JPH0570192U - Switching power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a step-up switching power supply with improved efficiency by reducing the power loss of a switching element that is in parallel with a current limiting resistor. [Configuration] Inductor 22 is the first switching element 2
1 is connected in series to the output terminals 11 and 12 of the rectifier circuit 1. A diode 23, a capacitor 24 and a current limiting circuit 25 are connected in series with each other and in parallel with the switching element 21. The current limiting circuit 25 includes a resistor 252 and a second switching element 251. The terminal voltage Vc of the capacitor 24 is set to the DC output voltage V
Use as o. The control circuit 3 turns on the second switching element 251 at the timing when the terminal voltage Vc of the capacitor 24 becomes a predetermined value or more.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a step-up type switching power supply that boosts a rectified output to obtain a direct current output, and more particularly, to a technique for reducing power loss in a steady state and suppressing an inrush current when the power is turned on.

[0002]

[Prior Art]

 As a conventional technique for preventing a rush current when the power is turned on in the 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, and 3 is a control circuit.

The rectifier circuit 1 rectifies the AC power supply 10 to obtain a rectified output voltage Vr. The booster circuit 2 includes a first switching element 21, an inductor 22, a diode 23, a capacitor 24, and a current limiting circuit 25. The first 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, preferably 50 kHz. The inductor 22, the current limiting circuit 25, and the first switching element 21 are connected in series, and both ends connected in series are connected to the output terminals 11 and 12 of the rectifier circuit 1. A diode 23 and a capacitor 24 are connected in series, and both ends of which are connected in series are connected in parallel to the first switching element 21 so that a smoothed DC output voltage Vo is obtained from both ends of the capacitor 24. Is becoming Therefore, the energy accumulated in the inductor 22 when the first switching element 21 is turned on becomes the flyback voltage Vf when the first switching element 21 is turned off, and the DC output in which the flyback voltage Vf is superimposed on the rectified output voltage Vr is output. The voltage Vo is obtained. The current limiting circuit 25 includes a resistor 252 and a second switching element 251, and limits the current by the presence or absence of a short circuit across the resistor 252 by the second switching element 251.

The control circuit 3 uses the DC output voltage Vo as an input signal 301, supplies a control signal 31 for stabilizing the DC output voltage Vo to the first switching element 21, and charges the capacitor 24 to output a DC output. When the voltage Vo is equal to or higher than a predetermined value, the current limiting circuit 25 is supplied with the release signal 32 for releasing the limitation of the current flowing through the first switching element 21 and the capacitor 24. Therefore, the inrush current flowing through the switching element 21, the inductor 22 and the capacitor 24 when the power is turned on is limited by the resistor 252. Therefore, the magnetic saturation of the inductor 22 due to the inrush current, which is a problem in the switching power supply, is prevented, and the short-circuit failure of the first switching element 21 is prevented.

[0005]

[Problems to be solved by the device]

 However, in the switching power supply of the conventional example, the current I1 flowing through the second switching element 251 constituting the current limiting circuit 25 is the first switching element 21 when the rush current at the time of power-on disappears. Current I2, the pulsating current I3 flowing through the capacitor 24, and the load current I4, I1 = I2 + I3 + I4. For this reason, the loss in the second switching element 251 constituting the current limiting circuit 25 becomes large, and the power efficiency of the switching power supply decreases.

Therefore, an object of the present invention is to solve the above-mentioned problems, to prevent the switching element from being damaged by an inrush current, and to provide a switching power supply with a small power loss in a steady state.

[0007]

[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, and a control circuit, wherein the rectifier circuit is a circuit that rectifies an AC power supply to obtain a rectified output, The step-up circuit includes a first switching element, an inductor, a diode, a capacitor, and a current limiting circuit, and the first switching element is on / off driven at a frequency higher than the frequency of the AC power supply. The inductor is connected in series with the first switching element, both ends of the series connection circuit are connected to the output terminal of the rectification circuit, and the current limiting circuit is connected in parallel with the resistor and the second switching element. A circuit, the diode, the capacitor, and the current limiting circuit are connected in series, and both ends of the series connection circuit are connected to the first switching element. Is a circuit that is connected in parallel with the capacitor and uses the terminal voltage of the capacitor as a DC output voltage. The control circuit is a circuit that turns on the second switching element at a timing when the terminal voltage becomes a predetermined value or more. Is.

