JP3191756B2 - 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 power supply, and more particularly, to a switching power supply having a control system with good stability even under light load and heavy load.

[0002]

2. Description of the Related Art Generally, a PWM method (pulse width) is used.
The switching power supply device of the present invention connects a switching element to a primary winding of a high-frequency transformer (hereinafter simply referred to as a transformer) to which DC power is supplied, and turns on and off the switching element to perform rectification and smoothing on a secondary side. A stable DC voltage is obtained, and this DC voltage is applied to a load.

The above-mentioned secondary DC voltage actually fluctuates constantly following the state of the load. For example, when the load is heavy, the secondary DC voltage decreases with respect to the rated output voltage. It rises at light load. For this reason, while detecting the state of the DC voltage on the secondary side, the on / off period of the switching element is controlled so as to always obtain the rated output voltage on the secondary side.

For example, under heavy load, the amount of current induced on the secondary side is increased by controlling the ON width of the switching element to increase the DC voltage to approach the rated output voltage.

On the other hand, at the time of light load, the amount of current induced on the secondary side is reduced by controlling the ON width of the switching element to be narrow, and the DC voltage is lowered so as to approach the rated output voltage. A constant DC voltage is obtained.

[0006] Such control methods include a voltage mode control method and a current mode control method. The configuration of the switching power supply of the voltage mode control system and the current mode control system will be described below.

FIG. 6 is a schematic configuration diagram of a switching power supply of a voltage mode control system. As shown in FIG. 6, the switching power supply of the voltage mode control system connects input terminals 1 and 2 of a rectifying / smoothing circuit section 3 to a commercial AC power supply, and connects transformers to output terminals 3a and 3b of the rectifying / smoothing circuit section 3. 4, a first series circuit 6 including a primary winding 5 and a switching element Q1 is connected in series. Further, the transformer 4 has an auxiliary winding 7, a diode 8 and a capacitor 9 are connected to the auxiliary winding 7, and a driving point of a control circuit unit described later is connected to a connection point A between the capacitor 9 and the cathode of the diode 8. Obtain power supply. The other end of the resistor R2, one end of which is connected to one end 5a of the primary winding 5, is connected to the connection point A.

On the other hand, on the secondary side, a diode 11 and a capacitor 12 are connected to the secondary winding 10, and one end 14 of a load 13 is connected to a connection point between the capacitor 12 and the cathode of the diode 11.

The connection point on the secondary side has a detection point C
And a detection circuit unit 1 for detecting, via an input terminal 18a, a DC voltage obtained from the detection point C to the secondary side.
8 are provided.

Further, on the primary side, a triangular wave signal is generated and a power MOSF is generated based on a detection voltage of the detection circuit section 18.
A control signal (hereinafter referred to as a drive signal) having a predetermined duty ratio is applied to a gate G of the ET (hereinafter simply referred to as a switching element Q1).
And a control circuit section 20 for outputting ON and OFF of the switching element Q1.

The control circuit unit 20 is driven by an input terminal 20a for inputting a driving power supply at a connection point A, an input terminal 20b connected to an output terminal 18b of the detection circuit unit 18, and a gate G of the switching element Q1. Output end 20 for sending out signal
c, the source S of the switching element Q1 and the capacitor 9
Output terminal 20 commonly connected to the other end of the auxiliary winding 7, the other end 7 b of the auxiliary winding 7, the other output end 3 b of the rectifying / smoothing circuit section 3, and the ground.
d is provided.

As shown in FIG. 7, the control circuit section 20 includes a regulator circuit 21 for generating a constant reference voltage using a driving power supply for an input terminal 20a, and a linear circuit from the lowest voltage to the highest voltage with time. Triangular wave signal V8 that repeatedly rises and falls linearly with time to the lowest voltage, and a rectangular wave pulse wave for determining the dead time of a drive circuit described later in synchronization with the triangular wave signal V8 An oscillator (OSC) 22 for outputting V9 (hereinafter referred to as a triangular wave synchronization pulse signal V9);
Resistors R3 and R4 for obtaining a control voltage V7 obtained by dividing the reference voltage from 1 at a voltage dividing point B.

A comparator 23 outputs an output signal V10 obtained by comparing the triangular wave signal V8 from the oscillator 22 with the control voltage V7. An output signal V10 from the comparator 23 is supplied to a reset terminal R. Input triangular wave synchronization pulse signal V9 to set terminal S

Then, a flip-flop 24 for obtaining a logical output signal, a triangular wave synchronizing pulse signal V9 and a logical output signal from the flip-flop 24 are input to an output terminal (hereinafter, simply referred to as an output terminal Q bar). A NOR circuit 25 that outputs a logical sum (inversion) of these, and a drive circuit 26 that outputs a drive signal V11 for driving the switching element Q1 to the gate G based on the logical sum (inversion) from the NOR circuit 25 Have.

On the other hand, as shown in FIG. 7, the detection circuit section 18 includes resistors R5 and R6 for obtaining a DC voltage at a detection point C on the secondary side at a voltage dividing point D, a DC voltage at the voltage dividing point D and a reference voltage. The output level based on the difference from the voltage source 27
And a differential amplifier 28 for controlling The collector of the photocoupler 29 is connected to the input terminal 20b of the control circuit unit 20.
To the partial pressure point B via

That is, the DC voltage Vo obtained on the secondary side
The detection circuit unit 18 inputs the detection voltage of ut as a feedback signal, and the control voltage V7 fluctuates according to the difference between the voltage level of the feedback signal and the reference voltage.

