JP2007288827A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply in which the power consumption of a backup power supply circuit can be reduced when an electronic apparatus is in standby (not operating). <P>SOLUTION: A secondary circuit 10b of a main power supply circuit 10 is provided with a rectifier circuit 31 for supplying a drive voltage to a PWM control section 173 which performs the switching control of a switching element 15. On the other hand, a primary circuit 10a of the main power supply circuit 10 is provided with a PWM control section 144 performing the switching control of the switching element 15 such that a DC voltage outptted to a load becomes lower than the drive voltage of the load and the DC voltage outputted from the rectifier circuit 31 to a PWM control section 174 has a drive voltage value at which the PWM control section 174 can operate when the PWM control section 173 does not perform the switching control of the switching element 15. The drive voltage to the PWM control section 144 is supplied from a backup power supply circuit 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply device used in an electronic device, and more particularly to a technique for reducing power consumption during standby of the electronic device.

Television broadcast receivers and video recorders convert DC voltage rectified and smoothed from AC voltage supplied from commercial AC power into desired DC voltage by controlling the duty ratio of switching pulse of switching circuit. There is a switching power supply that outputs to other electronic devices such as electrical appliances (see, for example, Patent Document 1).
On the other hand, in order to reduce the power consumption of electronic devices during standby, separately from the main power supply circuit that supplies power when the electronic devices are in operation, power is supplied to a control unit such as a microcomputer during standby (not in operation). A switching power supply device including a backup power supply circuit to perform is known.

Hereinafter, a conventional switching power supply Y having the backup power supply circuit will be described with reference to FIG.
As shown in FIG. 3, in the switching power supply device Y, an AC voltage supplied from input terminals a1 and a2 connected to a commercial AC power supply 1 is supplied to a main power supply circuit 10 via a filter circuit 2 such as a noise filter. (An example of a first power supply circuit) and a backup power supply circuit 20 (an example of a second power supply circuit). The output terminals b1 and b2 of the main power supply circuit 10 are connected to a load of an electronic device, and the output terminals c1 and c2 of the backup power supply circuit 20 are connected to a microcomputer (control unit) of the electronic device and its peripheral circuits. It is connected.
Although the supply of the AC voltage to the backup power supply circuit 20 is always performed, whether the AC voltage is supplied to the main power supply circuit 10 is provided between the filter circuit 2 and the main power supply circuit 10. It is controlled by turning ON / OFF the switch S1. Note that ON / OFF of the switch S1 is controlled by the microcomputer which functions by receiving power supply from the backup power supply circuit 20.

First, the configuration of the main power supply circuit 10 will be described.
The main power supply circuit 10 includes a primary circuit 10a connected to the commercial AC power supply, a secondary circuit 10b connected to the load, and a transformer that insulates the primary circuit 10a and the secondary circuit 10b. 11.
The primary side circuit 10a includes a rectifier circuit 12 (an example of a first rectifier circuit), a PFC circuit 13 (an example of stabilization means), a PWM control circuit 14 and a switching element 15 (an example of a first switching circuit). The secondary circuit 10b is provided with a rectifier circuit 16 (an example of a second rectifier circuit) and a PWM control circuit 17.
The rectifier circuit 12 includes a rectifier element 121, a coil 122, and a capacitor 123. An AC voltage supplied from the input terminals a1 and a2 connected to the commercial AC power source through the filter circuit 2 is DC voltage is output after rectification and smoothing. The DC voltage output from the rectifier circuit 12 is input to the PFC circuit 13.

The PFC circuit 13 includes a reactor 131, a diode 132, a switching element 133 (an example of a second switching circuit), and a capacitor 134. When the switching element 133 is controlled by the PWM control circuit 14, By performing a switching operation of the DC voltage input from the rectifier circuit 12, the DC voltage is stabilized and output. As the switching element 133, for example, an FET or a transistor is used.
The PWM control circuit 14 includes an input current detection circuit 141 that detects a current input to the PFC circuit 13, an output current detection circuit 142 that detects a current output from the PFC circuit 13, and the PFC circuit 13. A voltage detection circuit 143 that detects the output voltage, an ASIC that performs PWM control of the switching element 133 based on values detected by the input current detection circuit 141, the output current detection circuit 142, and the voltage detection circuit 143. And a PWM control unit 144. Supply of power to the PWM control unit 144 is performed by a rectifier circuit 23 described later provided in the backup power supply circuit 20.

