JP4487703B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply, and more particularly to a switching power supply that is switched to another power supply according to a load and supplies electric power.

  There is a power supply system that includes a plurality of power supply devices and switches the power supply devices according to a load. In such a power supply system, the power efficiency is improved by switching the power supply device according to the load weight.

  FIG. 12 is a block diagram of a conventional power supply system. As shown in the figure, the power supply system includes a power supply E101, a switch SW101, a switching power supply 101, a series power supply 102, and a capacitor C101. A load 103 is connected to the output.

  The switch SW101 is turned on when it is desired to supply maximum power to the load 103. Since the switching power supply 101 can obtain high power efficiency when the load current is relatively large, it is used when the load 103 requires a large current. The series power supply 102 is used when the load 103 is lightest. As described above, the operation of the switch SW101, the switching power supply 101, and the series power supply 102 is switched according to the state of the load 103 to improve the power efficiency. A plurality of switching power supplies and series power supplies can be provided, and the operation can be finely switched according to the load condition.

Some switching power supplies 101 and series power supplies 102 can adjust an output current according to a command voltage.
FIG. 13 is a circuit diagram showing an example of a conventional step-down switching power supply. As illustrated, the switching power supply includes resistors R101 to R103, capacitors C111 and C112, an operational amplifier OP101, a comparator COMP101, a driver 111, transistors M101 and M102, and a coil L101. Although there are other step-up and step-up / step-down switching power supplies, the operation principle is similar to that of the step-down type, and therefore the description will be made only for the step-down type of FIG.

In the switching power supply shown in the figure, the output voltage Vout output from the coil L101 is divided by resistors R101 and R102 and input to the inverting input terminal of the operational amplifier OP101. The operational amplifier OP101 constitutes an error amplifier and outputs the difference between the divided output voltage Vout and the command voltage Vref. A phase compensation feedback circuit including a resistor R103 and a capacitor C111 is connected between the output of the operational amplifier OP101 and the inverting input terminal. The comparator COMP101 receives the difference signal output from the operational amplifier OP101 and, for example, a triangular wave oscillation voltage Vosc, and compares the magnitudes thereof. The comparator COMP101 outputs the comparison result to the driver 111, and performs on / off control of the PMOS transistor M101 and the NMOS transistor M102 to which the voltage Vin from the power source is input as the source. As a result, the output voltage Vout corresponding to the command voltage Vref is output via the coil L101. The output voltage Vout is expressed by the following equation.
Vout = {1+ (R101 / R102)} × Vref (1)
In Equation (1), R101 and R102 are resistance values of the resistors R101 and R102, and Vref is a voltage value of the command voltage Vref.

FIG. 14 is a circuit diagram showing another example of a conventional step-down switching power supply. 14, the same components as those in FIG. 13 are denoted by the same reference numerals, and the description thereof is omitted. In the switching power supply shown in FIG. 14, the output voltage Vout is input to the inverting input terminal of the operational amplifier OP101 without being divided. The switching power supply of FIG. 14 can adjust the output voltage Vout by changing the command voltage Vref as in the switching power supply of FIG. The output voltage Vout in this case is represented by the following equation.
Vout = Vref (2)
When changing the output voltage by changing the above command voltage, switching between the switching power supply and another power supply, and starting / stopping the switching power supply, the output voltage changes suddenly. In response to this sudden change in output voltage, increasing the response speed of the switching power supply and setting the settling time to several microseconds to several hundred microseconds or less is restricted by the passive elements of the switching power supply shown in FIGS. Have difficulty.

