JP5034393B2 - Switching regulator - Google Patents

Description

  The present invention relates to a switching regulator that boosts or lowers an input voltage by turning on and off a switching element.

Some general switching regulators maintain the output voltage at the target voltage by adjusting the gain and phase of PI control based on the fed back output voltage and the target voltage.
However, in the switching regulator having such a configuration, there is a possibility that the output voltage exceeds the target voltage at the start-up due to a signal delay existing in the feedback system circuit. In addition, when the output voltage exceeds the target voltage at the start-up (overshoot) is large, it is necessary to increase the breakdown voltage of the parts used in accordance with the overshoot, which is disadvantageous in terms of physique and cost. is there.

Therefore, conventionally, there is a method of improving the responsiveness and adjusting the overshoot by adjusting the gain and phase of PI control of the feedback system.
However, when the feedback system is configured with an analog circuit, the gain and phase of PI control become the same value even after startup, so that the output voltage after startup may become unstable and worst oscillation may occur. .

Therefore, conventionally, the switching regulator has a function of gradually increasing the duty of the control signal input to the switching element until the output voltage reaches the target voltage after the switching regulator is activated. In some cases, the duty of the control signal of the switching element is reduced to suppress overshooting until the output voltage reaches the target voltage. (For example, see Patent Document 1)
FIG. 3 is a diagram showing an existing switching regulator having a soft start function.

  The switching regulator 30 shown in FIG. 3 outputs a voltage conversion circuit 31 that boosts the input voltage Vin to the output voltage Vout, and a voltage Vdtc that gradually increases with the reference voltage VREF input when the switching regulator 30 is activated. The output circuit 32 includes a control circuit 33 that controls the operation of the voltage conversion circuit 31 based on the output voltage Vout and the voltage Vdtc.

  The voltage conversion circuit 31 includes a coil 34, a switching element (npn bipolar transistor in the example shown in FIG. 3) 35, a diode 36, and a capacitor 37. That is, one end of the coil 34 is connected to the high side of the input voltage Vin, and the other end of the coil 34 is connected to the collector terminal of the switching element 35 and the anode terminal of the diode 36. The emitter terminal of the switching element 35 is connected to the ground. One end of the capacitor 37 is connected to the cathode of the diode 36, and the other end of the capacitor 37 is connected to the ground. The voltage applied to the capacitor 37 becomes the output voltage Vout.

  The voltage output circuit 32 includes a resistor 38 having one end connected to the high side of the reference voltage VREF, and a capacitor 39 having one end connected to the other end of the resistor 38 and the other end connected to the ground. Configured. A voltage Vdtc between the resistor 38 and the capacitor 39 is input to the control circuit 33. When the switching regulator 30 is activated, charging of the capacitor 39 is started and the voltage Vdtc gradually increases.

  The control circuit 33 outputs a control signal Sc to the base terminal of the switching element 35 to turn the switching element 35 on and off, so that the energy accumulated in the coil 34 is discharged to the capacitor 37 via the diode 36. Yes. The output voltage Vout applied to the capacitor 37 is controlled by the duty of the control signal Sc, and the duty of the control signal Sc is controlled based on the output voltage Vout and the output voltage Vdtc.

FIG. 4 is a diagram illustrating a timing chart of each signal generated inside the control circuit 33 when the control signal Sc is generated.
As shown in FIG. 4, inside the control circuit 33, a triangular wave St is generated by a triangular wave generation unit (not shown).

  In the control circuit 33, a pulse signal S1 corresponding to the comparison result between the input voltage Vdtc and the triangular wave St is generated by a first pulse signal generator (not shown). In the example shown in FIG. 4, the pulse signal S1 is at a high level when the voltage Vdtc is larger than the triangular wave St, and is at a low level when the voltage Vdtc is smaller than the triangular wave St.

Further, inside the control circuit 33, a difference Vd between the input output voltage Vout and the target voltage Vt is calculated by a difference calculation unit (not shown).
In the control circuit 33, a pulse signal S2 corresponding to the comparison result between the difference Vd and the triangular wave St is generated by a second pulse signal generation unit (not shown). That is, in the example shown in FIG. 4, the pulse signal S2 is at a high level when the difference Vd is larger than the triangular wave St, and is at a low level when the difference Vd is smaller than the triangular wave St.

