JP3215273B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type stabilized DC power supply having an AC input.

[0002]

2. Description of the Related Art FIG.
1 shows a configuration example of a switching power supply proposed in US Pat. In FIG. 20 is a commercial AC power supply, 21
Is a full-wave rectifier composed of diodes 22, 23, 24 and 25. Reference numeral 26 denotes an inductor, and 27 denotes a transformer, which comprises a primary winding 28, a secondary winding 29, a tertiary winding 30, and a control winding 31. 32 is a smoothing capacitor, 33
Is a switch element, 34 is a rectifying / smoothing circuit and a diode 3
5, a capacitor 36. 37 is a load,
38 is a control circuit.

The circuit operation of this switching power supply is performed by rectifying the input of a commercial AC power supply 20 with a full-wave rectifier 21 and smoothing the input with a smoothing capacitor 32 into a DC having little ripple, and then setting a switch element 33 at a frequency higher than the input commercial AC frequency. To turn on and off, an AC voltage is applied to the primary winding 28 of the transformer 27, and its output is applied from the secondary winding 29 of the transformer 27 to the rectifying and smoothing circuit 34 for rectifying and smoothing. When the switch element 33 is turned off in the basic operation given to the load as
6 flows into the smoothing capacitor 32 via the control winding 31 of the transformer 27, and simultaneously flows through the control winding 31 of the transformer 27. As a result, a corresponding current flows from the tertiary winding 30 of the transformer 27 to the control circuit. 38, and controls the switch element 33. That is, while the switch element 33 is turned off by such a current flow, the energy stored in the inductor 26 is transferred to the smoothing capacitor 32.
Is transmitted to the control circuit 38, and a high power factor and high efficiency switching power supply can be obtained as compared with the conventional switching power supply.

The specific circuit configuration of the control circuit 38 in this circuit comprises an output voltage detector 51, a photocoupler 52, and a control IC 50 as shown in FIG. 10, and when the output voltage exceeds a prescribed voltage, the photocoupler 52 Is turned on, the control IC 50 turns off the switch element 33, and the transformer 2
7 is completely supplied to the secondary winding 29, the polarity of the transformer 27 is inverted, and the tertiary winding 30 is turned off.
The switch IC 33 is turned on when the control IC 50 detects the negative trigger.

[0005]

However, in the circuit configuration of the conventional switching power supply described above, the amount of charge flowing from the control winding 31 increases more than the amount of charge discharged from the smoothing capacitor 32 at light load, The voltage of the smoothing capacitor 32 increases. For this reason, the smoothing capacitor 32 requires a capacitor with a high withstand voltage, and the voltage applied to the switch element 33 also increases. Therefore, the switch element 33 also requires an element with a high withstand voltage. Therefore,
In general, a switch element having a high withstand voltage has a larger loss during current conduction than a switch element with a low withstand voltage, and thus has a problem in that the overall efficiency is reduced. The present invention has been made in view of the above points, and prevents a size increase by suppressing the voltage of the smoothing capacitor 32 even under a condition of a high input voltage or a light load, and increases the size and loss of the switch element 33. An object of the present invention is to provide a small and highly efficient AC input switching power supply by avoiding the increase.

[0006]

SUMMARY OF THE INVENTION A switching power supply according to the present invention comprises a full-wave rectifier connected to an AC power supply, a smoothing capacitor connected between output terminals of the full-wave rectifier, and a terminal connected to the smoothing capacitor. A series circuit of a connected primary winding of a transformer and a switch element; a series circuit of an inductor connected between the full-wave rectifier and the smoothing capacitor; and a control winding of the transformer; A rectifying / smoothing circuit connected to the next winding and having an output terminal connected to a load; and an output voltage of the rectifying / smoothing circuit connected between the output terminal of the rectifying / smoothing circuit and the switch element, the output voltage being a predetermined voltage. in the switching power supply and a control circuit for controlling the switching element so that, provided with a tertiary winding for generating a negative trigger to the transformer, wherein the control circuit before A smoothing capacitor voltage detection unit for detecting the voltage of the smoothing capacitor, On'o of the switching element
Control IC for controlling the operation of the switch, the control IC and the tertiary winding
A parallel circuit of high resistance and low resistance provided between
The low resistance of the parallel circuit is inserted or removed from the parallel circuit.
Both the second switch element to be removed and the control IC
A delay circuit consisting of a capacitor connected to the end
In addition, the smoothing capacitor voltage detecting section includes the smoothing capacitor.
When the voltage of the sensor detects a predetermined voltage or more, the second
The low resistance is released by a switch element,
From the next winding to the control IC via the high resistance.
Delays the operation of the switch element.
It is intended to be extended .