The DC voltage output from the PFC circuit 13 is converted into an AC voltage by the switching operation of the switching element 15 controlled by the PWM control circuit 17 and input to the primary winding 11 a of the transformer 11. For the switching element 15, for example, an FET or a transistor is used.
The PWM control circuit 17 includes an output current detection circuit 171 that detects a current output from the rectifier circuit 16, a voltage detection circuit 172 that detects a voltage output from the rectifier circuit 16, and the output current detection circuit 171. And a PWM control unit 173 (an example of a first switching control unit) such as an ASIC that performs PWM control of the switching element 15 based on a detection value by the voltage detection circuit 172, and a voltage supplied to the PWM control unit 173 Starts the PWM control unit 173 when the operating voltage of the PWM control unit 173 is reached, and a drive circuit that drives the switching element 15 in accordance with a control signal transmitted from the PWM control unit 173 175 and a photocoupler 176 that electrically insulates the PWM controller 173 and the drive circuit 174 from each other. , The has. Supply of power to the PWM control unit 173 is performed by a rectifier circuit 27 described later provided in the backup power supply circuit 20.

When an AC voltage is applied to the primary winding 11 a of the transformer 11 by PWM control of the switching element 15 by the PWM control circuit 17, an AC voltage is induced in the secondary winding 11 b of the transformer 11. The AC voltage output from the secondary winding 11 b of the transformer 11 is input to the rectifier circuit 16.
The rectifier circuit 16 includes diodes 161, 162, a coil 163, and a capacitor 164, and rectifies and smoothes the AC voltage input from the transformer 11 to output a DC voltage. The DC voltage output from the rectifier circuit 16 is supplied to the load of the electronic device via the output terminals b1 and b2.

Next, the configuration of the backup power supply circuit 20 will be described.
The backup power circuit 20 includes a primary circuit 20a connected to the commercial AC power supply, a secondary circuit 20b connected to the microcomputer and its peripheral circuits, the primary circuit 20a, and the secondary circuit. And a transformer 21 that insulates 20b.
The primary side circuit 20a is provided with rectifier circuits 22 and 23 (an example of a fourth rectifier circuit), a switching element 24 and a PWM control circuit 25, and the secondary side circuit 20b includes a rectifier circuit 26, 27 is provided.

The rectifier circuit 22 includes a rectifier element 221 and a capacitor 222, and rectifies and smoothes an AC voltage supplied via the filter circuit 2 from the input terminals a1 and a2 connected to the commercial AC power source. To output DC voltage.
The DC voltage output from the rectifier circuit 22 is converted into an AC voltage by the switching operation of the switching element 24 controlled by the PWM control circuit 25 and input to the primary winding 21 a of the transformer 21. For the switching element 24, for example, an FET or a transistor is used.
The PWM control circuit 25 includes a voltage detection circuit 251 that detects a voltage output from the rectifier circuit 26, and a PWM control such as an ASIC that performs PWM control of the switching element 24 based on a detection value by the voltage detection circuit 251. 252; a drive circuit 253 that drives the switching element 24 according to a control signal transmitted from the PWM controller 252; and a photocoupler 254 that electrically insulates the voltage detector 251 and the PWM controller 252. And have.

When an AC voltage is applied to the primary winding 21a of the transformer 21 by PWM control of the switching element 24 by the PWM control circuit 25, the transformer 21 includes a secondary first winding 21b, a secondary second winding 21c, An AC voltage is induced in each secondary third winding 21d.
The AC voltage output from the secondary first winding 21b of the transformer 21 is output to the rectifier circuit 26, the AC voltage output from the secondary second winding 21c is output to the rectifier circuit 23, and the secondary third winding 21d. The alternating voltage is input to the rectifier circuit 27.
The rectifier circuit 26 includes a diode 261 and a capacitor 262, and rectifies and smoothes the AC voltage input from the transformer 21 to output a DC voltage. The DC voltage output from the rectifier circuit 26 is supplied to the microcomputer of the electronic device and its peripheral circuits through the output terminals c1 and c2.
The rectifier circuit 23 includes a diode 231, a capacitor 232, and a stabilization circuit 233, and rectifies and smoothes the AC voltage input from the transformer 21 to output a DC voltage. The DC voltage output from the rectifier circuit 23 is supplied as a power source for the PWM controller 144.
The rectifier circuit 27 includes a diode 271, a capacitor 272, and a stabilization circuit 273, and rectifies and smoothes the AC voltage input from the transformer 21 to output a DC voltage. The DC voltage output from the rectifier circuit 27 is supplied as a power source for the PWM controller 173.

