JPH0570193U - Switching power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a step-up type switching power supply that can prevent damage to switching elements and the like due to inrush current when the power is turned on and can enter an operating state early. [Structure] The charging circuit 3 has an output end 1 of the rectifier circuit 1 on one end side.
1 and the other end is connected to the capacitor 24 to form a unidirectional charging path. The switching circuit 4 is connected between the output terminal 11 of the rectifier circuit 1 and the booster circuit 2, and supplies or cuts off current to the booster circuit 2. The control circuit 5 receives the terminal voltage signal of the capacitor 24, and when the terminal voltage signal is a predetermined value or more, supplies a command signal to the switching circuit 4 to supply current to the booster circuit 2.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a step-up type switching power supply, and more particularly to a switching power supply improved so as to prevent damage to switching elements and the like due to inrush current when the power is turned on and to enter an operating state early.

[0002]

[Prior Art]

 As a conventional technique for preventing a rush current when the power is turned on in a step-up switching power supply, there is one as shown in FIG. In the figure, 1 is a rectifier circuit, 2 is a booster circuit, 311 is a resistor, 411 is a switch, and 5 is a control circuit.

The rectifier circuit 1 rectifies the AC power supply 10 to obtain a rectified output voltage Vr. The switch 411 has one end connected to the output end 11 of the rectifier circuit 1 and the other end connected to the inductor 22 of the booster circuit 2. The switch 411 conducts when it receives the command signal 52. The booster circuit 2 includes a switching element 21, an inductor 22, a diode 23, and a capacitor 24. The switching element 21 is driven on / off at a frequency f2 higher than the frequency f1 of the AC power supply 10. The frequency f2 is set to several kHz or higher. The switching element 21 and the inductor 22 are connected in series, one end of the series connection circuit is connected to the output terminal 11 of the rectifier circuit 1 via the switch 411, and one end of the series connection circuit is connected to the output terminal 12. .. The diode 23 and the capacitor 24 are connected in series, and both ends of the series connection circuit are connected in parallel to the switching element 21, and the terminal voltage of the capacitor 24 is used as the DC output voltage Vo. The resistor 311 is connected in parallel with the switch 411 and limits the inrush current when the power is turned on when the switch 411 is off.

The control circuit 5 uses a DC output voltage Vo equal to the terminal voltage of the capacitor 24 as an input signal 501, supplies a command signal 52 for conducting the switch 411 when the input signal 501 is a predetermined value or more, and A control signal 51 that keeps the input signal 501 constant is supplied to the switching element 21.

When the power is turned on when the switch 411 is not conductive, a charging path is formed by the resistor 311, the inductor 22 and the diode 23. For this reason, the current flowing through the inductor 22 and the diode 23 is limited by the resistor 311, magnetic saturation of the inductor 22 due to the inrush current, which is a problem in the step-up switching power supply, is prevented, and a short-circuit failure when the switching element 21 is turned on. Is also prevented.

When the switch 411 is in a conducting state, the energy stored in the inductor 22 when the switching element 21 is turned on becomes the flyback voltage Vf when the switching element 21 is turned off, which is superimposed on the rectified output voltage Vr and boosted. A direct current output voltage Vo is obtained.

[0007]

[Problems to be solved by the device]

 However, the conventional step-up switching power supply has the following problems. (A) In order to bring the operation state into a usable state at an early stage, it is necessary to reduce the resistance value of the resistor 311 and charge the capacitor 24 at an early stage. However, when the resistance value of the resistor 311 is reduced, the current limiting action is reduced and the inrush current is increased, so that the inductor 22 is easily magnetically saturated. When the switching element 21 performs a switching operation due to the timing when the inductor 22 is magnetically saturated, an excessive current flows to the switching element 21 and the switching element 21 is damaged. (B) In order to avoid the above-mentioned problems, the resistance value of the resistor 311 must be increased. Therefore, the charging of the capacitor 24 is delayed, and the time during which the operating state can be entered is delayed.

Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a step-up type switching power supply which can prevent the switching element and the like from being damaged due to an inrush current at the time of turning on the power and can enter an operating state at an early stage. It is to be.