The operation of the switching power supply of the voltage mode control system configured as described above will be described below. FIG. 8 is a timing chart illustrating the operation of the voltage mode switching power supply.

When the input terminals 1 and 2 are connected to a commercial AC power supply, the AC is rectified and smoothed by the rectifying and smoothing circuit section 3.
The DC obtained by the rectifying / smoothing circuit 3 is connected to the resistor R
2 and a capacitor 9 in a second series circuit,
A control power supply of a predetermined voltage is obtained at the connection point A. The control power is input to the control circuit unit 20 via the input terminal 20a of the control circuit unit 20. The control circuit unit 20 operates in response to the input of the control power supply, turns on and off the switching element Q1 to generate a DC pulse in the primary winding 5, and to control the secondary winding 10 based on both winding ratios. An AC pulse is induced to obtain a DC voltage smoothed and rectified by the diode 11 and the capacitor 12.

The operation of the control circuit unit 20 at this time will be described in detail below. Regulator circuit 2 of control circuit unit 20
1 obtains a predetermined DC voltage from a driving power supply and
And a third series circuit including resistors R3 and R4.

When the DC voltage is applied, the oscillator 22
Outputs a triangular wave signal V8 of a predetermined frequency to the comparator 23 as shown in FIG. 8, and outputs a triangular wave synchronizing pulse signal V9 for determining the dead time of the drive circuit 26 synchronized with the triangular wave signal V8.

The triangular wave synchronizing pulse signal wave V9 is at the H level during the falling of the triangular wave signal V8. Further, the control voltage signal V7 at the voltage dividing point B fluctuates (at a heavy load and at a light load) depending on the detection voltage detected by the detection circuit unit 18.

The comparator 23 compares the control voltage signal V7 with the triangular wave signal V8. While the triangular wave signal V8 exceeds the voltage of the control voltage signal V7, the output signal V1 at the H level is output.
0 is sent to the reset terminal R of the flip-flop 24.

For this reason, in the flip-flop 24, the triangular wave synchronizing pulse signal V9 is at L level and the output signal V10 is at L level.
An output signal (not shown) in which the output terminal Q is at the H level during the level, and the output terminal Q is at the L level while the triangular wave synchronizing pulse signal V9 is at the L level and the output signal V10 is at the H level.
Get. While the triangular wave synchronizing pulse signal V9 is at the H level and the output signal V10 is at the H level, an H level output signal is obtained at the output terminal Q bar.

The output signal from the flip-flop 24 is output to the drive circuit 26 as an output signal (not shown) inverted by the NOR circuit 25. Drive circuit 26
8 in accordance with the input of the output signal from the NOR circuit 25.
Is sent to the gate G of the switching element Q1.

As shown in FIG. 8, the drive signal V11 goes to the H level as the triangular wave signal V8 rises from the lowest peak voltage. Is repeatedly changed to L level when the output signal V10 becomes H level.

That is, since the on-width of the switching element Q1 is controlled by comparing the triangular wave signal V8 with the control voltage signal V7, the current I4 in the switching element Q1 which performs the switching operation by charging / discharging the gate input capacitance.
Has a stable current waveform I4 in which charging and discharging are performed during one cycle of the driving signal V11 under light load, but under heavy load, the driving signal is compared with the triangular wave signal V8 and the control voltage signal V7. Since the duty width of V11 is determined, the peak of the current I4 in the switching element Q1 becomes larger than at the time of light load.

In particular, in such a state, an oscillation state may occur as shown in FIG. 8, and the state controls the DC voltage on the secondary side, which is the output of the power supply, for two or more cycles. Unstable operation often occurred. In such a case, the phase correction of the control system has been performed.

Next, the current mode control method will be described. FIG. 9 is a schematic configuration diagram of a current mode switching power supply device.

As shown in FIG. 9, the switching power supply of the current mode control system has one end of a resistor R1 connected to a source S of a switching element Q1 and a connection point F between the switching element Q1 and the resistor R1. The input terminal 30e of the control circuit unit 30 described later is connected. Also, the resistor R1
Is commonly connected to the output terminal 3b of the rectifying / smoothing circuit unit 3.

That is, a series circuit (hereinafter, referred to as a third series circuit) including the primary winding 5, the switching element Q1, and the resistor R1 is connected to the rectifying / smoothing circuit unit 3.

As shown in FIG. 10, the control circuit section 30 connects the output terminal 30 to the gate G of the switching element Q1.
c, the output terminal 30d is connected to the output terminal 3b of the rectifying / smoothing circuit unit 3, the input terminal 30e is connected to the connection point F of the third series circuit, and the input terminal 30b is described later. It is connected to the detection circuit section 18. Also, the input terminal 30
a is connected to the connection point A.

The control circuit unit 30 includes a regulator circuit 31 similar to that shown in FIG.
A circuit 25 and a drive circuit 26 are provided.

Further, the control circuit section 30 linearly rises from the lowest voltage to the highest voltage with time in accordance with the supply of the DC power from the regulator circuit 31, and decreases linearly with time to the lowest voltage. An oscillator (OSC) 32 that outputs a triangular-wave synchronization pulse signal V14 for determining the dead time of the drive circuit 26 in synchronization with a triangular-wave-shaped voltage waveform V13 that repeats the operation, and a constant current flowing through the regulator circuit 31 The obtained control voltage signal V16 and the voltage signal V at the connection point F of the third series circuit
15 and a comparator 33 for sending the output signal V17 to the reset terminal R of the flip-flop 24 when the voltage signal V15 is equal to or higher than the control voltage.