In the switching power supply device Y configured in this way, even when the switch S1 is in an OFF state, that is, in a standby state where the load of the electronic device is not operating, the backup power supply circuit 20 causes the microcomputer and its peripheral circuits, etc. The power supply to the PWM control unit 144 and the PWM control unit 173 is always performed. Therefore, the switching power supply Y consumes power in the backup power supply circuit 20 even in a standby state.
When an operation such as an operation start request is performed by the user, the switch S1 is switched from OFF to ON according to a power supply start instruction from the microcomputer, and control by the PWM control units 144 and 173 is started. . As a result, the AC voltage supplied from the commercial AC power source 1 is converted into a DC voltage via the rectifier circuit 12, the PFC circuit 13, the switching element 15, the transformer 11, and the rectifier circuit 16, and then the The output terminals b1 and b2 are supplied.
Japanese Patent Laid-Open No. 2002-218749

Generally, reduction of power consumption during standby is strongly desired in various electronic devices. For this reason, it is desirable that the circuit configuration of the backup power supply circuit 20 that is operated even during standby and consumes power is reduced as much as possible, and the number of windings of the transformer 21 is reduced.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching power supply device capable of reducing the power consumption of the backup power supply circuit when the electronic device is on standby (when not operating). Is to provide.

In order to achieve the above object, the present invention provides a first insulating means for electrically insulating the AC power supply and the load from an AC power supply to a load of the switching power supply device in response to a predetermined power supply start instruction. The AC power supply and the control means are electrically connected from the AC power supply to the control means of the switching power supply device regardless of the presence or absence of the predetermined power supply start instruction. And a second power supply circuit that supplies power via a second insulating means that insulates the first power supply circuit from the AC power supply. A first rectifier circuit for converting the output AC voltage into a DC voltage; and a first rectifier for converting the DC voltage output from the first rectifier circuit into an AC voltage and outputting the AC voltage to the first insulating means. Switch A second rectifier circuit that converts the AC voltage output from the first insulating means into a DC voltage and outputs the DC voltage to the load, and a DC voltage output from the second rectifier circuit to the load. The first switching control means for controlling the switching of the first switching circuit so that the driving voltage value of the load becomes the load voltage, and the alternating voltage output from the first insulating means is converted into a direct current voltage to A third rectifier circuit that outputs to the first switching control means and a primary side of the first insulating means are provided, and the first switching control means performs switching control of the first switching circuit. If the DC voltage output from the second rectifier circuit to the load is lower than the drive voltage value of the load and the third rectifier circuit supplies the first switching control And a second switching control means for controlling the switching of the first switching circuit so that the DC voltage outputted to the first switching control means becomes a drive voltage value operable by the first switching control means. The second power supply circuit is provided on the primary side of the second insulating means, and converts the AC voltage output from the AC power supply into a DC voltage that is an operating voltage value of the second switching control means. The switching power supply device is characterized by having a fourth rectifier circuit that outputs to the second switching control means. Here, the first switching control means and the second switching control means, for example, perform PWM control of the first switching circuit.
In the switching power supply device configured as described above, since the third rectifier circuit that has been conventionally provided on the second power supply circuit side is provided on the first power supply circuit side, the second power supply circuit side is provided. The configuration of the power supply circuit can be simplified as compared with the prior art, and the number of windings of the second insulating means such as a transformer provided in the second power supply circuit can be reduced. Therefore, power consumption in the standby state of the switching power supply device driven only by the second power supply circuit can be reduced.