In response to such a problem, when the output voltage of the switching power supply is changed to a low voltage, the response speed is slowed down by controlling the charge / discharge of the capacitor (corresponding to the capacitor C112 in FIGS. 13 and 14) of the output unit. There is a reduced power supply device (see, for example, Patent Document 1). In addition, the switching power supply changes and becomes unstable at the critical point between the continuous mode in which the current of the choke coil continuously flows and the discontinuous mode in which the current flows intermittently. Thus, there is a switching power supply device with improved stability (for example, see Patent Document 2).
JP 2003-333837 A (paragraph number [0033], FIG. 1) JP-A-5-304771 (paragraph number [0010], FIG. 1)

  However, the slowing of the response speed is also affected by the error amplifier. As shown in FIGS. 13 and 14, the error amplifier uses an operational amplifier and feeds back the output of the operational amplifier to the input. In some cases, a capacitor is inserted into the feedback section, and the response speed is slowed down due to charging and discharging of the capacitor.

  The present invention has been made in view of these points, and an object of the present invention is to provide a switching power supply that can quickly shift the output voltage to a set voltage when the output voltage is changed, started, or stopped. .

In the present invention, in order to solve the above problem, in a switching power supply that is switched to another power supply according to a load and supplies electric power, a command voltage for setting an output voltage to be output to the load and a response to the output voltage An error amplifier that outputs an error signal of a difference from the feedback voltage, a feedback circuit including a resistor and a capacitor connected between the output and the input of the error amplifier, and a switch that charges and discharges the charge of the capacitor , the switching element for supplying the electric power to the load connected in series between the supply voltage and ground, and a comparator for turning on / off alternately in response to a result of comparison between the error signal and the oscillation voltage, wherein A switch is inserted in series with the feedback circuit and is turned on when the switching power supply supplies power to the load, and is turned off when the other power supply supplies power to the load. Switching power supply is provided which is characterized in that.

According to such a switching power supply, is inserted in series in the feedback circuit, by a switch is turned on, is turned off when the other power supplies power to the load when the switching power supply supplies power to the load, the error amplifier The charge of the capacitor included in the feedback circuit is held and charged and discharged, and the settling time of the error signal output to the comparator is shortened.
Further, in the present invention, in order to solve the above problem, in a switching power supply that is switched to another power supply according to a load and supplies power, a command voltage for setting an output voltage to be output to the load, and the output voltage A feedback circuit including an error amplifier that outputs an error signal of a difference from a feedback voltage corresponding to the output voltage, a resistor and a capacitor connected between the output and the input of the error amplifier, and charging and discharging the capacitor A switch and a comparator that alternately turns on / off a switch element that supplies the power to the load that is connected in series between a power supply voltage and a ground according to a comparison result between the error signal and an oscillation voltage. The switch is inserted between the output of the error amplifier and the ground, and is turned on when the switching power supply is stopped, and is turned off when the switching power supply is in operation. Switching power supply is provided which is characterized in the that the.
According to such a switching power supply, it is inserted in the feedback circuit of the error amplifier by a switch that is inserted between the output of the error amplifier and the ground, is turned on when the switching power supply is stopped, and is turned off when the switching power supply is in operation. The charge of the capacitor is held and charged and discharged, and the settling time of the error signal output to the comparator is shortened.

The switching power supply of the present invention, is inserted in series in the feedback circuit, it is turned on when the switching power supply supplies power to a load, the switch is turned off when the other power supplies power to the load, feedback error amplifier The charge of the capacitor included in the circuit is held and charged / discharged to shorten the settling time of the error signal output to the comparator. As a result, the output voltage output to the load can be quickly transferred to the set voltage.
The switching power supply according to the present invention is included in the feedback circuit of the error amplifier by a switch that is inserted between the output of the error amplifier and the ground, is turned on when the switching power supply is stopped, and is turned off when the switching power supply is in operation. The charge of the capacitor is held and charged and discharged, and the settling time of the error signal output to the comparator is shortened. As a result, the output voltage output to the load can be quickly transferred to the set voltage.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. In the first embodiment, an improvement in responsiveness when the operation is switched from a plurality of power sources as shown in FIG. 12 to a switching power source and the operation is switched from the switching power source to another power source will be described.