[0007]

FIG. 1 shows an embodiment of the present invention. The same parts as those of the conventional example shown in FIG. 9 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 1, reference numeral 42 denotes a control circuit, and FIG. 5 shows a principle diagram thereof. This control circuit 42 is obtained by adding a smoothing capacitor voltage detector 53 and a delay circuit 54 to the conventional control circuit 38 shown in FIG. In the operation, the delay circuit 54 detects the voltage of the smoothing capacitor 32 by the smoothing capacitor voltage detector 53 and sets the delay time by which the negative trigger of the tertiary winding 30 is transmitted to the control IC 50 so that the voltage becomes a specified voltage. It is to control. As a specific example of the control circuit 42, as shown in FIG. 6, an output voltage detector 51, a photocoupler 52, a control I
C50, a smoothing capacitor voltage detector 53 provided with a comparator 61, resistors 62 and 63, and a delay circuit 54 provided with a diode 55, a resistor 56, an FET 57, a diode 58, a resistor 59, and a capacitor 60. .

Next, the operation of the switching power supply of FIG. 1 together with the control circuit 42 of FIG. 6 will be described. When the output voltage of the rectifying / smoothing circuit 34 exceeds a specified voltage, the output voltage detector 51 detects this and makes the photocoupler 52 conductive, and the control IC
50 turns off the switch element 33. The energy stored in the transformer 27 due to this OFF operation is transferred to the secondary winding 2.
9, the tertiary winding 30 of the transformer 27
Is inverted. At this time, if the voltage of the smoothing capacitor 32 is lower than the specified value, the smoothing capacitor voltage detecting section 53 turns on the FET 57. Therefore, the tertiary winding 3
The negative trigger of 0 discharges the capacitor 60 through the diode 58 and the resistor 59 set to a low resistance, so that the input of the control IC 50 as a negative trigger is almost delayed with respect to the reversal of the tertiary winding 30. I do. FIG. 7A shows the operation waveform of the switch element 33 at this time.

On the other hand, when the voltage of the smoothing capacitor 32 is higher than a prescribed value, the smoothing capacitor voltage detector 53 turns off the FET 57. Therefore, the negative trigger of the tertiary winding discharges the capacitor 60 through the resistor 56, which is set to a high resistance, thereby providing a control IC.
The input of 50 as a negative trigger is delayed with respect to the reversal of the tertiary winding 30. As a result, the ON of the switch element 33 is delayed, and the voltage of the smoothing capacitor 32 decreases. FIG. 7B shows the operation waveform of the switch element 33 at this time. In order to keep the smoothing capacitor 32 at a specified voltage, the smoothing capacitor voltage detector 53 needs to control the FET 57 in the active region. FIG. 8 shows the voltage of the smoothing capacitor 32 with respect to the load capacitance (output current) in FIG. 1 shown as a circuit according to an embodiment of the present invention and that in FIG. 9 shown as a conventional circuit example in correspondence. As apparent from FIG. 8, the switching power supply using the control circuit 42 of the present invention can control the voltage of the smoothing capacitor 32 to a specified value or less while maintaining the constant voltage of the output voltage. .

FIGS. 2 to 4 are circuit diagrams of another embodiment of the present invention. The operation thereof can be obtained by using the control circuit shown in FIG. 5 or FIG. In the embodiment shown in FIG. 2, a capacitor 39 is provided between the inductor 26 of the embodiment shown in FIG. 1 and the control winding 31 of the transformer 27, and is connected in parallel to a series circuit of the capacitor 39 and the control winding 31. The diode 40 is provided. The operation of this circuit is as follows. When the switch element 33 is on, the current of the inductor 26 flows through the control winding 31 and the primary winding 28 of the transformer 27 via the capacitor 39 and the switch element 33. Start to have voltage,
When the voltage becomes higher than the voltage of the smoothing capacitor 32,
The current of the inductor 26 flows into the smoothing capacitor 32 through the diode 40. Therefore, the boosting time of the inductor 26 is shortened even though the switch element 33 is turned on. This has the effect of shortening the boosting time as the input voltage increases.

When the switch element 33 is off, the current of the inductor 26 flows into the smoothing capacitor 32 via the diode 40, and at the same time, the transformer 27
The excitation current from the control winding 31 flows through the capacitor 39 and the diode 40, and the capacitor 39 is charged in the opposite direction to the ON period of the switch element 33, and the voltage drops. That is, in this embodiment, the boosting time of the inductor 26 becomes shorter as the input voltage becomes higher.
In the continuous mode in which the current does not return to zero amperes while the switch element 33 is off, the input current waveform substantially corresponds to a sine wave, and the power factor increases.