Also, a second switching circuit that performs a switching operation of the DC voltage output from the first rectifier circuit is provided, and the second switching circuit is controlled by the second switching control means. It is conceivable to implement a stabilizing function for stabilizing the DC voltage output from the first rectifier circuit. That is, it can be considered that the second switching control means is configured to be used for both the stabilization function and the function of switching control of the first switching circuit.
As a specific configuration example of the present invention, the second switching control means includes a first signal path continuing from the first switching control means to the first switching circuit, and the second switching control means. It is conceivable that the second signal path continuing from the first switching circuit to the first switching circuit is switched depending on whether or not the first switching control means is driven. More specifically, it is configured to detect the presence or absence of a control signal on the first signal path and switch between the first signal transmission path and the second signal transmission path according to the detection result. .

  According to the present invention, since the third rectifier circuit conventionally provided on the second power supply circuit side is provided on the first power supply circuit side, the configuration of the second power supply circuit is conventionally In addition, the configuration can be simplified, and the number of windings of the second insulating means such as a transformer provided in the second power supply circuit can be reduced. Therefore, power consumption in the standby state of the switching power supply device driven only by the second power supply circuit can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of the switching power supply device X according to the embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of the switching power supply device X when the main power supply is activated. In addition, the same code | symbol is attached | subjected to the component similar to the said conventional switching power supply apparatus Y (refer FIG. 3), and the description is abbreviate | omitted.
As shown in FIG. 1, the switching power supply device X according to the embodiment of the present invention is replaced with the rectifier circuit 27 (see FIG. 3) provided in the backup power supply circuit 20 of the conventional switching power supply device Y. A rectifier circuit 31 (an example of a third rectifier circuit) connected to the secondary second winding 11c of the transformer 11 of the main power supply circuit 10 is provided.
In the switching power supply device X configured as described above, when an AC voltage is applied to the primary winding 11a of the transformer 11, the AC voltage induced in the secondary second winding 11c of the transformer 11 is converted into the rectification. After being rectified and smoothed by the circuit 31 and converted into a DC voltage, it is supplied as a power source for the PWM controller 173.

In addition to the PWM control function of the switching element 133, the PWM control unit 144 provided in the switching power supply device X outputs a predetermined switching control signal to the drive circuit 175 that drives the switching element 15. It has a function to do. As described above, the PWM control unit 144 is always supplied with drive power from the rectifier circuit 23 of the backup power supply circuit 20.
Here, the switching control signal output from the PWM control unit 144 to the drive circuit 175 is such that the DC voltage output from the rectifier circuit 16 is lower than the drive voltage that can drive the load of the electronic device. The DC voltage output from the rectifier circuit 31 is set in advance so as to be a drive voltage at which the PWM controller 173 can operate.

Further, the switching power supply device X includes an output state detection circuit 32 that detects whether or not a switching control signal is output from the PWM control unit 173, and the PWM control unit 144 according to a detection result by the output state detection circuit 32. And a signal path switching circuit 33 (an example of a signal path switching means) that switches a signal path so as to transmit a switching control signal output from any one of the PWM control unit 173 to the drive circuit 175. .
When the output state detection circuit 32 detects that the switching control signal is output from the PWM control unit 173, the signal path switching circuit 33 outputs the switching control signal output from the PWM control unit 173. Is transmitted to the drive circuit 175, and when the output state detection circuit 32 detects that the switching control signal is not output from the PWM control unit 173, the switching output from the PWM control unit 144 is performed. A control signal is transmitted to the driving circuit 175.

In the switching power supply device X configured as described above, the circuit configuration of the secondary side circuit 20b of the backup power supply circuit 20 is simplified compared to the conventional switching power supply device Y. The number of lines can be reduced, and standby power consumed in the backup power supply circuit 20 during standby is reduced.
The operation of the switching power supply device X will be described below with reference to FIG. 1 and according to the timing chart of FIG. 2A is a state of the switch S1, FIG. 2B is a switching control signal input from the PWM control unit 144 to the signal path switching circuit 33, and FIG. 2C is the PWM control. FIG. 2D shows the switching control signal output from the signal path switching circuit 33, and FIG. 2E shows the output terminals b1 and b2. 2 (f) is a DC voltage output from the rectifier circuit 31, FIG. 2 (g) is a DC voltage output from the stabilization circuit 32, and FIG. 2 (h) is the starter circuit. The control signal output from 174 is shown.