  FIG. 1 is a circuit diagram of a switching power supply according to the first embodiment. As shown in the figure, the switching power supply includes resistors R1 to R3, an operational amplifier OP1, a comparator COMP1, capacitors C1 and C2, a switch SW1, a driver 11, transistors M1 and M2, and a coil L1. The switching power supply is connected to a capacitor C2 in parallel with a load. For example, as described with reference to FIG. 12, the switching power supply is switched to another power supply according to the load to supply power.

  The resistors R1 and R2 are connected in series, divide the output voltage Vout output from the coil L1, and output it to the inverting input terminal of the operational amplifier OP1. The output voltage Vout may be directly input to the inverting input terminal of the operational amplifier OP1 without being divided.

  The operational amplifier OP1 receives the output voltage Vout (voltage VA) divided by the resistors R1 and R2 at the inverting input terminal. The command voltage Vref is input to the non-inverting input terminal. The operational amplifier OP1 is an error amplifier, and outputs an error signal (voltage VB) of the difference between the voltage VA and the command voltage Vref to the comparator COMP1.

  A resistor R3, a capacitor C1, and a switch SW1 connected in series are connected between the output of the operational amplifier OP1 and the inverting input terminal. The resistor R3 and the capacitor C1 are a feedback circuit for phase compensation, and compensate so that the phase of the filter by the coil L1 and the capacitor C1 does not shift 180 degrees.

  The switch SW1 is turned on / off when the power source for supplying power to the load is switched as described with reference to FIG. By turning on / off the switch SW1, the feedback circuit is opened or closed to control the charge / discharge of the charge stored in the capacitor C1, and the charge / discharge time of the capacitor C1 when the power source is switched is reduced.

  The comparator COMP1 receives a voltage VB output from the operational amplifier OP1 and, for example, a triangular wave oscillation voltage Vosc. The comparator COMP1 compares the voltage VB with the oscillation voltage Vosc and outputs the comparison result to the driver 11.

The driver 11 increases the drive capability of the output of the comparator COMP1 so that the transistors M1 and M2 can be alternately turned on / off.
The transistor M1 is a PMOS transistor, and the transistor M2 is an NMOS transistor. The source of the transistor M1 is connected to the power supply, and the voltage Vin is input. The drains of the transistors M1 and M2 are connected to each other and to one end of the coil L1. The source of the transistor M2 is connected to the ground.

  The transistors M1 and M2 are alternately turned on / off according to the comparison result of the comparator COMP1. As a result, the voltage Vin is applied to the coil L1, one end of the coil L1 is connected to the ground, and the voltage Vin is intermittently applied to the coil L1.

  One end of the coil L1 is connected to the drains of the transistors M1 and M2. The other end is connected to the capacitor C2 and the resistor R1. One end of the capacitor C2 is connected to the ground. The coil L1 and the capacitor C2 constitute a filter, and smooth the intermittent voltage output from the transistors M1 and M2. As described above, the output voltage Vout corresponding to the command voltage Vref is output via the coil L1. When the command voltage Vref is constant, even if the load connected to the output fluctuates due to feedback of the output voltage Vout, the switching operation of the transistors M1 and M2 is controlled following the change. The illustrated switching power supply always operates to output a constant output voltage Vout.

Here, the oscillation voltage Vosc input to the comparator COMP101 in FIGS. 13 and 14 will be described.
FIG. 2 is a diagram illustrating the oscillation voltage input to the comparator. 13 and 14 is inputted with a triangular wave oscillation voltage of the maximum voltage Vosct and the minimum voltage Voscb as shown in the figure. The triangular wave oscillation voltage shown in FIG. 2 is also input to the comparator COMP1 of FIG.

In the switching power supply shown in FIGS. 13 and 14, the output voltage Vout is adjusted so that the command voltage Vref and the voltage VA are equal. In this case, the voltage VB output from the operational amplifier OP101 is within the amplitude of the triangular wave voltage, and Voscb = <VB = <Vosct. The voltage Cf across the capacitor C111 in FIGS. 13 and 14 is represented by the following equations, respectively.
Cf = VB− {R2 / (R1 + R2)} × Vout (3)
Cf = VB−Vout (4)
VB is a voltage value of the voltage VB output from the operational amplifier OP101, R1 and R2 are resistance values of the resistors R101 and R102, and Vout is a voltage value of the output voltage Vout. The capacitor C111 is charged with the voltage Cf shown in equations (3) and (4).