The operation of the switching power supply of the current mode control system configured as described above will be described below. FIG. 11 is a timing chart illustrating the operation of the current mode switching power supply device.

When the input terminals 1 and 2 are connected to a commercial AC power supply, the AC is rectified and smoothed by the rectifying and smoothing circuit unit 3.
The DC obtained by the rectifying / smoothing circuit 3 is connected to the resistor R
2 and a capacitor 9 in a second series circuit,
A control power supply of a predetermined voltage is obtained at the connection point A. The control power is input to the control circuit unit 30 via the input terminal 30a of the control circuit unit 30. The control circuit unit 30 enters an operating state in response to the input of the control power supply, turns on and off the switching element Q1 to generate a DC pulse in the primary winding 5, and
An AC pulse based on both winding ratios is induced in the secondary winding 10 to obtain a DC voltage smoothed and rectified by the diode 11 and the capacitor 12.

The operation of the control circuit unit 30 at this time will be described below. The regulator circuit 31 of the control circuit unit 30 includes:
A predetermined voltage obtained from the control power supply is applied to the oscillator 32, and a constant current based on the predetermined voltage flows through the resistor R4 and the input terminal (minus) of the comparator 33. The voltage at this time is referred to as a control voltage signal V16.

The oscillator 32 outputs the triangular wave synchronizing pulse signal V14 for determining the dead time of the driving circuit synchronized with the triangular wave signal V13 as shown in FIG.
5 and the set terminal S of the flip-flop 24. The triangular wave synchronizing pulse signal V14 is
13 is at the H level between the falling peaks.

The comparator 33 compares the voltage signal V15 at the connection point F with the control voltage signal V16. When the voltage signal V15 exceeds the control voltage signal V16, the output signal V15 is output.
17 is sent to the reset terminal R of the flip-flop 24.

While the triangular wave synchronizing pulse signal V14 is at the L level and the output signal V17 is at the L level, the flip-flop 24 sets the output terminal Q bar to the H level and the triangular wave synchronizing pulse signal V
While the signal 14 is at the L level and the output signal V17 is at the H level, an output signal (not shown) at the L level at the output terminal Q is obtained. While the triangular wave synchronizing pulse signal V14 is at the H level and the output signal V17 is at the H level, an H level output signal is obtained at the output terminal Q bar.

The output signal from the flip-flop 24 is output to the drive circuit 26 as an output signal (not shown) inverted by the NOR circuit 25. Drive circuit 26
FIG. 1 shows an output signal from the NOR circuit 26 according to the input of the output signal.
1 is sent to the gate G of the switching element Q1.

As shown in FIG. 11, the drive signal V18 becomes H level as the triangular wave signal V13 rises from the lowest voltage. It repeatedly repeats that the output signal V17 goes low when it goes high.

That is, the current in the switching element Q1 which performs the switching operation by charging / discharging the gate input capacitance has a stable current waveform I5 for charging / discharging during one cycle of the drive signal V18 when the load is light. Was.

[0042]

However, in the voltage mode control system, the control voltage V7 (the feedback voltage signal of the output voltage obtained on the secondary side) is used even in an operation state in which the input / output state of the switch power supply does not fluctuate. ) And the output voltage is controlled by controlling the current flowing in the switching element Q1 by controlling the ON period of the Q1 in comparison with the triangular waveform voltage V8. Therefore, the current of the current 14 flowing in the switching element Q1 as shown in FIG. Oscillation states having different peaks are likely to occur. In such a case, the phase correction of the control system must be performed, but there is a problem that it takes time to study. Further, even if the consideration is made sufficiently, the phase correction may not be completed.

On the other hand, in the current mode control method, the peak of the current I5 of the switching element Q1 is detected by the resistor R1 and converted into the voltage V15, and the control voltage V16 (the feedback voltage signal of the output voltage obtained on the secondary side is Yes) and voltage V1
5 is directly compared to control the current peak of the current 15, so that an oscillation state that is likely to occur in the voltage mode control method is unlikely to occur, and a stable operation can be obtained.

However, the voltage signal level (current peak value) for detecting the current flowing through the switching element Q1 cannot be set high to suppress resistance loss.
That is, the control voltage V16 cannot be increased.

For this reason, there is a problem that the voltage V15 has a small noise margin with respect to the control voltage V16, and the operation is likely to be unstable due to the influence of noise particularly at a light load.

In the current mode control method, the switching element Q1 is operated while the continuous inductor current is flowing.
At the time of a heavy load in which the N duty exceeds 50%, as shown in FIG.
(1) A phenomenon in which the ON period fluctuates, a sound is generated from the transformer, and the ripple increases.)
This also resulted in unstable operation.

Since this sub-harmonic phenomenon occurs regardless of the phase of the control system, it must be redesigned when the sub-harmonic phenomenon occurs. Similarly, there was a problem that the examination time was required.

In order to prevent the sub-harmonic phenomenon from occurring, a downslope sawtooth wave is applied to the control voltage V16 or the voltage V15
There is a method to add an up slope (slope) sawtooth, but both methods require a circuit dedicated to countermeasures against subharmonic phenomena, so the circuit increases in complexity and increases the cost of the circuit There was a problem that also became.