[0008]

[Action]

 In the step-up circuit, the first 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 first switching element, and both ends of the series connection circuit are output terminals of the rectifier circuit. , A diode, a capacitor and a current limiting circuit are connected in series, and both ends of the series connection circuit are connected in parallel to the first switching element, and the terminal voltage of the capacitor is used as the DC output voltage. Therefore, the energy stored in the inductor when the first switching element is on becomes the flyback voltage when the first switching element is off, and the voltage that superimposes the flyback voltage on the rectified output is stored in the capacitor and boosted. DC output voltage can be obtained.

The current limiting circuit is composed of a parallel connection circuit of a resistor and a second switching element, a capacitor and a current limiting circuit are connected in series, and the control circuit sets the terminal voltage of the capacitor to a predetermined value or more at a predetermined timing. Since the switching element of No. 2 is turned on, the inrush current is suppressed until the terminal voltage of the capacitor reaches the predetermined voltage, by the current limiting action of the resistance against the current flowing into the capacitor.

Since the diode, the capacitor and the current limiting circuit are connected in series and both ends of the series connection circuit are connected in parallel to the first switching element, the second switching element is turned on. In the steady state after that, the current flowing through the second switching element is at least a value obtained by subtracting the current flowing through the first switching element from the current flowing through the inductor. Therefore, all the current flowing through the inductor is reduced in power loss in the second switching element and efficiency is higher than that in the conventional technique in which the current is flowing in the second switching element.

In the preferred embodiment, the DC output voltage is obtained across a series connection of a capacitor and a current limiting circuit. In the case of this configuration, in the steady state, the current flowing through the second switching element is only the fluctuation due to the charge / discharge ripple of the capacitor, the power loss of the second switching element is further reduced, and the efficiency of the switching power supply is reduced. Will be even higher.

[0012]

【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.

The booster circuit 2 includes a first switching element 21, an inductor 22, a diode 23, a capacitor 24, and a current limiting circuit 25. The first switching element 21 is driven on / off at a frequency f2 higher than the frequency f1 of the AC power supply. The inductor 22 is connected in series with the first switching element 21, and both ends of the series connection circuit are connected to the output terminals 11 and 12 of the rectifier circuit 1. The current limiting circuit 25 is composed of a parallel connection circuit of a resistor 252 and a second switching element 251. The diode 23, the capacitor 24, and the current limiting circuit 25 are connected in series, and both ends of the series connection circuit are connected in parallel to the first switching element 21. Then, the terminal voltage Vc of the capacitor 24 is used as the DC output voltage Vo.

The control circuit 3 turns on the second switching element 251 at the timing when the terminal voltage Vc of the capacitor 24 becomes a predetermined value or more. As a control method, the terminal voltage Vc is monitored, and when the terminal voltage Vc exceeds a predetermined value, the second switching element 251 is turned on, and a predetermined delay after the AC power supply 10 is turned on. There may be a method of turning on the second switching element 251 with time. The illustrated control circuit 3 uses the DC output voltage Vo as the first input signal 301, the terminal voltage Vc of the capacitor 24 as the second input signal 302, and outputs the control signal 31 for stabilizing the first input signal 301. The first switching element 21 is supplied with the release signal 32 for releasing the limitation of the current Ic flowing through the capacitor 24 to the current limiting circuit 25 when the second input signal 302 has a predetermined value or more. Is becoming

As described above, in the booster circuit 2, the first 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 first switching element 21. Both ends of the series connection circuit are connected to the output end of the rectifier circuit 1, the diode 23, the capacitor 24 and the current limiting circuit 25 are connected in series, and both ends of the series connection circuit are the first switching element. Since the terminal voltage Vc of the capacitor 24 is used as the DC output voltage Vo, the energy accumulated in the inductor 22 when the first switching element 21 is turned on is connected to the first switching element 21. The flyback voltage Vf is generated when the switch is turned off, and a voltage obtained by superposing the flyback voltage Vf on the rectified output voltage Vr is applied to the capacitor 24. The accumulated and boosted DC output voltage Vo is obtained.