Next, the case where the power supply source is switched from the power supply E101 to the switching power supply 101 in the power supply system shown in FIG.
When the switch SW101 shown in FIG. 12 is turned on and power is directly supplied from the power supply E101, the transistor M101 of the switching power supply 101 (switching power supply shown in FIGS. 13 and 14) is turned on and the transistor M102 is turned off. The state of these transistors M101 and M102 can be achieved by adjusting the command voltage Vref so that the target output voltage of the switching power supply becomes higher than the voltage Vin of the power supply E101. In this case, since the output voltage Vout of the switching power supply is limited to the voltage Vin of the power supply E101 and cannot reach the target value, a virtual short circuit of the operational amplifier OP101 does not hold. The voltage VA shown in FIGS. 13 and 14 is lower than the command voltage Vref, the voltage VB, which is the output voltage of the operational amplifier OP101, is higher than the oscillation voltage Vosc of the triangular wave, and the output of the comparator COMP101 is fixed to the L state. The As a result, the transistor M101 is turned on and the transistor M102 is turned off.

In the above state, if the power supply voltage of the operational amplifier OP101 is VDD, the voltage VB is equal to VDD. Therefore, the voltage Cf across the capacitor C111 in FIGS. 13 and 14 is expressed by the following equations, respectively.
Cf = VDD− {R2 / (R1 + R2)} × Vin (5)
Cf = VDD−Vin (6)
When the operation is switched from this state to the switching power supply, the voltage across the capacitor C111 in FIGS. 13 and 14 shifts from the expressions (5) and (6) to the values shown in the expressions (3) and (4). There is a need. This time delays the settling time. The switch SW1 shown in FIG. 1 solves this settling time delay.

  The switch SW1 is turned on when the switching power supply (switching power supply in FIG. 1) supplies power to the load, and is turned off when supplied with another power supply. Since the switch SW1 is on while the switching power supply is in operation, the voltage across the capacitor C1 is expressed by Equation (3). Further, when the output voltage Vout is not divided by the resistors R1 and R2, it is expressed by Expression (4).

  When switching to another power source, by turning off the switch SW1, the voltage at both ends of the capacitor C1 can be maintained at the value expressed by the equation (3) or the equation (4) even when the other power source is operating. When the operation is switched from the other power source to the switching power source, the switch SW1 is turned on again. Thereby, the charge / discharge time of the capacitor C1 when switching to the switching power supply can be reduced, and the responsiveness is improved. The switch SW1 is turned on / off by a control device that switches power, for example, a CPU.

A voltage waveform at the time of switching the power source will be described.
3A and 3B are diagrams showing voltage waveforms at the time of switching of the power supply. FIG. 3A shows a voltage waveform by a conventional switching power supply, and FIG. 3B shows a voltage waveform by the switching power supply of the present invention. As shown in FIG. 3A, in the conventional switching power supply, when the power supply is switched, a settling time is required due to charging / discharging of the capacitor in the feedback circuit of the operational amplifier. However, in the switching power supply shown in FIG. 1, even if the power supply is switched by holding the voltage of the capacitor C1 when the switching power supply is operating by the switch SW1, as shown in FIG. 3B. In addition, the output voltage Vout changes rapidly.

  In this way, the switch SW1 inserted in series in the feedback circuit holds the charge of the capacitor C1 of the feedback circuit and shortens the settling time of the error signal (voltage VB) output to the comparator COMP1. As a result, the output voltage Vout output to the load can be quickly transferred to the set voltage.

In FIG. 1, the output voltage Vout is divided by the resistors R1 and R2 and input to the operational amplifier OP1, but may be input directly.
A second embodiment of the present invention will be described in detail with reference to the drawings. In the second embodiment, a switch for holding the voltage of the capacitor of the feedback circuit is connected between the resistor R3 and the capacitor C1 with respect to the first embodiment.