The present invention has been made to solve the above-described problems, and a sub-harmonic phenomenon in which the ON duty exceeds 50% occurs at a light load and in a state where a continuous inductor current flows through the switching element Q1. It is an object of the present invention to provide a switching power supply device having a control method with good stability without configuring a circuit dedicated to sub-harmonic measures even in a load state.

[0050]

According to the present invention, there is provided a series circuit of a primary winding and a switching element of a transformer connected between one end and the other end of a DC power supply, and a series connection of a secondary winding of the transformer. Rectifier circuit, an output smoothing circuit connected to the rectifier circuit, a current detection circuit for detecting a current flowing through the switching element, and a signal current corresponding to an error between an output voltage of the output smoothing circuit and a reference voltage. An output voltage detection circuit that performs control to cause a current to flow, and an addition circuit that obtains an addition voltage signal by adding a mirror current of the signal current and a detection current from the current detection circuit to flow through a resistor according to the control. A triangular wave generating circuit that generates a triangular wave signal, and the switching element is turned on in synchronization with the rising or falling of the triangular wave signal, and the added voltage signal obtained from the adding circuit. A control that compares the triangular wave signal obtained from the triangular wave generation circuit and turns off the switching element in synchronization with an output of a comparator that outputs an output signal when the added voltage signal reaches the triangular wave signal. And a control signal forming circuit for generating a signal.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a schematic configuration diagram of a switching power supply according to a first embodiment. FIG.
The switching power supply device shown in (1) adds a voltage corresponding to the DC voltage on the secondary side to a voltage corresponding to the current I3 flowing when the switching element Q1 connected in series to the primary winding 5 on the primary side is turned on and off. By using the current mode method, the stability of the DC voltage generated on the secondary side is improved even under light load and heavy load.

The switching power supply shown in FIG. 1 comprises a rectifying / smoothing circuit 3, a transformer 4, a primary winding 5 of the transformer 4, a switching element Q1 and a resistor R1 similar to the current mode control system shown in FIG. A third series circuit, a second series circuit including a resistor R2 and a capacitor 9, and a diode 8 are provided on the primary side.

On the other hand, on the secondary side, a load 13 connected to the secondary winding 10, a diode 11, and a capacitor 12 are provided. Further, a DC voltage at a detection point C where the cathode of the diode 11 on the secondary side, one end of the capacitor 12 and one end 14 of the load 13 are commonly connected is detected, and this detected value is input to a control circuit unit 40 described later. End 40
b is provided.

Further, as shown in FIG. 1, the control circuit section 40 connects the output terminal 4 to the gate G of the switching element Q1.
0c, and the output terminal 40d is connected to the output terminal 3b of the rectifying and smoothing circuit unit 3, the input terminal 40a is connected to the connection point A, and the input terminal 40b is connected to the detection circuit unit 18. And the input terminal 40e is connected to the connection point F.

As shown in FIG. 1, the control circuit section 40 includes a regulator circuit 21 for supplying a constant current by using a control power supply at the input terminal 40a, and a linear circuit that rises linearly with time from the lowest voltage to the highest voltage. , A triangular wave signal V <b> 1 that repeats a linear decrease with time to the lowest voltage
And a rectangular pulse signal V2 for determining the dead time of the drive circuit 25 in synchronization with the triangular waveform signal V1.
And an oscillation circuit 41 that outputs

Further, the control circuit section 40 has a mirror circuit 43, a buffer amplifier 45, and a resistor Ra, which will be described later, and has a resistor Ra to generate a voltage V4 corresponding to a current I3 flowing through a connection point F between the switching element Q1 and the resistor R1. , DC voltage Vo on the secondary side
and an addition circuit 42 that obtains a voltage V3 (hereinafter referred to as an addition voltage V3) obtained by adding a voltage corresponding to ut.

Further, the control circuit section 40 outputs the triangular wave signal V1.
And the triangular wave synchronizing pulse signal V2 and the addition voltage V3 are input, and from the rising and falling timings of these signals, from the start of the falling of the triangular wave signal V1 to the time when the falling line intersects with the addition voltage V3 is set to the H level. Control signal forming circuit 46 for sending a control signal (hereinafter referred to as drive signal V6) of the duty ratio to be applied to gate G of switching element Q1.
And

FIG. 2 shows a detailed configuration of such a control circuit section 40. As shown in FIG. 2, the oscillation circuit 41 of the control circuit unit 40 connects the constant current circuits I1 and I2 and the transistor Q5 in series, and connects the capacitor C1 in parallel to the series circuit of the constant current circuit I2 and the transistor Q5. Further, in parallel with the series circuit of the constant current circuits I1 and I2 and the transistor Q5,
A series circuit composed of a resistor R6 and a resistor R7 is connected. Further, the oscillation circuit 41 is connected to the regulator circuit 21 via a mirror circuit 43 described later.

Further, a positive input terminal is connected to a connection point between the capacitor C1 and the constant current circuit I2, and resistors R6 and R6 are connected.
Comparator 4 with the negative input terminal connected to the voltage dividing point 7
8 and a transistor Q4 having a collector connected to a negative input terminal of the comparator 48 via a resistor R8 and a base connected to the output of the comparator 48. Also, the comparator 48
Is provided with a transistor Q5 having a base connected to the output and a collector connected to the constant current circuit I2.

