JP2016189673A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit capable of suppressing an increase in a scale of the power supply circuit.SOLUTION: A power supply circuit comprises a switching element SW1 connected to a primary winding L1 of a transformer T1, a diode D connected to a secondary winding L2 of the transformer T1, and a control circuit 2 which generates a control signal S for controlling on and off of the switching element SW1. The control circuit generates a first pulse wave indicating an off timing of the switching element SW1 using the voltage Vt applied to the secondary winding L2 of the transformer T1 so that the difference between output voltage Vout and target voltage Vtar becomes zero. The control circuit also generates a control signal S using the first pulse wave transferred from a primary winding L1 of a pulse transformer T2 to a secondary winding L2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power supply circuit.

As the power supply circuit, for example, an insulating power supply circuit such as a flyback converter or a forward converter is known.
In addition, as a control method of the insulation type power supply circuit, for example, a pulse wave corresponding to the output voltage is fed back from the secondary side of the power supply circuit through the pulse transformer to the primary side, and the pulse wave is converted into an analog value. It is known to control the switching element connected to the primary winding of the transformer so that the difference between the analog value and the target voltage becomes zero. For example, see Patent Document 1.

JP 2011-130571 A

  However, the power supply circuit that performs the feedback control as described above has a circuit that generates a pulse wave corresponding to the output voltage, a circuit that converts the pulse wave into an analog value, and a difference between the analog value and the target voltage is zero. Since it is necessary to provide a circuit for controlling the switching element, the circuit scale increases.

  An object of one aspect of the present invention is to provide a power supply circuit in which an increase in circuit scale is suppressed.

  A power supply circuit according to one aspect of the present invention includes a transformer, a switching element connected to a primary winding of the transformer, a rectifier circuit connected to a secondary winding of the transformer, and an on-state of the switching element. And a control circuit for controlling OFF.

  The control circuit uses the voltage applied to the secondary winding to generate a first pulse wave indicating the control timing of the switching element so that the difference between the output voltage of the power supply circuit and the target voltage becomes zero. Generates a rectangular wave generation circuit to generate, a pulse transformer, and a control signal for controlling on / off of the switching element using the first pulse wave transmitted from the primary winding to the secondary winding of the pulse transformer And a control signal generation circuit.

  According to the present invention, an increase in circuit scale of the power supply circuit can be suppressed.

It is a figure which shows an example of the power supply circuit of embodiment. It is a figure which shows an example of an output waveform. It is a figure which shows an example of the power supply circuit of embodiment.

Hereinafter, embodiments will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a power supply circuit according to the embodiment.
The power supply circuit shown in FIG. 1 includes an insulated DCDC converter 1 and a control circuit 2.

  The isolated DCDC converter 1 is a flyback converter, and a voltage Vt applied to a transformer T1, a switching element SW1 (for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor)), and a secondary winding L2 of the transformer T1. A diode D (rectifier circuit) for rectification and a capacitor C1 for smoothing a voltage rectified by the diode D are provided. That is, one end of the primary winding L1 of the transformer T1 is connected to the output terminal of the external DC power supply P via the input terminal IN of the isolated DCDC converter 1, and the other end of the primary winding L1 of the transformer T1 is a switching element. Connected to one terminal (for example, drain terminal) of SW1, one end of secondary winding L2 of transformer T1 is connected to the anode terminal of diode D, and the other end of secondary winding L2 of transformer T1 is capacitor C1. Is connected to one of the terminals. The cathode terminal of the diode D is connected to the external load Lo via the other terminal of the capacitor C1 and the output terminal OUT of the insulated DCDC converter 1. The load Lo is, for example, a driving power source for a power switching element that constitutes each arm of a three-phase AC inverter that controls the motor. The other terminal (for example, the source terminal) of the switching element SW1 is connected to the first ground, and the other end of the secondary winding L2 of the transformer T1 and one terminal of the capacitor C1 are different from the first ground. Connected to ground.