  FIG. 4 is a circuit diagram of a switching power supply according to the second embodiment. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. As shown in the figure, the switch SW2 is connected between the resistor R3 and the capacitor C1. The switch SW2 is turned on / off in the same manner as the switch SW1 in FIG. And the voltage of the capacitor | condenser C1 is hold | maintained as demonstrated by Formula (3)-(6). As a result, the same voltage waveform as in FIG. 3 can be obtained, and the output voltage Vout can be quickly changed. In FIG. 4, the output voltage Vout is divided by the resistors R1 and R2 and input to the operational amplifier OP1, but it may be input directly.

  A third embodiment of the present invention will be described in detail with reference to the drawings. In the third embodiment, a switch for holding the voltage of the capacitor of the feedback circuit is connected between the resistor R3 and the inverting input terminal of the operational amplifier OP1 with respect to the first embodiment.

  FIG. 5 is a circuit diagram of a switching power supply according to the third embodiment. 5, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. As shown in the figure, the switch SW3 is connected between the resistor R3 and the inverting input terminal of the operational amplifier OP1. The switch SW3 is turned on / off in the same manner as the switch SW1 in FIG. And the voltage of the capacitor | condenser C1 is hold | maintained as demonstrated by Formula (3)-(6). As a result, the same voltage waveform as in FIG. 3 can be obtained, and the output voltage Vout can be quickly changed. In FIG. 5, the output voltage Vout is divided by the resistors R1 and R2 and input to the operational amplifier OP1, but may be input directly.

A fourth embodiment of the present invention will be described in detail with reference to the drawings. In the fourth embodiment, improvement of responsiveness when the switching power supply is started from a stopped state will be described.
FIG. 6 is a circuit diagram of a switching power supply according to the fourth embodiment. 6, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. As shown in the figure, the switch SW4 is connected in parallel with the capacitor C1.

  When the switching power supply of FIG. 6 is operating, when the relationship between the input side voltage VA and the output side voltage VB of the operational amplifier OP1 is VA> VB, a positive charge is applied to the voltage VA side electrode of the capacitor C1 and the voltage VB. The side electrode is charged with a negative charge. When the operation of the switching power supply is stopped in this state, the charge of the capacitor C1 is held in the same state as described above. Subsequently, when the switching power supply is started and the relationship between the voltage VA and the voltage VB when the target voltage of the output voltage Vout becomes VA <VB, the charge is discharged at the start, and the voltage VA of the capacitor C1 is further discharged. It is necessary to charge a negative charge on the side and a positive charge on the voltage VB side. In the startup of the switching power supply described above, the discharge of the capacitor C1 held when the switching power supply is stopped impairs the responsiveness. In the above, in the operating state before and after the stop state, the target voltage of the output voltage Vout is different, the output voltage Vout after the stop is lower than the output voltage Vout before the stop, and the change from VA> VB to VA <VB Is a precondition. When the switching power supply is stopped, the output of the operational amplifier OP1 is high impedance.

  The switching power supply of FIG. 6 eliminates this delay by the switch SW4. The switch SW4 is turned on when the switching power supply is stopped, and is turned off during operation. That is, when the switching power supply is turned on in a stopped state, the capacitor C1 is discharged. As a result, the discharging operation of the capacitor C1 when the switching power supply is activated can be eliminated, and the responsiveness of the error signal output from the operational amplifier OP1 is improved.

