching of the switching element 9 by the control circuit 10 is performed by the reduced input side voltage Vin. Therefore, since the drain current IDRAIN of the switching element 9 which is proportional to the input voltage Vin is reduced, the power consumption of the input power supply circuit 50 is reduced and the switching element 9 is consumed when the switching element 9 is turned on. The power is also reduced, and the power consumption of the input-side power supply circuit 50 is reliably reduced.

<Embodiment 10> FIG. 14 is a circuit diagram showing a configuration of a switching power supply unit according to still another embodiment of the present invention. Switching power supply 70 shown in FIG.
Is an input-side smoothing circuit 5 provided in the input-side power supply circuit 50.
13 is the same as the switch power supply device 70 shown in FIG. 13 except that the smoothing capacitance changeover switch 6 is constituted by a power MOSFET.

<Embodiment 11> FIG. 15 is a circuit diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. Switching power supply device 70 shown in FIG.
11 also shows a specific configuration of the switching power supply 70 shown in FIG. 11, and the basic operation is the same as that of the switching power supply 70 shown in FIG. The switching power supply device 70 shown in FIG. 15 has a rectifier as the input-side smoothing circuit 5 provided in the input-side power supply circuit 50, instead of the pair of capacitors C1 and C2 connected in series in the switching power supply device 70 shown in FIG. It comprises a first capacitor C1 connected in parallel with the circuit 4, and a series circuit of a smoothing capacitance changeover switch 6 and a second capacitor C2 connected in parallel to the first capacitor C1. . Other configurations are the same as those of the switching power supply circuit 70 shown in FIG.

As described above, by connecting the series circuit of the second capacitor C2 and the smoothing capacitance changeover switch 6 in parallel with the first capacitor C1, the smoothing capacitance of the input side smoothing circuit 5 can be changed. can do.

<Twelfth Embodiment> FIG. 16 is a circuit diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. Switching power supply device 70 shown in FIG.
Is a switching power supply device 70 shown in FIG.
The primary winding 1a provided on the input side of the transformer 1 is provided with an inductance changeover switch 37 for switching the magnitude of the inductance of the primary winding 1a. The inductance changeover switch 37 is connected so as to short-circuit a connection point between the primary winding 1a and the switching element 9 and an intermediate portion of the primary winding 1a.

When the on / off state of the inductance changeover switch 37 is switched, the inductance of the primary winding 1a in the transformer 1 is switched, and the number of turns of the primary winding 1a to which the input voltage Vin is applied and the secondary winding 1b. The ratio with the number of turns is also changed.

The inductance change-over switch 37 can be switched based on the output of the output-side load state detection circuit 15.

The inductance changeover switch 37 is
When the output side load state detection circuit 15 detects that the load 45 is in the standby state, the output from the output side load state detection circuit 15 is inverted and given. Other configurations are the same as those of the switching power supply device 70 shown in FIG.

FIG. 17 is a time chart showing the operation of switching power supply device 70 shown in FIG. 16. Based on this time chart, the operation of switching power supply device 70 shown in FIG. 16 will be described.

As shown in FIG. 17D, when the output side load state detection circuit 15 detects that the load 45 is in the standby state, and the output of the output side load state detection circuit 15 becomes low level, The capacitance switch 6 is turned off, and the inductance switch 37 is turned on. When the smoothing capacity switch 6 is turned off, the smoothing capacity of the input-side smoothing circuit 5 is reduced, and the input-side voltage Vin output from the input-side smoothing circuit 5 is reduced.

At this time, since the inductance changeover switch 37 is turned on at the same time, the inductance of the primary winding 1a of the transformer 1 is reduced, and the number of turns of the primary winding 1a to which the input voltage Vin is applied is reduced by two. The ratio with the number of turns of the next winding 1b increases. As a result, FIG.
As shown in (g), when the load 45 is in the standby state,
Despite the fact that the input side voltage Vin is reduced, the drain current IDRAIN flowing through the switching element 9 is reduced.
However, this increases more than when the inductance changeover switch 37 is off. However, the drain current ID
RAIN is equal to or less than a predetermined upper limit value ILIMIT (IDRA
IN ≦ ILIMIT).