[0009]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, the present invention is a switching power supply including a rectifier circuit, a booster circuit, a charging circuit, a switching circuit, and a control circuit, wherein the rectifier circuit rectifies an AC power source to rectify the AC power source. A circuit for obtaining an output voltage, wherein the booster circuit includes a switching element, an inductor, a diode, and a capacitor, and the switching element is driven on / off at a frequency higher than the frequency of the AC power supply. , The inductor is connected in series with the switching element, both ends of the series connection circuit are electrically connected to the output end of the rectifier circuit, the diode and the capacitor are connected in series, and both ends of the series connection circuit are connected. Is a circuit that is connected in parallel to the switching element and that uses the terminal voltage of the capacitor as a DC output voltage. Is electrically connected to one of the output terminals of the rectifying circuit, and the other end is connected to the capacitor to form a unidirectional charging path with respect to the capacitor. A circuit that is connected between one of the ends and the booster circuit to supply or cut off a current to or from the booster circuit. The control circuit receives the terminal voltage signal of the capacitor, and receives the terminal voltage signal. Is a circuit that supplies a command signal to the switching circuit to supply current to the booster circuit when is greater than or equal to a predetermined value.

[0010]

[Action]

 In the booster circuit, the switching element is driven on / off at a frequency higher than the frequency of the AC power supply, the inductor is connected in series with the switching element, and both ends of the series connection circuit are connected to the output end of the rectifier circuit via the switching circuit. Since the diode and capacitor are connected in series and both ends of the series connection circuit are connected in parallel to the switching element and the terminal voltage of the capacitor is used as the DC output voltage, the inductor is turned on when the switching element is turned on. The energy stored in the switch becomes a flyback voltage when the switching element is off, and a boosted DC output voltage obtained by superimposing the flyback voltage on the rectified output voltage is obtained.

The charging circuit has one end connected to one of the output ends of the rectifier circuit and the other end connected to the capacitor to form a unidirectional charging path with respect to the capacitor, which is a circuit separate from the inductor. Therefore, the charging time constant can be selected to be a small value without being influenced by the magnetic saturation current of the inductor, and the capacitor can be charged early when the switching power supply is turned on, and the operating state can be entered early. ..

The switching circuit is a circuit that is connected between one of the output terminals of the rectifier circuit and the booster circuit and supplies or cuts off the current to the booster circuit. The control circuit receives the terminal voltage signal of the capacitor. This is a circuit that supplies a command signal to the switching circuit to supply current to the booster circuit when the terminal voltage signal is above a predetermined value.Therefore, charging current flows from the charging circuit to the capacitor. , The current to the booster circuit is cut off by the switching circuit, and the charging of the capacitor progresses to some extent before the current is supplied to the booster circuit through the switching circuit. Therefore, even if the switching element is turned on and off before the charging of the capacitor is completed, inrush current does not flow in the switching element, so the switching element caused by the inrush current and magnetic saturation of the inductor. Short circuit damage is prevented.

[0013]

【Example】

 FIG. 1 is an electric circuit diagram showing a configuration of a switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 8 indicate the same components. 3 is a charging circuit and 4 is a switching circuit.

The charging circuit 3 has one end connected to the output end 11 of the rectifier circuit 1 and the other end connected to the capacitor 24 to form a unidirectional charging path for the capacitor 24. Specifically, it has a resistor 31 and a diode 32, the resistor 31 and the diode 32 are connected in series, and one end of the resistor 31 is connected to the output terminal 11 of the rectifier circuit 1. The cathode side of the terminal 32 is connected to the capacitor 24.

The switching circuit 4 is a circuit that is connected between the output terminal 11 of the rectifier circuit 1 and the booster circuit 2 and supplies or cuts off current from the booster circuit 2. Specifically, the switch 41 is connected between the output end 11 and the inductor 22.

The control circuit 5 uses the DC output voltage Vo, which is the terminal voltage of the capacitor 24, as an input signal 501, and supplies a current to the booster circuit 2 to the switching circuit 4 when the input signal 501 is a predetermined value or more. A command signal 52 to be supplied is supplied. In the drawing, the control signal 51 for making the input signal 501 constant is further supplied to the switching element 21.

As described above, in the booster circuit 2, the switching element 21 is driven on / off at the frequency f2 higher than the frequency f1 of the AC power supply 10, and the inductor 22 is connected in series with the switching element 21. Both ends of the series connection circuit are electrically connected to the output end 11 of the rectifier circuit 1 through the switching circuit 4, the diode 23 and the capacitor 24 are connected in series, and both ends of the series connection circuit are connected in parallel to the switching element 21. Since the terminal voltage of the capacitor 24 is used as the DC output voltage Vo, the energy stored in the inductor 22 when the switching element 21 is turned on becomes the flyback voltage Vf when the switching element 21 is turned off, and the rectified output is obtained. A boosted DC output voltage Vo obtained by superimposing the flyback voltage Vf on the voltage Vr is obtained.