  7A and 7B are diagrams showing voltage waveforms at the time of operation and stop of the power supply. FIG. 7A shows a voltage waveform by a conventional switching power supply, and FIG. 7B shows a voltage waveform by the switching power supply of the present invention. As shown in the figure, in the operating state before and after the stop state, if the target voltage at the time of operation after the output voltage Vout is stopped is lower than the target voltage at the time of operation before the stop, the change from VA> VB to VA <VB Can occur. In this case, in the conventional switching power supply, it is necessary to discharge the charge of the electrode on the voltage VA side of the capacitor C1 and to charge the negative charge. Therefore, as shown in FIG. Time is required for the settling time of the voltage across the capacitor C111 (VB-VA in the figure). However, in the switching power supply of FIG. 6, the switch SW4 is turned on after stopping, so that the charge of the capacitor C1 is discharged (the voltage of VB-VA becomes 0V). Then, during operation after the stop, the switch SW4 is turned off and the capacitor C1 only needs to be charged. Therefore, as shown in FIG. 7B, the settling time of the voltage across the capacitor C1 (VB-VA in the figure). Is shortened.

  As described above, the switch SW4 inserted in parallel with the feedback circuit discharges the charge of the capacitor C1 of the feedback circuit, and shortens the settling time of the error signal (voltage VB) output to the comparator COMP1. As a result, the output voltage Vout output to the load can be quickly transferred to the set voltage.

  Even when the output voltage Vout is higher than the output voltage before the stop in the operating state before and after the stop state, and the change occurs from VA <VB to VA> VB, the settling time is reduced by the same method as described above. Can do.

In FIG. 6, the output voltage Vout is divided by the resistors R1 and R2 and input to the operational amplifier OP1, but it may be input directly.
A fifth embodiment of the present invention will be described in detail with reference to the drawings. Since it suffices if the charge of the capacitor C1 can be discharged when the switching power supply is stopped, in the fifth embodiment, the switch for discharging the charge of the capacitor is a resistor R3 and a capacitor C1 compared to the fourth embodiment. Are connected in parallel to the series circuit.

  FIG. 8 is a circuit diagram of a switching power supply according to the fifth embodiment. 8, the same components as those in FIG. 6 are denoted by the same reference numerals, and the description thereof is omitted. As shown in the figure, the switch SW5 is connected in parallel to a series circuit of a resistor R3 and a capacitor C1.

  The switch SW5 is turned off during operation and turned on when stopped as in the fourth embodiment. Even if the switch SW5 is connected in parallel to the series circuit of the resistor R3 and the capacitor C1, the charge of the capacitor C1 is discharged as in the switching power supply of FIG. Then, similarly to the voltage waveform shown in FIG. 7, the output voltage Vout can be changed quickly. In FIG. 8, the output voltage Vout is divided by the resistors R1 and R2 and input to the operational amplifier OP1, but may be input directly.

A sixth embodiment of the present invention will be described in detail with reference to the drawings. In the sixth embodiment, overshoot when the switching power supply is started is avoided, and the settling time is improved.
FIG. 9 is a circuit diagram of a switching power supply according to the sixth embodiment. 9, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. As shown in the figure, the switch SW6 is connected between the output of the operational amplifier OP1 and the ground.

  13 and 14, when the output voltage of the operational amplifier OP101 is higher than the final value corresponding to the command voltage Vref at the start-up, an overshoot occurs in the output voltage Vout. The switching power supply of FIG. 9 avoids this overshoot by the switch SW6. The switch SW6 is turned on when the switching power supply is stopped and turned off at the time of startup.

  By turning on the switch SW6 while the switching power supply is stopped, the output voltage VB of the operational amplifier OP1 is fixed to 0V. As a result, the initial value of the voltage VB when the switching power supply is activated is set to 0 V, an overshoot when the switching power supply is activated is avoided, and the settling time is improved.

  10A and 10B are diagrams showing voltage waveforms from when the power supply is stopped to when it is started up. FIG. 10A shows a voltage waveform generated by a conventional switching power supply, and FIG. When the output voltage VB of the operational amplifier OP101 at the time of stop is higher than the final value corresponding to the command voltage Vref, an overshoot occurs in the output voltage Vout when starting as shown in FIG. However, in the switching power supply of FIG. 9, when the switch SW6 is turned on at the time of stop and the voltage VB is fixed to 0V, the initial value of the voltage VB when the switching power supply starts is 0V as shown in FIG. Thus, overshoot is avoided and settling time is improved.