As described above, since the load 45 enters the standby state, the supply of the output power Vout to the load 45 does not become insufficient even if the input voltage Vin is reduced. Even if the power consumption at 50 is reduced, there is no possibility that the output side voltage Vout is affected.

It should be noted that such an inductance changeover switch 37 can be provided in any of the switching power supply devices 70 shown in FIGS.

<Thirteenth Preferred Embodiment> FIG. 18 is a circuit diagram showing a configuration of a switching power supply according to still another preferred embodiment of the present invention. Switching power supply 70 shown in FIG.
Is a positive-polarity step-down chopper type, in which an AC voltage output from an AC power supply 2 such as a commercial power supply is supplied to the input side of the input side power supply circuit 50 through the filter 3, where each of the input side is grounded. It is provided to the rectifier circuit 4 and the input side smoothing circuit 5. Then, the output of the input side smoothing circuit 5 is directly applied to the high potential side terminal of the switching element 9. The input-side smoothing circuit 5 includes an output-side load state detection circuit 1
A smoothing capacity changeover switch 6 that is on / off controlled by 5 is provided, and the smoothing capacity of the input side smoothing circuit 5 is switched by the smoothing capacity changeover switch 6.

The low potential side terminal of the switching element 9
The output side power supply circuit 60 having the output DC conversion means 55 is connected. The output DC converting means 55 has a regenerative diode 20 having a cathode connected to the low potential side terminal of the switching element 9, and a coil 21 having one end connected to the low potential side terminal of the switching element 9. ing. The anode of the regenerative diode 20 is grounded. The other end of the coil 21 is grounded via the capacitor 22 and is connected to the output side main terminal 17a. A load 45 is connected between the output side main terminal 17a and the ground.

The voltage output from the switching element 9 is converted by the output DC converting means 55 into a positive DC voltage having an absolute value lower than the absolute value of the DC input voltage output from the input-side smoothing circuit 5 and output. Load 4 from the side main terminal 17a
5 is output.

The output voltage detecting circuit 14 is connected to the output side main terminal 17a. The output voltage detection circuit 14 detects the output voltage Vout output from the output side main terminal 17a, and outputs the detection result to the CONTROL of the control circuit 10.
Output to L terminal.

The CONTROL terminal of the control circuit 10
As in the switching power supply device 70 shown in FIG. 11, the output-side load state detection circuit 15 is connected, and the output-side load state detection circuit 15 is connected to a control circuit power supply that is charged by a current output from the switching element 9. Based on the power supply voltage Vc of the capacitor 11, it detects that the load 45 is in the standby state, and switches the smoothing capacitance switch 6 of the input-side smoothing circuit 5.

The other configuration is the same as that of the switching power supply 70 shown in FIG. 11, and the switching element 9 is on / off controlled by the control circuit 10.

The switching power supply 7 having such a configuration
The operation of 0 will be described with reference to the time chart shown in FIG. By the current supplied from the DRAIN terminal,
When the voltage of the control circuit power supply capacitor 11 rises and reaches a predetermined reference voltage, the control circuit 10 starts up and starts the on / off control of the switching element 9.

When the on / off control of the switching element 9 by the control circuit 10 is started, the input voltage Vin of the high potential side terminal of the switching element 9 is changed to the switching element 9.
Is turned on, the coil 21 passes through the low potential side terminal.
When the switching element 9 is turned off, the electric energy stored in the coil 21 is output to the output-side main terminal 17a via the regenerative diode 20. From the output side main terminal 17a, a positive output voltage Vout is output to the load 45.

The regeneration diode 20 for rectifying the voltage output from the switching element 9 is similar to the regeneration diode of the switching power supply 70 shown in FIG.
The same breakdown voltage as that of the switching element 9 is required, and Trr (reverse recovery time, reverse current time) is 50 n
It may be about s.

In the switching power supply 70 of the positive polarity step-down type chopper type shown in FIG.
When the switching element 9 is turned on, the reference potential Vc1 of the NTRO terminal voltage Vc is higher by the input side voltage Vin and becomes higher. However, when the switching element 9 is turned off, the input side voltage Vin is not added. For this,
The output voltage detection circuit 14 detects the output voltage Vout only when the switching element 9 is in the off state. Then, the output voltage detection circuit 1
On / off control of the switching element 9 is performed based on the output voltage Vout detected at 4.