The current limiting circuit 25 is composed of a circuit in which a resistor 252 and a second switching element 251 are connected in parallel, the capacitor 24 and the current limiting circuit 25 are connected in series, and the control circuit 3 sets the terminal voltage Vc of the capacitor 24 to a predetermined value. Since the second switching element 251 is turned on at the timing when the value becomes equal to or more than the value, the current limiting action by the resistor 252 acts on the current flowing into the capacitor 24 until the terminal voltage Vc of the capacitor 24 reaches a predetermined voltage. Inrush current is suppressed.

Further, since the diode 23, the capacitor 24 and the current limiting circuit 25 are connected in series, and both ends of the series connection circuit are connected in parallel to the first switching element 21, the second switching In a steady state after the element 251 is turned on, the current I3 flowing through the second switching element 251 is at least a value obtained by subtracting the current I2 flowing through the first switching element 21 from the current I1 flowing through the inductor 22. become. Therefore, all the current I1 flowing in the inductor 22 is smaller in power loss in the second switching element 251 and efficiency is higher than in the conventional technique in which the current I1 is flowing in the second switching element 251.

In the embodiment, the DC output voltage Vo is obtained from both ends of the series connection circuit of the capacitor 24 and the current limiting circuit 25. In the case of this configuration, in the steady state, the current I3 flowing through the second switching element 251 is only the variation due to the charge / discharge ripple of the capacitor 24. That is, I3 = I1- (I2 + I4). Therefore, the power loss of the second switching element 251 is further reduced, and the efficiency of the switching power supply is further increased.

FIG. 2 is a circuit diagram showing another embodiment of the switching power supply according to the present invention. In this embodiment, the current limiting circuit 25 is inserted in the subsequent stage of the first switching element 21, and the terminal voltage Vc of the capacitor 24 is directly used as the DC output voltage Vo. In the case of this embodiment, the current I3 flowing through the second switching element 251 has a value obtained by subtracting the current I2 flowing through the first switching element 21 from the current I1 flowing through the inductor 22.

FIG. 3 is a block 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 3 includes a target setting circuit 33, an error detection circuit 34, a current detection circuit 35, a differential amplifier circuit 36, and a pulse width control circuit 37.

The target setting circuit 33 includes a reference voltage signal generation unit 330 that generates the reference voltage signal 331, and the rectified output voltage signal 303 and the DC output voltage signal (first input signal) 301 are input to the target setting circuit 33. The first output signal 332 and the second output signal 321 are output. The first output signal 332 is derived from the reference voltage signal 331. The second output signal 321 is obtained from the DC output voltage signal (first input signal) 301. Either one of the first output signal 332 and the second output signal 321 may follow the increase / decrease in the entire voltage range of the rectified output voltage Vr so that the DC output voltage Vo becomes higher than the rectified output voltage Vr. Changes to. FIG. 5 is a characteristic diagram showing an example of the first output signal 332. The first output signal 332 follows the rectified output signal 31 and is set so that the DC output voltage Vo becomes larger than the rectified output voltage Vr. The second output signal 321 is similar.

The error detection circuit 34 receives the first output signal 332, the second output signal 321, and the rectified output voltage signal 303, and compares the first output signal 332 with the second output signal 321. An error detection signal 341 having a waveform similar to that of the rectified output voltage signal 303 is output. Specifically, the error amplification circuit 342 compares the first output signal 332 and the second output signal 321 and outputs the error signal 343, and the multiplication circuit 344 outputs the error signal 343 and the rectified output voltage signal 303. Is multiplied to obtain an error detection signal 341. The error amplification circuit 342 and the multiplication circuit 344 can be configured by a differential amplification circuit using an operational amplifier, a multiplication circuit, or the like.

The current detection circuit 35 detects the current flowing through the inductor 22 and outputs a current detection signal 351.

The differential amplifier circuit 36 receives the error detection signal 341 and the current detection signal 351, and compares the two signals and outputs a differential signal 361 that causes the current detection signal 351 to follow the error detection signal 341.

The pulse width control circuit 37 receives the differential signal 361 and supplies the control signal 371 for controlling the switching element 21 so as to minimize the differential signal 361 to the switching element 21.