  In this way, the switch SW6 between the output of the operational amplifier OP1 and the ground discharges the charge of the capacitor C1 of the feedback circuit, thereby shortening the settling time of the error signal (voltage VB) output to the comparator COMP1. As a result, the output voltage Vout output to the load can be quickly transferred to the set voltage.

In FIG. 9, the output voltage Vout is divided by the resistors R1 and R2 and input to the operational amplifier OP1, but it may be input directly.
A seventh embodiment of the present invention will be described in detail with reference to the drawings. The switching power supplies of the first to sixth embodiments can be combined. By combining one of the first to third embodiments, one of the fourth or fifth embodiment, and three of the sixth embodiment, six types of circuits can be configured. it can. Moreover, when combining two, 11 types of circuits can be comprised. In the seventh embodiment, a case where the second, fourth, and sixth embodiments are combined will be described.

  FIG. 11 is a circuit diagram of a switching power supply according to the seventh embodiment. 11, the same components as those in FIGS. 4, 6, and 9 are denoted by the same reference numerals, and the description thereof is omitted. As shown in the figure, the switch SW7 is connected between the resistor R3 and the capacitor C1 of the feedback circuit. The switch SW8 is connected in parallel with the capacitor C1. The switch SW9 is connected between the output of the operational amplifier OP1 and the ground.

  As described in the second embodiment, the switch SW7 is turned on when the switching power supply of FIG. 11 supplies power to the load, and turned off when supplied by another power supply. When the operation is switched from the other power source to the switching power source in FIG. 11, the switch SW7 is turned on again. Thereby, the electric charge of the capacitor C1 at the time of switching to the switching power supply is held, and the settling time of the error signal (voltage VB) output from the operational amplifier OP1 is improved.

  The switch SW8 is turned on when the switching power supply in FIG. 11 is stopped and turned off when the switching power supply is started. That is, when the switching power supply is turned on in a stopped state, the capacitor C1 is discharged. As a result, the discharging operation of the capacitor C1 when the switching power supply is activated can be eliminated, and the settling time of the error signal output from the operational amplifier OP1 is improved.

  The switch SW9 is turned on when the switching power supply in FIG. 11 is stopped and turned off when the switching power supply is started. By turning on the switch SW9 while the switching power supply is stopped, the output voltage VB of the operational amplifier OP1 is fixed to 0V. As a result, the initial value of the output voltage VB of the operational amplifier OP1 when the switching power supply is activated is set to 0 V, the overshoot at the time of activation of the switching power supply is avoided, and the error signal settling time is improved. Further, the above-described control is not necessarily applied to the switches SW7 to SW9, but the application of the control may be determined by a change in the command voltage Vref and the output voltage Vout.

  Of course, also by the combination of the first to sixth embodiments different from the above, the responsiveness can be improved and the overshoot can be avoided similarly to the above. In FIG. 11, the output voltage Vout is divided by the resistors R1 and R2 and input to the operational amplifier OP1, but may be input directly.

  Further, all the embodiments have been described by taking the synchronous type as an example, but the transistor M2 may be replaced with a diode to be an asynchronous type. In this case, the driver 11 drives only the transistor M1.

It is a circuit diagram of the switching power supply concerning a 1st embodiment. It is the figure which showed the oscillation voltage input into a comparator. It is a figure which shows the voltage waveform at the time of switching of a power supply, (A) shows the voltage waveform by the conventional switching power supply, (B) shows the voltage waveform by the switching power supply of this invention. It is a circuit diagram of the switching power supply concerning a 2nd embodiment. It is a circuit diagram of the switching power supply which concerns on 3rd Embodiment. It is a circuit diagram of the switching power supply which concerns on 4th Embodiment. It is a figure which shows the voltage waveform at the time of operation of a power supply, and a stop, (A) shows the voltage waveform by the conventional switching power supply, (B) shows the voltage waveform by the switching power supply of this invention. It is a circuit diagram of the switching power supply which concerns on 5th Embodiment. It is a circuit diagram of the switching power supply which concerns on 6th Embodiment. It is a figure which shows the voltage waveform from the time of a power supply stop at the time of starting, (A) shows the voltage waveform by the conventional switching power supply, (B) shows the voltage waveform by the switching power supply of this invention. It is a circuit diagram of the switching power supply which concerns on 7th Embodiment. It is a block block diagram of the conventional power supply system. It is a circuit diagram showing an example of a conventional step-down switching power supply. It is the circuit diagram which showed the other example of the conventional step-down type switching power supply.