The switching power supply 7 having such a configuration
In the case of 0 as well, as in the switching power supply device 70 shown in FIG. The output voltage Vout from the output side main terminal 17a is equal to the reference voltage Vo.
A current higher than ut0 and flowing through the auxiliary winding 1c is supplied to the control circuit power supply capacitor 11. Then, the power supply voltage Vc which is a voltage between both ends of the CONTROL terminal.
Becomes lower than a preset lower limit value Vc1 (Vc
<Vc1) and the on-duty D of the switching element 9
C is the maximum on-duty DCmax, and is between the lower limit value Vc1 and a preset intermediate value Vc2 (V
When c1 ≦ Vc ≦ Vc2), the on-duty DC of the switching element 9 is controlled between the maximum duty DCmax and the minimum duty DCmin, and the CONTROL terminal voltage Vc of the control circuit 10 is set to the intermediate value Vc.
When it is not less than c2 and not more than a preset upper limit value Vc3 (Vc2 ≦ Vc ≦ Vc3), the on-duty DC of the switching element 9 is controlled to the minimum duty DCmin.

As described above, since the on-duty by the switching element 9 is reduced, the output side power supply circuit 6
The amount of power supplied to 0 decreases, and the output voltage Vout decreases. By repeating such an operation, the output voltage Vout is controlled to be constant at the reference voltage Vout0.

Further, when the output side load state detection circuit 15 detects that the load 45 is in the standby state,
Since the smoothing capacity of the input side smoothing circuit 5 is switched, the smoothing capacity of the input side smoothing circuit 5 is reduced, and the input side voltage Vin output from the input side smoothing circuit 5 is reduced. When the load 45 is in the standby state, the input voltage Vin ≦ Vin0 and the output voltage Vout ≧ Vo
The ON / OFF control of the switching element 9 is performed only during the period of ut0.

In this case, the input side voltage Vin is the reference voltage V
Since it is lower than in0, the switching element 9
, The drain current IDRAIN flowing when the transistor is turned on is reduced, and the power consumed by the switching element 9 is reduced.

The output voltage detecting circuit 14 comprises a series connection circuit of a switching diode and a zener diode, or a voltage drop type element such as a diode or a transistor instead of this zener diode, or a voltage drop type element and a resistor. And a circuit block combining the above.

In the switching power supply according to the present embodiment, control circuit 10 may be provided with overheat protection means.

<Embodiment 14> FIG. 20 is a block diagram showing a configuration of a switching power supply unit according to still another embodiment of the present invention. This switching power supply 70
Negative voltage step-down chopper method, output voltage Vo
out of the switching power supply 70 shown in FIG.
And the connection between the output voltage detecting circuit 14 and the output DC converting means 55 of the output side power supply circuit 60 connected to the low potential side terminal of the switching element 9 so as to have a negative polarity opposite to the polarity of the output voltage. Only the state is different from the switching power supply device 70 shown in FIG.

In the output DC converting means 55 of the switching power supply 70 shown in FIG. 20, one end of the coil 21 is connected to the low potential side terminal of the switching element 9, and a regenerative diode is connected to the low potential side terminal of the switching element 9. Twenty cathodes are connected. The anode of the regenerative diode 20 is grounded via the capacitor 22, and
It is connected to the output side main terminal 17a. Output main terminal 1
A load 45 is connected between 7a and the ground.

[0231] The output voltage detection circuit 14 connected to the CONTROL terminal of the control circuit 10 is grounded.

In the switching power supply 70 of the negative polarity step-down type chopper type shown in FIG. 20, the CONT of the control circuit 10 is connected similarly to the switching power supply 70 shown in FIG.
When the switching element 9 is turned on, the reference potential Vc1 of the ROL terminal voltage Vc is increased by the input voltage Vin, but when the switching element 9 is turned off, the input voltage Vin is not added. For this reason, the output voltage detection circuit 14 detects the output voltage Vout only when the switching element 9 is in the off state. Then, on / off control of the switching element 9 is performed based on the output voltage Vout detected by the output voltage detection circuit 14.