Further, the plus input terminal of the comparator 48 is connected to the minus input terminal of the comparator 50 of the control signal forming circuit 46, and the triangular wave synchronizing pulse signal V2 obtained by inverting the output of the comparator 48 is connected. And a NOT circuit 44 for outputting the same.

By connecting these components as described above, the oscillation circuit 41 generates the triangular wave signal V1 at the positive input terminal of the comparator 48 and outputs the triangular wave signal V1 to the output of the comparator 48. Synchronously, a rectangular triangular synchronous pulse wave signal V2 for determining the dead time of the drive circuit 26 is obtained.

The control circuit section 40 includes a buffer amplifier 45 connected to a connection point F between the switching element Q1 and the resistor R1 via an input terminal 40e, one of which is connected to the output terminal of the buffer amplifier 45 and the other is connected to ground. And a connected resistor Ra. The buffer amplifier 45 and the resistor R1 are collectively referred to as current detecting means.

One end of the resistor Ra is commonly connected to the collector of the transistor Q3 of the mirror circuit 43, the positive input terminal of the comparator 50 of the control signal forming circuit 46, and the output terminal of the buffer amplifier 45.

The mirror circuit 43 includes transistors Q2, Q
The collector of the transistor Q3 is commonly connected to one end of the resistor Ra, the positive input terminal of the comparator 50 of the control signal forming circuit 46, and the output terminal of the buffer amplifier 45.

The collector of the transistor Q2 and the bases of the transistors Q2 and Q3 are connected to the collector of the phototransistor Q6 of the photocoupler 29 via the input terminal 40b.

That is, the mirror circuit 43, the buffer amplifier 45, and the addition circuit 42 having the resistance Ra provide the current I flowing through the connection point F between the switching element Q1 and the resistance R1.
3 to the secondary side DC voltage Vou
The added voltage V3 obtained by adding the voltage corresponding to t is obtained at the positive input terminal of the comparator 50 of the control signal forming circuit 46.

As shown in FIG. 2, the control signal forming circuit 46 includes a flip-flop 24, a NOR circuit 25, and a driving circuit 26 similar to those of the conventional control signal forming circuit. A positive input terminal and a negative input terminal of the amplifier 48 are connected, and one end of the resistor Ra, the collector of the transistor Q3 of the mirror circuit 43, and the output terminal of the buffer amplifier 45 are commonly connected to the positive input terminal. And a comparator 50 having an output terminal connected to the reset R of the flip-flop 24.

This comparator 50 outputs an H-level output signal V5 when the addition voltage V3 reaches the falling waveform of the triangular wave signal V1.

The flip-flop 24, the NOR circuit 25, and the drive circuit 26 are configured such that the flip-flop 24 outputs the output signal V5 from the comparator 50 to the reset terminal R,
The pulse signal V2 output from the circuit 44 is input to the set terminal S, and the NOR circuit 25 outputs the
The triangular wave synchronizing pulse signal V2 from the T circuit 44 is input to the other input terminal from the output terminal Q bar of the flip-flop 24, and a logical sum (inversion) of these signals is output to the drive circuit 26. .

That is, the control signal forming circuit 46 outputs the triangular wave signal V1, the triangular wave synchronizing pulse signal V2, and the addition voltage V3.
From the rising and falling timings of these signals, and from the start of the falling of the triangular wave signal V1, to the switching element of the drive signal V6 having a duty ratio that sets the level between the intersection of the falling line and the addition voltage V3 to the H level. The signal is sent to the gate G of Q1.

The operation of the switching power supply configured as described above will be described below. FIG. 3 is a timing chart for explaining the operation under a light load. FIG. 4 is a timing chart for explaining the operation under heavy load.

(Operation at Light Load) When the input terminals 1 and 2 are connected to a commercial AC power supply,
Is rectified and smoothed. Then, the DC voltage Vin obtained by the rectifying / smoothing circuit section 3 is applied to a second series circuit composed of the resistor R2 and the capacitor 9, and a control power of a predetermined voltage is obtained at the connection point A. This control power is input to the control circuit unit 40 via the input terminal 40a of the control circuit unit 40. The control circuit unit 40 enters an operating state in response to the input of the control power supply, turns on and off the switching element Q1 to generate a pulse in the primary winding 5, and supplies an alternating current to the secondary winding 10 based on both winding ratios. A pulse is induced to obtain a DC voltage Vout which is smoothed and rectified by the diode 11 and the capacitor 12.

The operation of the control circuit unit 40 at this time will be described in detail below. Regulator circuit 2 of control circuit section 40
1 is a predetermined voltage (for example, 7 V) obtained from a control circuit power supply
And charges the capacitor C1 of the oscillation circuit 41 with the constant current I1 based on the predetermined voltage. With this charging, the potential of the capacitor C1 starts to rise with a certain slope.

At this time, the output of the comparator 48 is at the L level, the transistors Q4 and Q5 are in the OFF state, and the potential on the minus input side of the comparator 48 is a potential (for example, 4 V) determined by the voltage dividing ratio of R6 and R7. ing. Then, when the potential of the capacitor C1 rises and reaches a potential (for example, 4 V) determined by the voltage dividing ratio of R6 and R7,
The output of the comparator 48 is inverted to H level, and the transistor Q
4 and Q5 are turned on, R8 is connected in parallel with the resistor R7, and the potential on the minus input side of the comparator 48 becomes lower than the potential determined by the voltage division ratio of R6 and R7 (for example, 1 V).