The target setting circuit 33 includes a reference voltage signal generation unit 330 that generates a reference voltage signal 331, and receives the rectified output voltage signal 303 and the DC output voltage signal (first input signal) 301, The first output signal 332 and the second output signal 321 are output, the first output signal 332 is obtained from the reference voltage signal 331, and the second output signal 321 is the DC output voltage signal (first Input signal) 301, one of the first output signal 332 and the second output signal 321 follows the increase / decrease in the entire voltage range of the rectified output voltage Vr, and the DC output voltage Vo is equal to the rectified output voltage Vo. The error detection circuit 34 is input with the first output signal 332, the second output signal 321, and the rectified output voltage signal 303, and the error detection circuit 34 receives the first output signal 332 and the second output signal 332. Since the error detection signal 341 having a similar waveform to the rectified output voltage signal 303 is output by comparing with the force signal 321, the second output signal 321 is changed to the first output signal 332 when the reference voltage signal 331 is changed. The DC output voltage Vo also changes at the same time. Further, when the DC output voltage signal (first input signal) 301 is changed, the second output signal 321 is controlled so as to match the first output signal 332, and in the process of matching, the DC output voltage Vo Changes. 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 35 detects the current flowing through the inductor 22 and outputs the current detection signal 351. The differential amplifier circuit 36 compares the error detection signal 341 and the current detection signal 351 to determine the current. The pulse width control circuit 37 outputs a differential signal 361 that causes the detection signal 351 to follow the error detection signal 341, and the pulse width control circuit 37 controls the switching element 21 to control the switching element 21 so as to minimize the differential signal 361. Since it is supplied, the DC output voltage Vo is adjusted to a voltage corresponding to the first output signal 332, 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 33 can be configured to change the DC output voltage signal 30 17 according to the rectified output voltage signal 303. FIG. 4 is a circuit diagram showing a specific example of the target setting circuit. Reference numeral 330 is a reference voltage signal generator, and 334 is a DC output voltage adjuster. The rectified output voltage Vr is applied between the terminals 335 and 336, and the DC output voltage Vo is applied between the terminals 337 and 336.

The reference voltage signal generator 330 generates a reference voltage Vk that serves as a reference for increasing or decreasing the DC output voltage Vo, and outputs the reference voltage Vk as a first output signal 332. The reference voltage Vk is obtained from the battery B1. The positive electrode of the battery B1 is connected to the terminal 338. 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 334 changes the voltage division ratio of the resistor that divides the DC output voltage Vo according to the rectified output voltage signal 303, and outputs the divided voltage as the second output signal 321. 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 terminal 335 and the terminal 336. 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 337 and 336. The connection point between the resistors R5 and R6 is connected to the terminal 339, and the divided voltage VR6 obtained by dividing the DC output voltage Vo is supplied as the second output signal 321. 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.

Since the error detection circuit 34 connected in the subsequent stage operates so as to match the divided voltage VR6 at the terminal 339 with the reference voltage Vk at the terminal 338, the change in the divided voltage VR6 is substantially the same. The output signal 332 changes to 1 and the DC output voltage Vo is finally adjusted to the target DC output voltage. That is, when the rectified output voltage Vr rises, the piezoelectric voltage VR6 decreases, and in the process of making the divided voltage VR6 equal to the reference voltage Vk, the DC output voltage Vo increases and when the rectified output voltage Vr decreases, The pressure 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. As a result, the DC output voltage Vo is adjusted to be higher than the rectified output voltage Vr, and the same effect as that of the embodiment of FIG. 1 can be obtained.

The target setting circuit 33 can also be configured to change the reference voltage signal 331 according to the rectified output voltage signal 303. FIG. 6 is a circuit diagram showing a concrete example of the target setting circuit. 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, and 6.

The reference voltage signal generator 330 changes the reference voltage Vk according to the rectified output voltage signal 303 and outputs the first output signal 332. 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 335 and 336. 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 338 and supplies the reference voltage Vk to the terminal 338. 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 334 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 339, and the divided voltage VR6 is output to the terminal 339 as the second output signal 321.

Since the error detection circuit 34 connected in the subsequent stage operates so as to match the first output signal 332 and the second output signal 321, the second output signal 321 outputs the first output signal 321. It changes following the signal 332, and finally the DC output voltage Vo is adjusted to the target DC output voltage. This makes it possible to obtain the same effects as those of the other embodiments.