In the embodiment shown in FIG. 3, a capacitor 41 is connected between both terminals of the switch element 33 of the embodiment shown in FIG. The operation of this circuit is performed after the exciting current of the transformer 27 is reset to zero amperes while the switch element 33 is off, before the exciting inductance of the transformer 27 and the capacitor 41 resonate, and before the switch element 33 is turned on. Since the voltage between the terminals of the switch element 33 is reduced to near zero volts,
The switching loss at the time of ON can be reduced. The embodiment of FIG. 4 corresponds to FIG.
And both the changes of the embodiment of FIG. 3 are provided.
The function has both functions and effects.

[0013]

As described above, the voltage of the smoothing capacitor 32 is set low even under a high input voltage or a light load condition by changing the timing at which the switch element 33 is turned on while leaving the conventional main circuit as it is. Therefore, the smoothing capacitor 32 can have a low withstand voltage, and the switch element 33 can have a low withstand voltage and a small on-resistance. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of another embodiment of the present invention.

FIG. 5 is a principle diagram of a control circuit according to the present invention.

FIG. 6 is a control circuit diagram of one embodiment of the present invention.

FIG. 7 is an operation waveform diagram of the switch element 33 according to the present invention.

FIG. 8 is a comparison diagram of voltage characteristics of a smoothing capacitor 32 of the present invention and a conventional example.

FIG. 9 is a conventional circuit diagram.

FIG. 10 is a conventional control circuit diagram.

[Explanation of symbols]

Reference Signs List 20 commercial AC power supply 21 full-wave rectifier 22, 23, 24, 25, 35, 40, 55, 58 diode 26 inductor 27 transformer 28 primary winding of transformer 29 secondary winding of transformer 30 tertiary winding of transformer 31 Control winding 32 Smoothing capacitor 33 Switch element 34 Rectifying smoothing circuit 36, 39, 41, 60 Capacitor 37 Load 38, 42 Control circuit 50 Control IC 51 Output voltage detector 52 Photocoupler 53 Smoothing capacitor voltage detector 54 Delay circuit 56 , 59, 62, 63 resistor 57 FET 61 comparator

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kiyoshi Terasawa 10-13 Minamicho, Hanno-shi, Saitama Shindengen Kogyo Co., Ltd. (72) Inventor Haruo Watanabe 10-13 Minamicho, Hanno-shi, Saitama Shindengen Kogyo Co., Ltd. (56) References JP-A-3-265462 (JP, A) JP-A-6- 261543 (JP, A) JP-A-60-174067 (JP, A) JP-A-4-76185 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/06 H02M 3 / 28 H02M 7/217

Claims (3)

(57) [Claims] 1. A full-wave rectifier connected to an AC power supply, a smoothing capacitor connected between output terminals of the full-wave rectifier, a primary winding and a switching element of a transformer connected between terminals of the smoothing capacitor. A series circuit of an inductor connected between the full-wave rectifier and the smoothing capacitor and a control winding of the transformer, and an output terminal connected to a secondary winding of the transformer and And a control connected between the output terminal of the rectifying / smoothing circuit and the switch element to control the switching element so that the output voltage of the rectifying / smoothing circuit becomes a predetermined voltage. in the switching power supply having a circuit, provided with a tertiary winding for generating a negative trigger to the transformer, the said control circuit smoothing sensing the voltage of the smoothing capacitor Conde And differential voltage detecting unit, said switch element
A control IC for controlling the on / off operation of the child,
Average of high resistance and low resistance provided between the tertiary winding
Column circuit, the low resistance of the parallel circuit with respect to the parallel circuit
A second switch element to be inserted or removed, and
Delay consisting of capacitors connected to both ends of your IC
And a smoothing capacitor voltage detecting unit,
When the voltage of the smoothing capacitor is detected to be higher than the specified voltage
Release the low resistance by the second switch element.
And the control IC from the tertiary winding via the high resistance.
The negative trigger given to the
A switching power supply characterized in that the operation of the switching power supply is delayed . 2. A capacitor provided between the inductor and a control winding of the transformer, and a diode provided in parallel with a series circuit of the capacitor and the control winding. Switching power supply. 3. The switching power supply according to claim 1, further comprising a capacitor provided between both terminals of said switch element.