At this time, the constant current I2 having a larger current value than the constant current I1 is discharged from the capacitor C1, and the capacitor C1 starts falling with a constant slope. That is, the capacitor C1 and the comparator 48 form a triangular wave signal V1 shown in FIG. 3 having a fixed frequency by repeating the above operation.

The rectangular wave pulse signal VP appearing at the output of the comparator 48 is synchronized with the triangular wave signal V1 and is at the L level while the triangular wave signal V1 rises.

The pulse VP is output to the NOT circuit 44
The triangular wave synchronizing pulse signal V shown in FIG.
2 (H level while the triangular wave signal V1 is rising)
And is sent to the set terminal S of the NOR circuit 25 and the flip-flop 24. This triangular wave synchronization pulse signal V
The period of the H level of 2 is the dead time.

Therefore, the maximum ON of the switching element Q1
The duty is determined by the ratio between the constant currents I1 and I2 (waveform of V1). It is desirable that the voltage difference between the Hi side and the Low side of the triangular wave be large.

On the other hand, as shown in FIG. 1, the detection circuit section 18 supplies the DC voltage Vout at the detection point C on the secondary side.
And the differential amplifier 28 controls the photocoupler 29 according to the voltage difference between the DC voltage at the voltage dividing point D obtained by the resistors R5 and R6 and the reference voltage source 27. For example, when the load is light and the DC voltage at the detection point C increases, the output level of the differential amplifier 28 increases because the voltage difference from the reference voltage is large.

Therefore, the transistor Q6 of the photocoupler 29 is in a low impedance state, a large current flows from the collector of the transistor Q2 of the mirror circuit 43 via the transistor Q6, and a large current proportional to this large current is supplied to the transistor of the mirror circuit 43. Q3 flows to the resistor Ra. That is, the current signal corresponding to the current at the time of light load is fed to the resistor Ra as feedback.

At this time, the current I3 flowing during the ON period of the switching element Q1 flows through the resistor R1 and the voltage signal V
4 is converted again by the buffer amplifier circuit 45 into a current corresponding to the current I3 flowing through the switching element Q1, and is passed through the resistor Ra.

That is, the DC pulse signal (current I) flowing through the connection point F between the switching element Q1 and the resistor R1 is provided by the mirror circuit 43, the buffer amplifier 45, and the resistor Ra.
3 is added to the secondary side DC voltage Vout.
Is added to the input terminal on the plus side of the comparator 50 of the control signal forming circuit 46.

Therefore, at the time of light load, the voltage generated at one end of the resistor Ra becomes higher than that at the time of heavy load, and the voltage I3 flowing through the switching element Q1 is added to this voltage.
Is added, a plus voltage signal V3 higher than the ground level is obtained at the positive input terminal of the comparator 50 of the control signal forming circuit 46 as shown in FIG. Become.

Next, the comparator 50 compares the added voltage signal V3 with the triangular wave signal V1, and when the voltage of the added voltage signal V3 becomes higher than the voltage of the triangular wave signal V1 as shown in FIG. Output signal V5 of the flip-flop 24
Is output to the reset terminal R.

Next, the NOR circuit 25 sends the output obtained by inverting the logical sum of the output signal of the flip-flop 24 and the triangular wave synchronizing pulse signal V2 to the drive circuit 26. When the output signal from the NOR circuit 25 is input, the drive circuit 26
As shown in FIG. 3, the drive signal V6 is set to the H level while the voltage of the added voltage signal V3 reaches the voltage of the triangular wave signal V1 from the highest peak of the triangular wave signal V1 (the output signal V5 is generated). And the current I3 flows through the switching element Q1.

At this time, the duty ratio of the drive signal V6 is 50% or less as shown in FIG.

That is, when the highest peak voltage of the added voltage signal V3 reaches the voltage of the falling waveform of the triangular wave signal V1, an H level output signal V5 is generated and the triangular wave signal V
A drive signal V6 having a duty ratio in which the rising peak of 1 is synchronized with the falling of the triangular wave synchronization pulse signal V2 and the H level is maintained until an output signal is generated.

That is, when the load is light, the phototransistor Q6 is turned on (low impedance state), the mirror circuit is operated, and the current signal flowing through the resistor Ra (the detection voltage of the DC voltage on the secondary side is obtained as a feedback signal. Current) is increased to increase the DC voltage of the added voltage signal V3.
Therefore, the noise margin with respect to the ground is increased by increasing the voltage per minute.

As a result, since the peak voltage of the added voltage signal V3 reaches the voltage of the triangular wave signal V1 earlier, the peak value of the current I3 flowing through the switching element Q1 decreases, and the loss of the resistor R1 can be suppressed.

Therefore, even in the switching power supply of the current mode type shown in FIG. 1, the duty ratio is 50% or less even in the continuous mode operation state at the time of light load, so that no subharmonic is generated. The DC voltage on the secondary side stabilizes.

(During heavy load) At the time of heavy load, the DC voltage Vout on the secondary side becomes lower than at the time of light load, so that the photocoupler 29 of the detection circuit section 18 enters a high impedance state. For this reason, Q2 and Q3 of the mirror circuit 43 are in a state close to off, and the voltage V3 generated at one end of the resistor Ra is a very low voltage as compared with a light load. Accordingly, the voltage V4 corresponding to the current I3 flowing through the switching element Q1 is added to this low voltage, so that the positive input terminal of the comparator 50 of the control signal forming circuit 46 is connected to the ground level as shown in FIG. As a result, an addition voltage signal V3 of a low voltage of about 1 V to 2.5 V is obtained,
3 arrives at the triangular wave signal V1 later.