The switching power supply 7 having such a configuration
0, the output voltage Vo applied to the output side main terminal 17a
Except that ut has a negative polarity, it operates in the same manner as the switching power supply device 70 shown in FIG. 18, and when the load 45 is in a standby state, the input side voltage Vin is reduced to be lower than the reference voltage Vin0. The power consumption of the switching element 9 is reduced because the ON / OFF control of the switching element 9 is performed only when the power consumption has decreased.

<Embodiment 15> FIG. 21 is a circuit diagram showing a configuration of a switching power supply unit according to still another embodiment of the present invention. Switching power supply 70 shown in FIG.
Is a switching power supply device 70 shown in FIG.
11 except that the output side load state detection circuit 15 is provided in parallel with the output voltage detection circuit 14 provided between the output side main terminal 17a and the output side sub-terminal 17b. It is similar.

The operation of the switching power supply having such a configuration is the same as that of switching power supply 70 shown in FIG. 11, and therefore operates in the same manner as the time chart shown in FIG.

<Embodiment 16> FIG. 22 is a circuit diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. Switching power supply 70 shown in FIG.
The switching power supply device shown in FIG. 13 includes an output-side load state detection circuit 1
5 is provided in parallel with the output voltage detection circuit 14 provided between the output-side main terminal 17a and the output-side sub-terminal 17b. Other configurations are the same as those of the switching power supply 70 shown in FIG.

The switching power supply 7 having such a configuration
The operation of 0 is the same as that of the switching power supply 70 shown in FIG.

<Embodiment 17> FIG. 23 is a circuit diagram showing a configuration of a switching power supply device according to still another embodiment of the present invention. Specifically, in switching power supply device 70 shown in FIG. Side load state detection circuit 15
Is different from the output voltage detection circuit 14 provided between the output-side main terminal 17a and the output-side sub-terminal 17b only in that the output voltage detection circuit 14 is provided in parallel. It is similar to the device 70. Therefore, a power MOSFET is used as the smoothing capacitance changeover switch 6 provided in the input side smoothing circuit 5.

The switching power supply 7 having such a configuration
The operation of 0 is the same as that of the switching power supply 70 shown in FIG.

<Embodiment 18> FIG. 24 is a circuit diagram showing a configuration of a switching power supply device according to still another embodiment of the present invention. Specifically, in switching power supply device 70 shown in FIG. Side load state detection circuit 15
However, the only difference is that it is provided in parallel with the output voltage detection circuit 14 provided between the output-side main terminal 17a and the output-side sub-terminal 17b. Other configurations are the same as those of the switching power supply device 70 shown in FIG. Therefore,
The input-side smoothing circuit 5 includes a first capacitor C1 connected in parallel with the rectifier circuit 4, and a smoothing capacitance changeover switch 6 and a second capacitor C2 connected in parallel with the first capacitor C1. And a series circuit.

The operation of the switching power supply having such a configuration is the same as that of switching power supply 70 shown in FIG.

<Embodiment 19> FIG. 25 is a circuit diagram showing a configuration of a switching power supply device according to still another embodiment of the present invention. Specifically, in switching power supply device 70 shown in FIG. Side load state detection circuit 15
Are provided in parallel with the output voltage detection circuit 14 provided between the output-side main terminal 17a and the output-side sub-terminal 17b.
Therefore, the primary winding 1a provided on the input side of the transformer 1
Further, an inductance changeover switch 37 for switching the input side inductance of the transformer based on the output of the output side load state detection circuit 15 is provided. Other configurations are the same as those of the switching power supply device 70 shown in FIG.

The operation of the switching power supply having such a configuration is the same as that of the switching power supply shown in FIG. 16, and therefore operates based on the time chart shown in FIG.

<Embodiment 20> FIG. 26 is a circuit diagram showing a configuration of a switching power supply unit according to still another embodiment of the present invention. Specifically, a positive step-down type chopper system shown in FIG. In the switching power supply 70 of
The output side load state detection circuit 15 is provided in parallel with the output voltage detection circuit 14 provided between the output side main terminal 17a and the output side sub-terminal 17b. Therefore, the control circuit 10 and the switching element 9 are integrally formed as a semiconductor device 23, and the output-side load state detection circuit 15 is configured separately from the semiconductor device 23. Other configurations are
This is the same as the switching power supply 70 shown in FIG.