  When the switching element SW1 is turned on, a current flows from the DC power source P to the switching element SW1 via the input terminal IN and the primary winding L1 of the transformer T1, and energy is stored in the transformer T1. Thereafter, when the switching element SW1 is turned off, a current flows from the secondary winding L2 of the transformer T1 to the load Lo via the diode D and the output terminal OUT due to the release of the energy accumulated in the transformer T1.

The control circuit 2 includes a pulse wave generation circuit 21, a pulse transformer T2, and a control signal generation circuit 22.
The pulse wave generation circuit 21 includes comparators Comp1 and Comp2, constant voltage sources Pcv1 and Pcv2, an error amplifier Amp, a constant current source Pcc, a switching element SW2 (for example, a MOSFET), and a capacitor C2. The positive input terminal of the comparator Comp1 is connected to one end of the secondary winding L2 of the transformer T1, the negative input terminal of the comparator Comp1 is connected to the output terminal of the constant voltage source Pcv1, and the output terminal of the comparator Comp1 is a switching element. It is connected to the control terminal (for example, gate terminal) of SW2. One terminal (for example, drain terminal) of the switching element SW2 is connected to the output terminal of the constant current source Pcc, one terminal of the capacitor C2, and the positive input terminal of the comparator Comp2. The other terminal (for example, the source terminal) of the switching element SW2 and the other terminal of the capacitor C2 are connected to the second ground. The negative input terminal of the error amplifier Amp is connected to the other terminal of the capacitor C1 or the output terminal OUT, the positive input terminal of the error amplifier Amp is connected to the output terminal of the constant voltage source Pcv2, and the output terminal of the error amplifier Amp is It is connected to the negative input terminal of the comparator Comp2. The output terminal of the comparator Comp2 is connected to one end of the primary winding L1 of the pulse transformer T2, and the other end of the primary winding L1 of the pulse transformer T2 is connected to the second ground.

  The control signal generation circuit 22 includes a clock generation circuit 221, an RS flip-flop 222, and a drive circuit 223. The reset terminal R of the RS flip-flop 222 is connected to one end of the secondary winding L2 of the pulse transformer T2, the set terminal S of the RS flip-flop 222 is connected to the output terminal of the clock generation circuit 221, and the RS flip-flop 222 The output terminal Q is connected to the input terminal of the drive circuit 223. An output terminal of the drive circuit 223 is connected to a control terminal (for example, a gate terminal) of the switching element SW1. The other end of the secondary winding L2 of the pulse transformer T2 is connected to a predetermined power source.

<Operation Example of Pulse Wave Generation Circuit 21>
First, the switching element SW1 is switched from OFF to ON, and the voltage Vt (voltage Vt applied to the secondary winding L2 of the transformer T1) input to the positive input terminal of the comparator Comp1 is input to the negative input terminal of the comparator Comp1. Lower than the threshold voltage Vth (threshold voltage Vth output from the constant voltage source Pcv1), the voltage output from the output terminal of the comparator Comp1 to the control terminal of the switching element SW2 changes from the high level to the low level. Then, the switching element SW2 is switched from on to off, charging of the capacitor C2 is started by the output current of the constant current source Pcc, and the voltage Vc (voltage Vc applied to the capacitor C2) input to the positive input terminal of the comparator Comp2 It begins to rise (time t1 in FIG. 2 (a)).

  Next, when the voltage Vc input to the positive input terminal of the comparator Comp2 becomes larger than the voltage Ve input to the negative input terminal of the comparator Comp2, the primary winding L1 of the pulse transformer T2 and the output terminal of the comparator Comp2 The voltage Vr output to the reset terminal R of the RS flip-flop 222 through the secondary winding L2 changes from low level to high level (time t2 in FIG. 2A).