Next, the added voltage signal V3 and the triangular wave signal V1 are compared by the comparator 50. When the voltage of the added voltage signal V3 reaches the voltage of the triangular wave signal V1 as shown in FIG. The output signal V5 is supplied to the flip-flop 24.
Is output to the reset terminal R.

Next, the NOR circuit 25 sends the output obtained by inverting the logical sum of the output signal of the flip-flop 24 and the triangular wave synchronizing pulse signal V2 to the drive circuit 26. When the output signal from the NOR circuit 25 is input, the drive circuit 26
As shown in FIG. 4, a drive signal V6 having an H level while the voltage of the added voltage signal V3 reaches the voltage of the triangular wave signal V1 from the highest peak of the triangular wave signal V1 (output signal V5) is applied to the gate of the switching element Q1. The current I3 is sent to the switching element Q1.

That is, at the time of heavy load, the impedance of the phototransistor Q6 is turned off (high impedance state) so that a DC current corresponding to the detection voltage of the secondary-side DC voltage is prevented from flowing from the mirror circuit 43 to the resistor Ra. To lower the DC voltage of the added voltage signal V3, so that the peak voltage of the added voltage signal V3 does not reach the voltage of the triangular wave signal V1 at a later time.
Is increased so that the peak value of the current I3 flowing through the current I3 increases.
For this reason, when the load becomes heavy, large power can be immediately obtained on the secondary side, so that the DC voltage on the secondary side is stabilized.

Therefore, the switching power supply of the first embodiment operates the mirror circuit 43 when the load is light, and detects the secondary-side DC voltage and the voltage at the connection point between the resistor R1 and the switching element Q1. The peak value of the current I3 flowing through the switching element Q1 is reduced by increasing the DC voltage of the added voltage signal V3 obtained by adding
With the mirror circuit 43 turned off, the added voltage waveform signal V3
, The peak voltage of the addition voltage signal V3 is delayed from reaching the voltage of the triangular wave signal V1, and the peak value of the current I3 flowing through the switching element Q1 is increased. This means that the output on the secondary side is set to a constant voltage.

<Second Embodiment> In the first embodiment, the triangular wave signal V1 from the triangular wave generating circuit 41 has the waveforms shown in FIGS. 3 and 4. In some cases, the triangular wave signal V1 is inverted to generate a triangular wave signal V1a and a triangular wave synchronizing pulse signal V2a (obtained by omitting the NOT circuit 44 in FIG. 2) as shown in FIG.

In such a case, the control signal forming circuit 4
6 at the input terminal on the plus side, the added voltage waveform signal V3
It is preferable to control the on / off of the switching element Q1 by obtaining a sum voltage waveform signal V3 obtained by inverting the switching element Q1 by, for example, a NOT circuit (not shown), and comparing it with the above-described triangular wave synchronization inversion signal V2.

The operation of the second embodiment will be described with reference to FIG. FIG. 5 shows an operation under heavy load.

The comparator 50 of the control signal forming circuit compares the added voltage waveform signal V3a with the triangular wave signal V1a, and
When the voltage of the added voltage waveform signal V3a falls below (attains) the voltage of the triangular wave signal V1a, the output signal V5 at H level is reset to the reset terminal R of the flip-flop 24 as shown in FIG.
Output to That is, the ON width control is performed as compared with the rising slope portion of the triangular waveform.

Next, the NOR circuit 25 sends the output obtained by inverting the logical sum of the output signal of the flip-flop 24 and the triangular wave synchronizing pulse signal V2a to the drive circuit 25. When the output signal from the NOR circuit 25 is input to the drive circuit 26, as shown in FIG. 5, the voltage of the added voltage signal V3a reaches the voltage of the triangular wave signal V1a or lower from the highest peak of the triangular wave signal V3a (V5 is output). ), The drive signal V6 at the H level is sent to the gate of the switching element Q1 to cause the current I3 to flow through the switching element Q1.

That is, an inverted addition voltage signal V3a is generated by inverting the addition voltage signal V3. When the lowest peak of the inverted addition voltage signal V3a reaches the voltage of the rising waveform of the triangular wave signal V1a, the output signal V5 is generated. Then, a drive signal V6 having a duty ratio in which the falling peak of the triangular wave signal V1a and the falling of the triangular wave synchronizing pulse signal V2a are at H level until the output signal V5 is generated is generated. .

For this reason, the triangular wave generating circuit is shown in FIGS.
Even if the triangular wave signal V1a and the triangular wave synchronizing pulse signal V2a shown in FIG. 5 are generated by inverting the triangular wave signal V1 shown in FIG. 5, large power can be immediately obtained on the secondary side when the load becomes heavy. The DC voltage on the secondary side is stabilized.

In the above embodiment, the DC voltage on the secondary winding side is detected using a photocoupler.
It may be performed on the primary winding and the auxiliary winding.

The switching element Q1 is a MOS F
A bipolar transistor or IGBT may be used instead of ET.

Further, the current of the switching element Q1 may be detected by using a sense MOS FET or the like to detect the shunted current flowing out of the sensing terminal.

Further, the buffer amplifier includes a capacitor C
And a circuit configuration of a low-pass filter using a resistor R.