The charging circuit 3 has one end connected to the output end 11 of the rectifier circuit 1 and the other end connected to the capacitor 24 to form a unidirectional charging path for the capacitor 24. Since this is a separate circuit, the charging time constant is selected to be a small value without being influenced by the magnetic saturation current of the inductor 22, the capacitor 24 is charged early when the power is turned on, and the operating state is set early. Can enter. The charging time constant can be reduced by selecting a small value for the resistor 31.

The switching circuit 4 is a circuit that is connected between one output terminal 11 of the rectifier circuit 1 and the booster circuit 2 to supply or cut off current to the booster circuit 2. The control circuit 5 is a capacitor. The terminal voltage signal of 24 is input, and when the terminal voltage signal is equal to or higher than a predetermined value, the switching circuit 4 supplies a command signal for supplying current to the booster circuit 2. When the power is turned on when the charging current is flowing into 24, the current to the booster circuit 2 is cut off by the switching circuit 4, and the current is supplied to the booster circuit 2 through the switching circuit 4 after the charging of the capacitor 24 progresses to some extent. .. Therefore, even if the switching element 21 is turned on and off before the charging of the capacitor 24 is completed, no inrush current flows in the switching element 21, which results from the inrush current and the magnetic saturation of the inductor 22. Short circuit damage of the switching element 21 is prevented.

When the DC output voltage Vo becomes higher than the rectified output voltage Vr, the charging of the capacitor 24 by the charging circuit 3 ends. The diode 32 absorbs this reverse bias, and the reverse current due to the direct current output voltage Vo is prevented.

FIG. 2 is an electric circuit diagram showing the configuration of another embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same components.

The switching circuit 4 is connected between the output terminal 11 of the rectifier circuit 1 and the charging circuit 3 and supplies or cuts off current from the charging circuit 3. In this embodiment, the changeover switch 42 is used to switch between the booster circuit 2 and the charging circuit 3. The control circuit 5 supplies a command signal 52 for supplying a current to the booster circuit 2 to the switching circuit 4 when the input signal 501 is a predetermined value or more. When the input signal 501 is less than the predetermined value, the switching circuit 4 supplies a current to the charging circuit 3 to charge the capacitor 24. When the input signal 501 is a predetermined value or more, a current is supplied to the booster circuit 2 through the switching circuit 4, the rectified output voltage Vr is superimposed on the flyback voltage Vf, and a boosted DC output voltage Vo is obtained.

FIG. 3 is an electric circuit diagram showing another embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIGS. 1 and 2 denote the same components.

The control circuit 5 includes a target setting circuit 53, an error detection circuit 54, a current detection circuit 55, a differential amplifier circuit 56, and a pulse width control circuit 57.

The target setting circuit 53 includes a reference voltage signal generator 530 that generates a reference voltage signal, receives the rectified output voltage signal 502 and the DC output voltage signal 501 as input signals, and outputs the first output signal 531 and And a second output signal 532. The first output signal 531 is derived from the reference voltage signal. The second output signal 532 is derived from the DC output voltage signal 501. Either the first output signal 531 or the second output signal 532 is adjusted so that the DC output voltage Vo becomes higher than the rectified output voltage Vr by following the increase and decrease in the entire rectified output voltage Vr. Change. FIG. 5 is a characteristic diagram showing an example of the first output signal 531. The first output signal 531 follows the rectified output voltage signal 502 and is set so that the DC output voltage Vo is higher than the rectified output voltage Vr. The same applies to the second output signal 532.

The error detection circuit 54 receives the first output signal 531, the second output signal 532, and the rectified output voltage signal 502, and compares the first output signal 531 with the second output signal 532. An error detection signal 541 having a waveform similar to that of the rectified output voltage signal 502 is output. Specifically, the error amplification circuit 542 compares the first output signal 531 and the second output signal 532 and outputs the error signal 543, and the multiplication circuit 544 outputs the error signal 543 and the rectified output voltage signal 502. Is multiplied by to obtain the error detection signal 541. The error amplification circuit 542 and the multiplication circuit 544 can be configured by a differential amplification circuit using an operational amplifier, a multiplication circuit, or the like.

The current detection circuit 55 detects a current flowing through the inductor 22 and outputs a current detection signal 551.