  When the switching element SW1 is switched from on to off and the voltage Vt input to the positive input terminal of the comparator Comp1 becomes larger than the threshold voltage Vth input to the negative input terminal of the comparator Comp1, the output terminal of the comparator Comp1. Is output from the low level to the high level. Then, the switching element SW2 is switched from OFF to ON, the capacitor C2 is discharged, and the voltage Vc input to the positive input terminal of the comparator Comp2 becomes smaller than the voltage Ve input to the negative input terminal of the comparator Comp2. The voltage Vr output from the output terminal of the comparator Comp2 to the reset terminal R of the RS flip-flop 222 through the primary winding L1 and the secondary winding L2 of the pulse transformer T2 changes from high level to low level (FIG. 2 (a ) Time t3). That is, the circuit composed of the comparator Comp1, the constant voltage source Pcv1, the switching element SW2, the constant current source Pcc, and the capacitor C2 generates a “sawtooth wave” that is substantially synchronized with the control signal S generated on the primary side of the power supply circuit. On the secondary side of The comparator Comp2 resets the RS flip-flop 222 via the pulse transformer T2 with the voltage Vr (first pulse wave indicating the control timing) having a pulse width corresponding to the comparison result between the “saw wave” and the voltage Ve. Output to terminal R. Thereby, the first pulse wave (rectangular wave) substantially synchronized with the control signal S can be fed back from the secondary side of the power supply circuit to the primary side.

<Operation Example of Control Signal Generation Circuit 22>
First, when the voltage Vs output from the output terminal of the clock generation circuit 221 to the set terminal S of the RS flip-flop 222 changes from the low level to the high level, the voltage output from the output terminal Q of the RS flip-flop 222 to the drive circuit 223. Vo changes from the low level to the high level, the control signal S output from the drive circuit 223 to the control terminal of the switching element SW1 changes from the low level to the high level, and the switching element SW1 switches from OFF to ON (FIG. 2B). ) Time t1). It is assumed that the voltage Vs changes from the low level to the high level at a constant cycle, and changes from the high level to the low level after a lapse of a fixed time after changing from the low level to the high level. That is, the voltage Vs corresponds to “a second pulse wave (rectangular wave) indicating the ON timing of the switching element SW1”.

  Next, when the voltage Vr output from the output terminal of the comparator Comp2 through the primary winding L1 and the secondary winding L2 of the pulse transformer T2 to the reset terminal R of the RS flip-flop 222 is changed from low level to high level, RS The voltage Vo output from the output terminal Q of the flip-flop 222 to the drive circuit 223 changes from high level to low level, and the control signal S output from the drive circuit 223 to the control terminal of the switching element SW1 changes from high level to low level. Thus, the switching element SW1 is switched from on to off (time t2 in FIG. 2B).

<Example of feedback control when output voltage Vout is higher than target voltage Vtar>
As the output voltage Vout becomes higher than the target voltage Vtar, the voltage Ve output from the output terminal of the error amplifier Amp to the negative input terminal of the comparator Comp2 decreases. As the voltage Ve decreases, the timing at which the voltage Vr switches from the low level to the high level (the time t2 in FIG. 2A and the time t2 in FIG. 2B) is earlier, so the off timing of the switching element SW1 is also earlier. . Further, since the voltage Vs changes from the low level to the high level at a constant cycle, the on-timing of the switching element SW1 does not change. Therefore, as the output voltage Vout becomes larger than the target voltage Vtar, the ON period of the switching element SW1 is shortened, and the output voltage Vout is reduced accordingly, so that the output voltage Vout approaches the target voltage Vtar.

<Example of feedback control when the output voltage Vout is smaller than the target voltage Vtar>
As the output voltage Vout becomes lower than the target voltage Vtar, the voltage Ve output from the output terminal of the error amplifier Amp to the negative input terminal of the comparator Comp2 increases. As the voltage Ve increases, the timing at which the voltage Vr switches from the low level to the high level (the time t2 in FIG. 2A and the time t2 in FIG. 2B) is delayed, so the off timing of the switching element SW1 is also delayed. . Further, since the voltage Vs changes from the low level to the high level at a constant cycle, the on-timing of the switching element SW1 does not change. Therefore, as the output voltage Vout becomes lower than the target voltage Vtar, the ON period of the switching element SW1 becomes longer, and the output voltage Vout increases accordingly, so that the output voltage Vout approaches the target voltage Vtar.