Explanation of symbols

R1-R3 Resistor C1, C2 Capacitor SW1-SW9 Switch OP1 Op-amp COMP1 Comparator 11 Driver M1, M2 Transistor L1 Coil

Claims (6)

In a switching power supply that supplies power by switching to another power supply according to the load,
An error amplifier that outputs an error signal of a difference between a command voltage for setting an output voltage to be output to the load and a feedback voltage according to the output voltage;
A feedback circuit including a resistor and a capacitor connected between an output and an input of the error amplifier;
A switch for charging and discharging the capacitor,
A comparator that alternately turns on / off a switching element that supplies the power to the load connected in series between a power supply voltage and a ground according to a comparison result between the error signal and an oscillation voltage;
With
The switching is inserted in series in the feedback circuit, and is turned on when the switching power supply supplies power to the load, and is turned off when the other power supply supplies power to the load. Power supply. In a switching power supply that supplies power by switching to another power supply according to the load,
An error amplifier that outputs an error signal of a difference between a command voltage for setting an output voltage to be output to the load and a feedback voltage according to the output voltage;
A feedback circuit including a resistor and a capacitor connected between an output and an input of the error amplifier;
A switch for charging and discharging the capacitor,
A comparator that turns on / off a switch element that supplies the power to the load connected in series with a diode between a power supply voltage and a ground according to a comparison result between the error signal and an oscillation voltage;
With
The switching is inserted in series in the feedback circuit, and is turned on when the switching power supply supplies power to the load, and is turned off when the other power supply supplies power to the load. Power supply.   3. The switching according to claim 1, further comprising a parallel switch inserted in parallel to the capacitor of the feedback circuit, which is turned on when the switching power supply is in a stopped state and turned off when the switching power supply is in operation. Power supply.   In a switching power supply that supplies power by switching to another power supply according to the load,
  An error amplifier that outputs an error signal of a difference between a command voltage for setting an output voltage to be output to the load and a feedback voltage according to the output voltage;
  A feedback circuit including a resistor and a capacitor connected between an output and an input of the error amplifier;
  A switch for charging and discharging the capacitor,
  A comparator that alternately turns on / off a switching element that supplies the power to the load connected in series between a power supply voltage and a ground according to a comparison result between the error signal and an oscillation voltage;
  With
  The switching power supply, wherein the switch is inserted between an output of the error amplifier and the ground, and is turned on when the switching power supply is in a stopped state, and is turned off when the switching power supply is in operation.   In a switching power supply that supplies power by switching to another power supply according to the load,
  An error amplifier that outputs an error signal of a difference between a command voltage for setting an output voltage to be output to the load and a feedback voltage according to the output voltage;
  A feedback circuit including a resistor and a capacitor connected between an output and an input of the error amplifier;
  A switch for charging and discharging the capacitor,
  A comparator that turns on / off a switch element that supplies the power to the load connected in series with a diode between a power supply voltage and a ground according to a comparison result between the error signal and an oscillation voltage;
  With
  The switching power supply, wherein the switch is inserted between an output of the error amplifier and the ground, and is turned on when the switching power supply is in a stopped state, and is turned off when the switching power supply is in operation.   6. The switching according to claim 4, further comprising a parallel switch inserted in parallel to the capacitor of the feedback circuit, which is turned on when the switching power supply is in a stopped state and turned off when the switching power supply is in operation. Power supply.

Images