[0107]

As described above, according to the present invention, a signal representing an error between a detection current when a current flowing through a switching element connected to a primary side of a transformer and an output voltage on a secondary side of the transformer is detected. The mirror current corresponding to the current flows through the resistance of the adder circuit. As a result, the detection current and the mirror current flow through the resistor, and an added voltage signal corresponding to the added current is obtained. Then, the control signal forming circuit turns on the switching element in synchronization with the rising or falling of the triangular wave signal, and compares the added voltage signal obtained from the adding circuit with the triangular wave signal obtained from the triangular wave generating circuit, The control signal forming circuit generates a control signal that turns off the switching element in synchronization with the output of the comparator that outputs an output signal when the added voltage signal reaches the triangular wave signal. While arriving,
A control signal having a duty ratio in the ON period of the switching element is generated in the switching element.

Therefore, at a light load, the added voltage is compared with the triangular wave reference voltage and the ground at a high level, so that the operation is less affected by noise and operates stably.

In addition, at the time of heavy load, the level of the added voltage signal becomes low, so that the arrival at the triangular wave signal is delayed. For this reason, even if noise occurs, it takes time to reach the triangular wave signal. As a result, a large current flows through the switching element, so that a stable output can be obtained on the secondary side. That is, even under the condition where the sub-harmonic phenomenon occurs, a circuit for countermeasures against the sub-harmonic phenomenon is not required, so that the circuit configuration can be simplified and stable operation can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a switching power supply device according to a first embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of a control circuit unit and a detection circuit unit according to the embodiment of the present invention.

FIG. 3 is a timing chart illustrating an operation under a light load when the control circuit unit of the present invention is used.

FIG. 4 is a timing chart illustrating an operation under heavy load when the control circuit unit of the present invention is used.

FIG. 5 is a timing chart illustrating the operation of the second embodiment.

FIG. 6 is a schematic configuration diagram of a conventional switching power supply of a voltage mode control method.

FIG. 7 is a detailed configuration diagram of a control circuit unit of a conventional switching power supply of a voltage mode control method.

FIG. 8 is a timing chart illustrating the operation of a conventional voltage mode control method.

FIG. 9 is a schematic configuration diagram of a conventional switching power supply device of a current mode control method.

FIG. 10 is a detailed configuration diagram of a control circuit unit of a conventional switching power supply of a current mode control method.

FIG. 11 is a timing chart illustrating an operation of a conventional current mode control method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 3 rectifying and smoothing circuit section 4 transformer 5 primary winding 10 secondary winding 18 detection circuit section 40 control circuit section 41 triangular wave oscillation circuit 42 addition circuit 43 mirror circuit 45 buffer amplifier Q1 switching element

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/335

Claims (6)

(57) [Claims] 1. A series circuit of a primary winding of a transformer and a switching element connected between one end and the other end of a DC power supply; a rectifier circuit connected to a secondary winding of the transformer; An output smoothing circuit connected to a circuit; a current detection circuit for detecting a current flowing through the switching element; and an output voltage for controlling a signal current according to an error between an output voltage of the output smoothing circuit and a reference voltage. A detection circuit, an addition circuit for adding a mirror current of the signal current and a detection current from the current detection circuit and flowing the resistance current through a resistor in accordance with the control, and a triangular wave generation for generating a triangular wave signal Circuit, the switching element is turned on in synchronization with the rising or falling of the triangular wave signal, the added voltage signal obtained from the adding circuit and the triangular wave generating circuit The control circuit compares the obtained triangular wave signal with the obtained triangular wave signal and generates a control signal that turns off the switching element in synchronization with an output of a comparator that outputs an output signal when the added voltage signal reaches the triangular wave signal. A switching power supply device comprising: a control signal forming circuit. 2. The addition circuit according to claim 1, wherein the addition circuit obtains the addition voltage signal by flowing a detection current from the current detection unit and the mirror current by a current mirror circuit through one resistor. A switching power supply as described. 3. The comparator, wherein the control signal forming circuit is configured to receive the added voltage signal obtained by the adding circuit on one side and to input a triangular wave signal from the triangular wave generating circuit to the other side for comparison, and the comparator A flip-flop in which an output signal from a triangular wave synchronizing pulse signal from the triangular wave generating circuit is input to a reset terminal, an output signal from the output terminal of the flip-flop, and the triangular wave synchronizing pulse signal. The switching power supply device according to claim 1, further comprising: a logic circuit that generates the control signal for driving an element. 4. The current detection circuit comprises: a current detection resistor for detecting a current flowing through the switching element; and an amplifier for converting a voltage generated between both ends of the current detection resistor into the detection current. The switching power supply according to claim 1, 2 or 3, wherein: 5. The triangular wave generating circuit has a triangular wave signal having a large rising slope and a gentle falling slope and a rising period from the lowest potential to the highest potential of the triangular wave signal as H.
5. The switching power supply device according to claim 1, wherein said switching power supply device outputs a triangular wave synchronization pulse signal having a level. 6. A triangular wave generating circuit, comprising: instead of the triangular wave signal and the triangular wave synchronizing pulse signal, a triangular wave signal obtained by inverting the triangular wave voltage and a triangular wave synchronizing inverted pulse signal obtained by inverting the triangular wave synchronizing pulse signal. 4. The method according to claim 1, wherein the transmission is performed.
6. The switching power supply according to 4 or 5.