  That is, the pulse wave generation circuit 21 uses the voltage Vt applied to the secondary winding L2 of the transformer T1 to generate the output voltage Vout (output voltage of the power supply circuit) applied to the capacitor C1 or the output terminal OUT and the target voltage Vtar. A first pulse wave indicating the control timing (off timing) of the switching element SW1 is generated so that the difference becomes zero. Further, the control signal generation circuit 22 turns on and off the switching element SW1 using the first pulse wave and the second pulse wave transmitted from the primary winding L1 to the secondary winding L2 of the pulse transformer T2. A control signal S to be controlled is generated.

  The circuit configuration of the pulse wave generation circuit 21 is a circuit configuration that can generate the first pulse wave by using the voltage Vt so that the difference between the output voltage Vout and the target voltage Vtar becomes zero. If there is, it is not limited to the circuit configuration shown in FIG. The circuit configuration of the control signal generation circuit 22 is a circuit configuration that can generate the control signal S using the first pulse wave transmitted from the primary winding L1 to the secondary winding L2 of the pulse transformer T2. If there is, it is not limited to the circuit configuration shown in FIG.

  As described above, the power supply circuit according to the embodiment includes the pulse wave generation circuit 21 and the control signal generation circuit 22 to configure the control circuit 2. Thereby, a circuit for generating a pulse wave corresponding to the output voltage Vout, a circuit for converting a pulse wave transmitted from the primary winding to the secondary winding of the pulse transformer T2 into an analog value, and a difference between the analog value and the target voltage Vtar The circuit scale of the control circuit 2 can be reduced as compared with a control circuit including a circuit that generates the control signal S of the switching element SW1 so that becomes zero. Therefore, an increase in circuit scale of the power supply circuit can be suppressed.

The present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the gist of the present invention.
In the above embodiment, a flyback converter is adopted as the isolated DCDC converter 1, but a forward converter further including a diode D2 (rectifier circuit) and an inductor L as shown in FIG. May be adopted.

  In the above embodiment, the off timing of the switching element SW1 is transmitted to the primary winding L1 of the pulse transformer T2. However, the on timing may be transmitted as the first pulse wave indicating the control timing. In this case, the clock generation circuit 221 can generate an off timing and control the on time of the switching element SW1 by advancing or delaying the on timing.

DESCRIPTION OF SYMBOLS 1 DCDC converter 2 Control circuit 21 Pulse wave generation circuit 22 Control signal generation circuit 221 Clock generation circuit 222 Flip-flop 223 Drive circuit

Claims (3)

With a transformer,
A switching element connected to the primary winding of the transformer;
A rectifier circuit connected to the secondary winding of the transformer;
A control circuit for generating a control signal for controlling on and off of the switching element;
With
The control circuit includes:
Pulse wave generation using the voltage applied to the secondary winding to generate a first pulse wave indicating the control timing of the switching element so that the difference between the output voltage of the power supply circuit and the target voltage becomes zero Circuit,
A pulse transformer,
A control signal generation circuit for generating the control signal using the first pulse wave transmitted from the primary winding of the pulse transformer to the secondary winding;
A power supply circuit comprising: The power supply circuit according to claim 1,
The control timing is an off timing of the switching element,
The power supply circuit, wherein the control signal generation circuit generates the control signal by using the first pulse wave and a second pulse wave indicating an on timing of the switching element. The power supply circuit according to claim 2,
The pulse wave generation circuit switches from a low level to a high level earlier as the output voltage becomes higher than the target voltage, and switches from a low level to a high level as the output voltage becomes lower than the target voltage. Generating the first pulse wave that is delayed in timing;
When the level of the second pulse wave is changed from a low level to a high level, the control signal generation circuit switches the level of the control signal from a low level to a high level, and the level of the first pulse wave is changed from a low level. A power supply circuit that switches the level of the control signal from a high level to a low level when the level is high.

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