Even if the target output voltage setting circuit 33 is configured to change the first output signal 322 or the second output signal 32 1 in a stepwise manner, it is possible to obtain the same operational effect as the other embodiments. it can.

The present invention can 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 shares 100 volt and 200 volt. The reference voltage Vref1 is for 100 volts, and Vref2 is for 200 volts. As shown in the figure, since the switching between the reference voltages Vref1 and Vref2 is provided with hysteresis, the DC output voltage Vo can be switched without hunting regardless of which AC power source is used. Instead of changing the reference voltage, the DC output voltage signal may be changed.

[0041]

[Effect of the device]

 As described above, according to the present invention, the following effects can be obtained. (A) In the booster circuit, the first switching element is ON / OFF driven at a frequency higher than the frequency of the AC power supply, the inductor is connected in series with the first switching element, and both ends of the series connection circuit are connected. It is connected to the output terminal of the rectifier circuit, the diode, the capacitor and the current limiting circuit are connected in series, and both ends of the series connection circuit are connected in parallel to the first switching element, and the terminal voltage of the capacitor is changed to DC. Since it is used as the output voltage, it is possible to provide a step-up switching power supply. (B) The current limiting circuit is composed of a resistor and the second switching element connected in parallel, the capacitor and the current limiting circuit are connected in series, and the control circuit waits for the terminal voltage of the capacitor to rise above the specified value. Since the second switching element is ON-controlled, it is possible to provide a switching power supply that can suppress the inrush current by the current limiting action of the resistor until the terminal voltage of the capacitor reaches a predetermined voltage. (C) Since the diode, the capacitor and the current limiting circuit are connected in series and both ends of the series connection circuit are connected in parallel to the first switching element, the second switching element is turned on. In the steady state after the switching, the current flowing in the second switching element is at least the value obtained by subtracting the current flowing in the first switching element from the current flowing in the inductor. It is possible to provide a highly efficient switching power supply with a small power loss of the switching device of No. 2. (D) In the case of a configuration in which the DC output voltage is obtained from both ends of the series connection circuit of the capacitor and the current limiting circuit, in the steady state, the current flowing through the second switching element is only the fluctuation due to the charge / discharge ripple of the capacitor. Therefore, the power loss of the second switching element is further reduced, and a highly efficient switching power supply 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 showing another embodiment of the switching power supply according to the present invention.

FIG. 3 is an electric circuit diagram showing a configuration of a specific example of a switching power supply according to the present invention.

FIG. 4 is an electric circuit diagram 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 target setting circuit.

FIG. 6 is an electric circuit diagram showing another embodiment 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 target setting circuit.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 rectifier circuit 11, 12 output terminal 2 booster circuit 21 switching element 22 inductor 23 diode 24 capacitor 25 current limiting circuit 3 control circuit 301 first input signal 302 second input signal 31 control signal 32 release signal Vr rectified output voltage Vo DC output voltage

Claims (4)

[Scope of utility model registration request] 1. A switching power supply having a rectifier circuit, a booster circuit, and a control circuit, wherein the rectifier circuit is a circuit that rectifies an AC power supply to obtain a rectified output, and the booster circuit is a first Switching element, an inductor, a diode, a capacitor, and a current limiting circuit, the first switching element is on / off driven at a frequency higher than the frequency of the AC power supply, and the inductor is The first switching element is connected in series, both ends of the series connection circuit are connected to the output terminal of the rectifier circuit, the current limiting circuit is composed of a parallel connection circuit of a resistor and a second switching element, -De,
A circuit in which the capacitor and the current limiting circuit are connected in series, both ends of the series connection circuit are connected in parallel to the first switching element, and the terminal voltage of the capacitor is used as a DC output voltage; The circuit is a switching power supply that is a circuit that turns on the second switching element at a timing when the terminal voltage becomes equal to or higher than a predetermined value. 2. The switching power supply according to claim 1, wherein the DC output voltage is obtained from both ends of a series connection circuit of the capacitor and the current limiting circuit. 3. The control circuit monitors the terminal voltage, and when the terminal voltage exceeds a predetermined value, the second circuit
The switching power supply according to claim 1, wherein the switching element is controlled to be turned on. 4. The switching power supply according to claim 1, wherein the control circuit turns on the second switching element with a predetermined delay time after the AC power supply is turned on.