The differential amplifier circuit 56 receives the error detection signal 541 and the current detection signal 551, compares the two signals, and outputs a differential signal 561 that causes the current detection signal 551 to follow the error detection signal 541.

The pulse width control circuit 57 receives the differential signal 561 and supplies the control signal 371 for controlling the switching element 21 so as to minimize the differential signal 561 to the switching element 21.

The target setting circuit 53 includes a reference voltage signal generation unit 530 that generates a reference voltage signal, the rectified output voltage signal 502 and the DC output voltage signal 501 are input, and the first output signal 531 and the first output signal 531 are input. Two output signals 532 are output, the first output signal 531 is obtained from the reference voltage signal, the second output signal 532 is obtained from the DC output voltage signal 501, and the first output signal 531 and the second output signal 531 are obtained. One of the output signals 532 follows the increase / decrease of the rectified output voltage Vr in the entire voltage range and is changed so that the DC output voltage Vo becomes higher than the rectified output voltage Vr. The first output signal 531, the second output signal 532, and the rectified output voltage signal 502 are input, the first output signal 531 and the second output signal 532 are compared, and the rectified output voltage signal 502 and the phase are compared. Since the error detection signal 541 having a similar waveform is output, when the reference voltage signal is changed, the second output signal 532 changes following the first output signal 531 and the DC output voltage Vo also changes at the same time. To do. When the DC output voltage signal 501 is changed, the second output signal 532 is controlled to match the first output signal 531 and the DC output voltage Vo changes in the process of matching. This satisfies the requirement that the DC output voltage Vo is higher than the rectified output voltage Vr, which is the requirement for power factor improvement.

The current detection circuit 55 detects the current flowing through the inductor 22 and outputs the current detection signal 551, and the differential amplifier circuit 56 compares the error detection signal 541 and the current detection signal 551 to obtain the current. A differential signal 561 that causes the detection signal 551 to follow the error detection signal 541 is output, and the pulse width control circuit 57 outputs to the switching element 21 a control signal 371 that controls the switching element 21 so as to minimize the differential signal 561. Since it is supplied, the DC output voltage Vo is adjusted to a voltage corresponding to the first output signal 531 and the input current changes following the AC input voltage. It becomes equivalent to the resistance load and can improve the power factor.

As a result, when the rectified output voltage Vr drops, the DC output voltage Vo also drops, so that the current flowing through the switching element 21 for boosting can be reduced, and the power of the switching element 21 can be reduced. Loss can be reduced.

Although the DC output voltage Vo fluctuates, since a DC-DC converter is generally connected in the subsequent stage, the DC-DC converter absorbs the fluctuation of the DC output voltage Vo and finally stabilizes. DC output can be obtained.

The target setting circuit 53 can be configured to change the DC output voltage signal 501 according to the rectified output voltage signal 502. FIG. 4 is a circuit diagram showing a specific example thereof. Reference numeral 530 is a reference voltage signal generator, and 544 is a DC output voltage adjuster. The rectified output voltage Vr is applied between the terminals 535 and 536, and the DC output voltage Vo is applied between the terminals 537 and 536.

The reference voltage signal generator 530 generates a reference voltage Vk that serves as a reference for increasing / decreasing the DC output voltage Vo, and outputs it as a first output signal 531. The reference voltage Vk is obtained from the battery B1. The positive electrode of the battery B1 is connected to the terminal 538. The reference voltage Vk may be obtained by forming a DC constant voltage circuit and dividing the DC constant voltage with a resistance voltage dividing circuit.