In the control circuit 33, an AND operation unit (not shown) performs an AND operation on the pulse signal S1 and the pulse signal S2, and the operation result is output as the control signal Sc.
Thereby, as shown in FIG. 4, the switching regulator 30 gradually increases the duty of the control signal Sc until the output voltage Vout becomes the target voltage Vt after the switching regulator 30 is activated. And overshoot can be suppressed.
JP 2004-180463 A

  However, since the switching regulator 30 delays the output voltage Vout in the control circuit 33 as described above, the difference Vd calculated in the control circuit 33 (solid line difference Vd shown in FIG. 4) is obtained. There is a delay from the difference Vd between the actual output voltage Vout and the target voltage Vt (broken line difference Vd shown in FIG. 4). For this reason, even when the output voltage Vout reaches the target voltage Vt, the duty of the control signal Sc does not become zero, and there is a possibility that overshoot may occur.

  Therefore, an object of the present invention is to provide a switching regulator that can suppress overshoot even if it has a soft start function.

In order to solve the above problems, the present invention adopts the following configuration.
That is, the switching regulator of the present invention includes a switching element that is turned on / off based on an input control signal, a voltage conversion circuit that steps up or down an input voltage by turning on / off the switching element, and the switching regulator. A voltage output circuit that outputs a voltage that gradually increases or decreases when the oscillator is started, and a first pulse signal that gradually increases in duty as the voltage output from the voltage output circuit increases or decreases. , Generating a second pulse signal whose duty gradually decreases as the difference between the output voltage of the voltage conversion circuit and the target voltage approaches zero, and ANDing the first pulse signal and the second pulse signal A control circuit for outputting a result of the operation as a control signal for the switching element, and the switching leg And a reset circuit for returning the voltage output from the voltage output circuit to the original voltage before rising or falling when the output voltage of the voltage conversion circuit has not reached the target voltage .

  As a result, the switching regulator of the present invention simply resets the soft start function when the output voltage of the voltage conversion circuit does not reach the target voltage. Compared to the switching regulator, the duty of the control signal when the output voltage of the switching regulator approaches the target voltage can be further reduced, and the overshoot that occurs even with the soft start function can be suppressed.

  The reset circuit is configured to determine that the output voltage of the voltage conversion circuit has reached the predetermined voltage by determining that the output voltage of the voltage conversion circuit has reached a voltage lower than the predetermined voltage. May be.

  Further, the reset circuit may be configured to determine that the output voltage of the voltage conversion circuit has reached the predetermined voltage by determining that a preset time has been reached since the activation of the switching regulator. .

  According to the present invention, overshoot can be suppressed in a switching regulator having a soft start function.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a switching regulator according to an embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same structure as the structure shown in FIG.

  The switching regulator 1 shown in FIG. 1 includes a voltage conversion circuit 31, a voltage output circuit 32, a control circuit 33, and a reset circuit 2. The voltage conversion circuit 31 is a step-up converter, but may be configured as a step-down converter. The voltage conversion circuit 31 may be configured as an insulating push-pull converter using a transformer.

  The reset circuit 2 includes a switch 3 connected in parallel to a capacitor 39, and a switch control circuit 4 that outputs a reset control signal Sr to the switch 3 to control on / off of the switch 3.

  The switch control circuit 4 outputs a reset control signal Sr that turns on the switch 3 for a certain period when the output voltage Vout has not reached the target voltage Vt after the switching regulator 1 is activated. The term “not reached” includes “below (<)” and “below (≦)”.

  For example, the switch control circuit 4 outputs a reset control signal Sr that turns on the switch 3 for a certain period when the output voltage Vout becomes a predetermined voltage V1 that is equal to or lower than the target voltage Vt after the switching regulator 1 is activated. The switch control circuit 4 outputs a reset control signal Sr for turning off the switch 3 when the output voltage Vout is not the predetermined voltage V1.

  The predetermined voltage V1 sufficiently suppresses the overshoot of the output voltage Vout in consideration of the capacitance of the capacitor 37, the time constant of the resistor 38 and the capacitor 39, the frequency of the triangular wave St, the input voltage Vin, the target voltage Vt, and the like. Is set to a possible value.

Further, it is assumed that the certain period is set to a time necessary for the switch 3 to be turned on and the electric charge accumulated in the capacitor 39 is sufficiently discharged.
In addition, the switch control circuit 4 includes, for example, a comparator that becomes a high level when the output voltage Vout reaches a voltage lower than the predetermined voltage V1, and excludes the output signal of the comparator and the delay signal of the output signal of the comparator. A logical OR may be output as the reset control signal Sr. The voltage lower than the predetermined voltage V1 is set, for example, so that the output voltage Vout and the predetermined voltage V1 are equal when the output voltage Vout reaches the voltage. The term “reached” includes “exceeding (>)” and “above (≧)”. The same applies to “reached” described later.

  The switch control circuit 4 determines that the output voltage Vout has reached the predetermined voltage V1 by determining that a preset time has elapsed since the activation of the switching regulator 1 using, for example, a timer. A short pulse reset control signal Sr may be output at the timing.