The switching power supply 70 of the positive step-down type chopper type shown in FIG. 26 also has the CONTR of the control circuit 10 similarly to the switching power supply 70 shown in FIG.
When the switching element 9 is turned on, the reference potential Vc1 of the OL terminal voltage Vc increases by the input voltage Vin,
When the switching element 9 is off, the input side voltage Vin is not applied. For this reason, the output voltage detection circuit 14 detects the output voltage Vout only when the switching element 9 is in the off state. Then, on / off control of the switching element 9 is performed based on the output voltage Vout detected by the output voltage detection circuit 14.

The switching power supply 7 having such a configuration
The operation of 0 is the same as that of the switching power supply device 70 shown in FIG. 18, and therefore operates based on the time chart shown in FIG.

<Embodiment 21> FIG. 27 is a circuit diagram showing a configuration of a switching power supply according to still another embodiment of the present invention. More specifically, FIG. In the switching power supply 70 of
The output-side load state detection circuit 15 is provided in parallel with the output voltage detection circuit 14 provided between the output-side main terminal 17a and the output-side sub-terminal 17b. Therefore, the control circuit 10 and the switching element 9 are integrally formed as a semiconductor device 23, and the output-side load state detection circuit 15 is configured separately from the semiconductor device 23. Other configurations are the same as those of the switching power supply device 70 shown in FIG.

The switching power supply 70 of the negative polarity step-down type chopper type shown in FIG. 27 is similar to the switching power supply 70 shown in FIG.
When the switching element 9 is turned on, the reference potential Vc1 of the OL terminal voltage Vc increases by the input voltage Vin,
When the switching element 9 is off, the input side voltage Vin is not applied. For this reason, the output voltage detection circuit 14 detects the output voltage Vout only when the switching element 9 is in the off state. Then, on / off control of the switching element 9 is performed based on the output voltage Vout detected by the output voltage detection circuit 14.

The switching power supply 7 having such a configuration
The operation of 0 is the same as that of the switching power supply 70 shown in FIG.

Although an N-channel MOS transistor is used as the switching element 9,
An N-channel transistor such as a GBT or an NPN transistor may be used.

In each of the above embodiments, the on-resistance of the switching element 9 is the overcurrent level detection resistance of the overcurrent protection function. However, a voltage drop element such as a resistor is connected to the switching element 9 in series. The overcurrent protection function may be configured by using a voltage drop element as a detection resistor. Moreover,
A circuit block or the like for the overload protection function and the overheating protection function of the switching device may be provided.

[0252]

According to the switching power supply of the present invention, the output side load state detecting circuit for detecting the output side load state and the smoothing capacity of the input side power supply circuit based on the output side load state are provided. When an input-side smoothing circuit for switching is provided, and the load connected to the output-side terminal is in a standby state,
Since the input voltage to the switching element is reduced, power consumption of the switching element can be reduced. Further, since the ON / OFF control of the switching element is performed only when the input voltage becomes equal to or lower than the predetermined voltage, power consumption by the switching element can be further reduced.

The switching power supply unit further includes an output-side load state detection circuit, an input-side smoothing circuit for switching an input-side smoothing capacity in accordance with an output signal of the output-side load state detection circuit, and switching means therefor. In the standby state, when the output side load state detection circuit detects that the load is in the standby state, the smoothing capacity of the input side smoothing circuit is reduced, and the input voltage becomes lower than a predetermined voltage. ON / OFF control of the switching element by the control circuit is performed only when the power supply is ON. As a result, it is possible to reduce the power loss in the switching element due to the reduction of the number of times the switching element is turned on and off, and to realize the effect of reducing the power loss in the switching element due to the decrease in the input voltage when the switching element is turned on. Further, power consumption on the input side can be further reduced as compared with the conventional switching power supply device, and the efficiency of the switching power supply can be increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an example of an embodiment of a switching power supply device of the present invention.

FIG. 2 is a time chart showing an operation of the switching power supply device.

FIG. 3 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 4 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 5 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 6 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 7 is a time chart showing an operation of the switching power supply device.

FIG. 8 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 9 is a time chart showing the operation of the switching power supply device.

FIG. 10 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 11 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 12 is a time chart showing the operation of the switching power supply device.

FIG. 13 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 14 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 15 is a time chart showing an operation of the switching power supply device.

FIG. 16 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 17 is a time chart showing the operation of the switching power supply device.