The DC output voltage adjusting unit 534 changes the voltage division ratio of the resistor that divides the DC output voltage Vo according to the rectified output voltage signal 502, and outputs the divided voltage as the second output signal 532. This embodiment has a diode D1, a capacitor C1, resistors R1 to R6, an operational amplifier IC1 and a battery B2. The diode D1 and the capacitor C1 are connected in series, and both ends of the series connection are connected to the terminals 535 and 536. The resistor R1 and the resistor R2 are connected in series, and both ends of which are connected in series are connected to the capacitor C1. The connection point between the resistors R1 and R2 is connected to the negative input terminal of the operational amplifier IC1 and supplies a divided voltage Vin obtained by dividing the rectified output voltage Vr to the operational amplifier IC1. The battery B2 is connected to the positive input terminal of the operational amplifier IC1 and supplies the reference voltage Vk to the operational amplifier IC1. The resistor R3 is connected between the output terminal and the negative input terminal of the operational amplifier IC1. The resistor R4 has one end connected to the output end of the operational amplifier IC1 and the other end connected to a connection point between the resistors R5 and R6. The resistors R5 and R6 are connected in series, and both ends of which are connected in series are connected to the terminals 537 and 536. The connection point between the resistors R5 and R6 is connected to the terminal 539, and the divided voltage VR6 obtained by dividing the DC output voltage Vo is supplied as the second output signal 532. The operational amplifier IC1 constitutes an inverting amplifier circuit, and the output voltage Vout decreases as the divided voltage Vin increases. Therefore, the terminal voltage VR5 of the resistor R5 rises due to an increase in the current flowing through the resistor R4 when the rectified output voltage Vr rises, that is, the output voltage Vout decreases. Further, the terminal voltage VR5 of the resistor R5 decreases due to the decrease in the current flowing through the resistor R4 when the rectified output voltage Vr decreases, that is, the output voltage Vout increases. Therefore, if the DC output voltage Vo is constant, the piezoelectric voltage VR6 of the resistor R6 decreases as the terminal voltage VR5 increases, and increases as the terminal voltage VR5 decreases.

The error detection circuit 54 operates so as to match the divided voltage VR6 at the terminal 539 with the reference voltage V k at the terminal 538, so that the change in the divided voltage VR6 is substantially the first output signal 531. And the DC output voltage Vo is finally adjusted to the target DC output voltage. That is, when the rectified output voltage Vr increases, the divided voltage VR6 decreases, and when the rectified output voltage Vr decreases when the DC output voltage Vo increases in the process of making the divided voltage VR6 equal to the reference voltage Vk, The divided voltage VR6 rises, and the DC output voltage Vo is lowered in the process of making the divided voltage VR6 equal to the reference voltage Vk. Thereby, the DC output voltage Vo is adjusted to be higher than the rectified output voltage Vr.

The target setting circuit 53 can also be configured to change the reference voltage signal according to the rectified output voltage signal 502. FIG. 6 shows a specific example thereof. In the figure, the same reference numerals as those in FIGS. 3 and 4 denote the same components. Hereinafter, description will be given with reference to FIGS. 3, 4, 5, and 6.

The reference voltage signal generator 530 changes the reference voltage Vk according to the rectified output voltage signal 502 and outputs the first output signal 531. In this embodiment, it has a diode D1, a capacitor C1, a resistor R1 and a resistor R2, a resistor R7, and a battery B3. The diode D1, the resistor R1 and the resistor R2 are connected in series, and both ends of the series connection circuit are connected to the terminals 535 and 536. The capacitor C1 is connected in parallel to the series connection circuit of the resistor R1 and the resistor R2. The resistor R2 generates a divided voltage Vin obtained by dividing the rectified output voltage Vr. The resistor R7 and the battery B3 are connected in series, and both ends connected in series are connected to the resistor R2. One end of the resistor R7 is connected to the terminal 538, and the reference voltage Vk is supplied to the terminal 538. When the divided voltage Vin is higher than the voltage Vref, the reference voltage Vk becomes higher than the voltage Vref when a current flows from the resistor R1 to the battery B3. When the divided voltage Vin is lower than the voltage Vref, the battery B3 is supplied. Current flows from the resistor R2 into the resistor R2 and becomes lower than the voltage Vref.

The DC output voltage adjusting unit 534 has a resistor R5 and a resistor R6, and divides the DC output voltage Vo by resistance. The connection point of the resistors R5 and R6 is connected to the terminal 539, and the divided voltage VR6 is output to the terminal 539 as the second output signal 532.

Since the error detection circuit 54 operates so as to match the first output signal 531 and the second output signal 532, the second output signal 532 follows the first output signal 531. It changes, and finally the DC output voltage Vo is adjusted to the target DC output voltage. With this, it is possible to obtain the same effects as those of the other embodiments.

Even if the target setting circuit 53 is configured to change the first output signal 531 or the second output signal 532 stepwise as shown in FIG. You can get the effect.

The embodiments of FIGS. 3 to 6 can also be applied to a switching power supply that obtains a constant voltage corresponding to various types of AC power supplies having different power supply voltages. FIG. 7 shows an example of the case where the power source voltage of the AC power source is 100 V and 200 V in common. The reference voltage Vref1 is a reference voltage for 100 V, and Vref2 is a reference voltage for 200 V. As shown in the figure, since the reference voltages Vref1 and Vref2 are switched with hysteresis, it is possible to switch the DC output Vo without causing hunting regardless of which AC power supply is used. Instead of changing the reference voltage, the DC output voltage signal may be changed.