  FIG. 2 is a diagram showing a timing chart of each signal generated inside the control circuit 33 in the switching regulator 1 of the present embodiment. The operations of a triangular wave generation unit (not shown), a first pulse signal generation unit, a difference calculation unit, a second pulse signal generation unit, and an AND calculation unit provided in the control circuit 33 in the switching regulator 1 are illustrated in FIG. Since the operation is the same as that described in FIG.

  As shown in FIG. 2, the voltage Vdtc gradually rises when the switching regulator 1 is started, and returns to the voltage before the rise when the output voltage Vout becomes the predetermined voltage V1 (timing of the broken line A shown in FIG. 2). It gradually rises again. Therefore, the duty of the pulse signal S1 gradually increases after the switching regulator 1 is activated until the output voltage Vout reaches the predetermined voltage V1, becomes zero when the output voltage Vout reaches the predetermined voltage V1, and then gradually decreases again. It gets bigger. Thereby, the duty of the control signal Sc gradually increases when the switching regulator 1 is started, becomes zero when the output voltage Vout reaches the predetermined voltage V1, and then gradually increases again. That is, the switching regulator 1 of the present embodiment resets the soft start function when the output voltage Vout reaches the predetermined voltage V1. The term “gradually” includes the meaning of “continuously”, “stepwise”, or a combination thereof. The same applies to “gradually” described later.

  Therefore, as described above, the switching regulator 1 of the present embodiment further increases the duty of the control signal Sc when the output voltage Vout approaches the target voltage Vt, as compared with the switching regulator 30 that simply has the soft start function. It can be squeezed small, and overshoot can be suppressed. That is, in the switching regulator 1 of the present embodiment, the duty of the control signal Sc that causes overshoot is sufficiently reduced by resetting the soft start function. Can be suppressed. Thereby, the switching regulator 1 of this embodiment can be comprised, without using a high voltage | pressure-resistant expensive component.

  In the above embodiment, the pulse signal S1 is generated based on the comparison result between the voltage Vdtc that gradually increases after the switching regulator 1 is started up and the triangular wave St, but gradually after the switching regulator 1 is started up. The pulse signal S1 may be generated based on a comparison result between the decreasing voltage Vdtc and the inverted signal of the triangular wave St. In this case, it is necessary to change the configuration of the voltage output circuit 32 so that the voltage Vdtc gradually decreases after the switching regulator 1 is started. Further, when the output voltage Vout becomes the predetermined voltage V1, it is necessary to change the configuration of the reset circuit 2 so that the voltage Vdtc returns to the original voltage before dropping. Further, when generating the pulse signal S2, it is necessary to invert the difference Vd and the triangular wave St, respectively.

It is a figure which shows the switching regulator of embodiment of this invention. It is a figure which shows the timing chart of each signal generate | occur | produced inside the control circuit in the switching regulator of this embodiment. It is a figure which shows the existing switching regulator. It is a figure which shows the timing chart of each signal which generate | occur | produces inside the control circuit in the existing switching regulator.

Explanation of symbols

1 switching regulator 2 reset circuit 3 switch 4 switch control circuit 30 switching regulator 31 voltage conversion circuit 32 voltage output circuit 33 control circuit 34 coil 35 switching element 36 diode 37 capacitor 38 resistor 39 capacitor S1 pulse signal (first pulse signal) )
S2 Pulse signal (second pulse signal)

Claims (3)

A voltage conversion circuit that includes a switching element that is turned on and off based on an input control signal, and that steps up or down the input voltage by turning on and off the switching element;
A voltage output circuit that outputs a voltage that gradually increases or decreases when the switching regulator is activated;
A first pulse signal whose duty gradually increases as the voltage output from the voltage output circuit rises or falls is generated, and as the difference between the output voltage of the voltage conversion circuit and the target voltage approaches zero A control circuit that generates a second pulse signal with a gradually decreasing duty and outputs a result of an AND operation between the first pulse signal and the second pulse signal as a control signal of the switching element;
At any timing during which the output voltage of the voltage conversion circuit has not reached the target voltage after the switching regulator is activated, the voltage output from the voltage output circuit is changed to the original value before the rise or before the fall. A reset circuit to restore the voltage,
A switching regulator comprising: A switching regulator according to claim 1,
The reset circuit increases or decreases the voltage output from the voltage output circuit at a timing when the output voltage of the voltage conversion circuit reaches a predetermined voltage lower than the target voltage after the switching regulator is activated. Return to the previous voltage ,
A switching regulator characterized by that. A switching regulator according to claim 1,
Said reset circuit, at a timing when the switching the regulation regulator has reached a preset time after starting, back to the original voltage before rising front or lower the voltage output from the voltage output circuit,
A switching regulator characterized by that.

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