FIG. 18 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 19 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 20 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 21 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 22 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 23 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 24 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 25 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 26 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 27 is a circuit diagram showing a configuration of another example of the embodiment of the switching power supply device of the present invention.

FIG. 28 is a circuit diagram showing a configuration of a conventional switching power supply device.

FIG. 29 is a time chart showing the operation of the switching power supply device.

FIG. 30 is a circuit diagram showing a configuration of another example of a conventional switching power supply device.

FIG. 31 is a time chart showing the operation of the switching power supply device.

[Description of Signs] 1 Transformer 1a Primary winding 1b Secondary winding 1c Auxiliary winding 2 AC power supply 3 Filter 4 Input side rectifier circuit 5 Input side smoothing circuit 6 Smoothing capacitance changeover switch 7 Input voltage detecting circuit 7a Comparator 8 Snubber circuit 9 Switching element 10 Control circuit 11 Capacitor for power supply of control circuit 12 Output rectifier circuit 13 Output side smoothing circuit 14 Output voltage detection circuit 14a Light emitting element 14b Photodiode 15 Output side load state detection circuit 17a Output side main terminal 23 Semiconductor device Reference Signs List 24 Rectifier element 30 Overcurrent detection circuit 31a Overheat protection circuit 31b Overvoltage protection circuit 31c Restart trigger circuit 45 Load 50 Input side power supply circuit 55 Output DC conversion means 60 Output side power supply circuit 70 Switching power supply device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H730 AA14 AS01 BB13 BB15 BB43 BB57 CC01 DD04 DD41 EE02 EE07 FD01 FD11 FD24 FD26 FD41 FF19 FG05 VV01 XX15 XX19 XX26 XX29 XX31 XX38 XX43

Claims (29)