[0044]

[Effect of the device]

 As described above, according to the present invention, the following effects can be obtained. (A) In the step-up circuit, the switching element is driven on / off at a frequency higher than the frequency of the AC power source, the inductor is connected in series with the switching element, and both ends of the series connection circuit are rectified by a switching circuit. Since the diode and the capacitor are connected in series and both ends of the series connection circuit are connected in parallel to the switching element and the terminal voltage of the capacitor is used as the DC output voltage, the rectified output voltage It is possible to provide a switching power supply that can obtain a boosted DC output voltage in which the flyback voltage of the inductor is superposed on. (B) The charging circuit has one end connected to one of the output ends of the rectifier circuit and the other end connected to the capacitor to form a unidirectional charging path for the capacitor, which is separate from the inductor. Since it is a circuit, it is possible to provide a switching power supply that can enter an operating state at an early stage. (C) The switching circuit is a circuit that is connected between one of the output terminals of the rectifier circuit and the booster circuit to supply or cut off the current to the booster circuit. The control circuit receives the terminal voltage signal of the capacitor. This is a circuit that supplies a command signal that causes the switching circuit to supply current to the booster circuit when the terminal voltage signal that is input is at or above a specified value.Therefore, short-circuiting of the switching element caused by inrush current and magnetic saturation of the inductor A switching power supply that can prevent damage can be provided.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of a switching power supply according to the present invention.

FIG. 2 is an electric circuit diagram of another embodiment of the switching power supply according to the present invention.

FIG. 3 is an electric circuit diagram of another embodiment of the switching power supply according to the present invention.

FIG. 4 is an electric circuit diagram showing an example of a target setting circuit used in the switching power supply according to the present invention.

FIG. 5 is an input / output characteristic diagram of a reference voltage generating circuit of a switching power supply according to the present invention.

FIG. 6 is an electric circuit diagram showing an example of a target setting circuit used in the switching power supply according to the present invention.

FIG. 7 is another input / output characteristic diagram of the reference voltage generating circuit of the switching power supply according to the present invention.

FIG. 8 is an electric circuit diagram showing a configuration of a conventional step-up switching power supply.

[Explanation of symbols]

 1 Rectifier circuit 11, 12 Output terminal 2 Booster circuit 21 Switching element 22 Inductor 23 Diode 24 Capacitor 3 Charging circuit 4 Switching circuit 5 Control circuit 5 501 Input signal 51 Control signal 52 Command signal Vr Rectified output voltage Vo DC output voltage

Claims (3)

[Scope of utility model registration request] 1. A rectifying circuit, a boosting circuit, a charging circuit,
A switching power supply having a switching circuit and a control circuit, wherein the rectifier circuit is a circuit that rectifies an AC power supply to obtain a rectified output voltage, and the booster circuit includes a switching element, an inductor, and
A diode and a capacitor, wherein the switching element is turned on / off at a frequency higher than the frequency of the AC power supply.
It is driven off, the inductor is connected in series with the switching element, both ends of the series connection circuit are electrically connected to the output end of the rectifier circuit, the diode and the capacitor are connected in series, and the series connection circuit is connected. Both ends of are connected in parallel to the switching element, is a circuit that uses the terminal voltage of the capacitor as a DC output voltage, the charging circuit, one end side is conducted to one of the output end of the rectifier circuit, the other end side The switching circuit is connected to the capacitor to form a unidirectional charging path with respect to the capacitor, and the switching circuit is connected between one of the output terminals of the rectifying circuit and the boosting circuit, The control circuit receives a terminal voltage signal of the capacitor, and the terminal voltage signal is equal to or more than a predetermined value. Switching power supply is a circuit for supplying a command signal for supplying current to said boosting circuit to said switching circuit when it is. 2. The charging circuit includes a resistor and another diode.
2. The switching power supply according to claim 1, wherein the switching power supply comprises a resistor, and the resistor and the other diode are connected in series. 3. The switching circuit is a circuit that is connected between one of the output terminals of the rectifying circuit and the charging circuit to supply or cut off current to the charging circuit, and the control circuit is The switching power supply according to claim 1 or 2, which is a circuit that supplies the command signal to the switching circuit when an input signal is less than a predetermined value.