[Claims] An input-side rectifier circuit for rectifying an AC voltage output from an AC power supply, an input-side smoothing circuit for smoothing an output voltage of the input-side rectifier circuit, and a DC output from the input-side smoothing circuit. An input voltage detection circuit for detecting the input side voltage of the input side, a switching element to which the input side voltage is applied, and an input side power supply circuit provided with a control circuit for controlling on / off of the switching element; A switching power supply device comprising: an output-side power supply circuit provided with an output DC conversion means for outputting a DC voltage obtained by rectifying and smoothing a voltage formed by the control to a predetermined load, wherein the load is An output side load state detection circuit for detecting that the load is in a load fluctuation state or a standby state is provided, and the output side load state detection circuit detects that the load is in a standby state. Is detected, the smoothing capacity of the input side smoothing circuit is reduced, and only when the input side voltage output from the input side smoothing circuit is lower than a predetermined value, the switching element A switching power supply device that performs on / off control of the switching power supply. 2. A primary winding of a transformer is provided between an input-side smoothing circuit of the input-side power supply circuit and a switching element, and an output of a secondary winding of the transformer is supplied to the output DC converting means. The switching power supply device according to claim 1, wherein 3. In the standby state, the transformer includes:
3. The switching power supply according to claim 2, further comprising a switch for reducing an input-side inductance when an output voltage output from the output DC converter to the load becomes lower than a predetermined reference voltage. 4. The input-side smoothing circuit is provided with a smoothing capacity changeover switch for reducing a smoothing capacity.
2. The switching power supply device according to claim 1, wherein the smoothing capacity changeover switch is switched by the output side load state detection circuit. 5. The smoothing capacitance changeover switch is a MOSF
5. The switching power supply according to claim 4, wherein the switching power supply is configured by ET. 6. An output voltage output from said output DC conversion means is detected by an output voltage detection circuit provided in said output side power supply circuit, and the detection result of said output voltage detection circuit is 2. The switching power supply according to claim 1, wherein the feedback is fed back to the input side power supply circuit by a feedback circuit. 7. The switching power supply according to claim 6, wherein on / off control of the switching element is stopped based on a detection result of the output voltage detection circuit. 8. A period during which the on / off control of the switching element is stopped changes continuously based on a change in output voltage detected by the output voltage detection circuit.
A switching power supply device according to claim 1. 9. The switching power supply according to claim 6, wherein the feedback circuit is configured to use an optical signal. 10. The switching power supply according to claim 9, wherein the feedback circuit is constituted by a photocoupler. 11. The switching power supply according to claim 6, wherein said output voltage detection circuit is constituted by a Zener diode. 12. The switching power supply according to claim 1, wherein the control circuit is provided with a control circuit power supply capacitor serving as a power supply for the control circuit. 13. The control circuit and the switching element are constituted by a semiconductor device provided on the same substrate, and the semiconductor device has a high potential side terminal and a low potential side terminal of the switching element connected to each other. A pair of terminals, a terminal to which a detection result of the output side load state detection circuit is input, a terminal to which the control circuit power supply capacitor is connected, and a DC input side voltage output from the input side smoothing circuit. The switching power supply device according to claim 12, further comprising five external terminals each including a terminal to which a detection result is input. 14. The switching power supply device according to claim 1, wherein the input-side power supply circuit is provided with a snubber circuit for absorbing noise generated by on / off control of a switching element. 15. The switching power supply device according to claim 1, wherein the control circuit is provided with overcurrent protection means for stopping on / off control of a switching element by an overcurrent to the control circuit. 16. The switching power supply according to claim 1, wherein the control circuit is provided with overheat protection means for stopping on / off control of the switching element when the control circuit is overheated. 17. The switching power supply device according to claim 1, wherein a DC voltage having an absolute value lower than a DC voltage output from the input-side smoothing circuit is output from the output-side power supply circuit. 18. A reference potential of a power supply voltage of the control circuit is higher than a reference value of an output voltage from the output side power supply circuit, and the output voltage is detected regardless of ON / OFF of a switching element. The switching power supply device according to claim 17. 19. The control circuit according to claim 1, wherein a reference potential of a power supply voltage of the control circuit is higher than a reference value of an output voltage from the output side power supply circuit, and the output voltage is set while the switching element is off. The switching power supply according to claim 17, which is detected. 20. An input-side voltage output from the input-side smoothing circuit is 100 V or more, and an absolute value of a DC voltage output from the output-side power supply circuit is 25 V or less.
A switching power supply device according to claim 1. 21. The switching power supply according to claim 17, wherein the DC voltage output from the output-side power supply circuit has a positive polarity or a negative polarity. 22. The control circuit is provided with a control circuit power supply capacitor used as a power supply for the control circuit,
A DC voltage output from the output side power supply circuit is detected by an output voltage detection circuit provided in the output side power supply circuit, and an output terminal of the output side power supply circuit is connected to the control circuit power supply capacitor. The switching power supply device according to claim 17. 23. The switching power supply according to claim 1, wherein an on-time in the on-off control of the switching element is controlled based on an output voltage output from the output DC converter. 24. A control circuit in which an auxiliary winding to which energy is applied via the transformer is provided in the input-side power supply circuit, and an output from the auxiliary winding is rectified and charged in the control circuit. A power supply capacitor is provided as a power supply for the control circuit, and a current supplied from the auxiliary winding to the control circuit power supply capacitor is controlled based on an output voltage output from the output DC converter. Item 24. The switching power supply device according to item 23. 25. An output voltage output from the output DC converting means is detected by an output voltage detection circuit provided in the output side power supply circuit, and a detection result of the output voltage detection circuit is 25. The switching power supply according to claim 24, wherein the feedback is fed back to the input side power supply circuit by a feedback circuit. 26. The switching power supply according to claim 25, wherein the feedback circuit is configured to use an optical signal. 27. The output-side load state detection circuit detects the load fluctuation state or the standby state of the load based on an output voltage output from the output DC conversion unit to the load. The switching power supply device according to claim 24, wherein the switching power supply device is provided in a side power supply circuit. 28. The output-side load state detection circuit is provided in the input-side power supply circuit so as to detect a load fluctuation state or a standby state of the load based on a voltage of the control circuit power supply capacitor. Item 25. The switching power supply device according to item 24. 29. The control circuit and the switching element are constituted by a semiconductor device provided on the same substrate, and the semiconductor device has a high potential side terminal and a low potential side terminal of the switching element connected thereto, respectively. A pair of terminals, a terminal to which the control circuit power supply capacitor is connected, a terminal for outputting a detection result of the output side load state detection circuit, and a terminal for receiving a detection result of the input voltage detection circuit 29. The switching power supply according to claim 24, further comprising five external terminals.