First, when a power supply start instruction from the microcomputer is input to the switch S1, the PWM control unit 144, and the PWM control unit 173, the switch S1 is switched from OFF to ON, and the PWM control unit 144 is Driven (at time T1 in FIG. 2).
At this time (T1), since the drive power is not supplied to the PWM control unit 173, the PWM control unit 173 is not driven. Accordingly, since the output state detection circuit 32 does not detect the output of the switching control signal from the PWM control unit 173, the signal path switching circuit 33 causes the signal path (from the PWM control unit 144 to the drive circuit 175) ( An example of the second signal path) has been established. Therefore, the switching control signal (FIG. 2B) output from the PWM controller 144 is input to the drive circuit 175 (FIG. 2D).

When a switching control signal (FIG. 2B) output from the PWM controller 144 is input to the drive circuit 175, the switching operation of the switching element 15 is performed by the drive circuit 175, and the transformer 11 AC voltage is supplied to the primary winding 11a.
As a result, the AC voltage induced in the secondary winding 11 b of the transformer 11 is input to the rectifier circuit 16. At this time, the rectifier circuit 16 outputs a DC voltage Vm0 obtained by rectifying and smoothing the AC voltage (FIG. 2 (e)).
The AC voltage induced in the secondary second winding 11 c of the transformer 11 is input to the rectifier circuit 31. At this time, the rectifier circuit 31 outputs a DC voltage Vs0 obtained by rectifying and smoothing the AC power supply (FIG. 2 (f)).
Here, the DC voltage Vm0 is lower than the drivable voltage that can drive the load of the electronic device, and the DC voltage Vs0 is equal to or higher than the drivable voltage that the PWM control unit 173 can drive.

The DC voltage Vs0 output from the rectifier circuit 31 is stabilized by the stabilizing circuit 32 to a driveable voltage Vi that allows the PWM control unit 173 to be driven, and then supplied to the PWM control unit 173 ( FIG. 2 (g)).
As a result, since the start circuit 174 detects that the supply voltage value to the PWM control unit 173 has reached the drive voltage value Vi, a drive start signal is transmitted from the start circuit 174 to the PWM control unit 173. (FIG. 2 (h)), the drive of the PWM controller 173 starts (at time T2 in FIG. 2).
Then, after the drive of the PWM control unit 173 is started and various start-up processes in the PWM control unit 173 are finished, the switching control to the signal path switching circuit 33 by the PWM control unit 173 from the time T3 shown in the figure. Signal transmission is started (FIG. 2C).

At this time, since the signal detection circuit 32 detects the transmission of the switching control signal from the PWM control unit 173, the signal path switching circuit 33 causes the signal path continuing from the PWM control unit 173 to the drive circuit 175. (An example of a first signal path) is established. That is, the signal path switching circuit 3 switches the signal path from the PWM control unit 144 to the drive circuit 175 and the signal path from the PWM control unit 173 to the drive circuit 175. Therefore, the switching control signal (FIG. 2C) output from the PWM control unit 173 is transmitted to the drive circuit 173 (FIG. 2D).
Here, the PWM control unit 173 functions so that the switching control signal generated by the PWM control unit 173 matches the voltage across the output terminals b1 and b2 with a preset DC voltage Vm1.
Therefore, the AC voltage input from the transformer 11 to the rectifier circuit 16 and the rectifier circuit 31 increases, and the DC voltage Vm1 is output from the rectifier circuit 16 (FIG. 2E). DC voltage Vs1 is output (FIG. 2 (f)).
Here, the DC voltage Vm1 is a drive voltage of the load of the electronic device, and the DC voltage Vs1 is equal to or higher than the drive voltage Vi of the PWM control unit 173. However, the DC voltage supplied from the rectifier circuit 31 to the PWM controller 173 is adjusted to the drive voltage Vi of the PWM controller 173 by the stabilizing circuit 32 (FIG. 2 (g)).
Thereafter, the DC voltage supplied to the load of the electronic device is PWM-controlled by the PWM control unit 173 according to the driving state of the load.

As described above, in the switching power supply device X, when the switching control of the switching element 15 is not performed by the PWM control unit 173 by the PWM control unit 144 and the signal path switching circuit 33, The DC voltage output from the rectifier circuit 16 to the load is lower than the drive voltage value of the load, and the DC voltage output from the rectifier circuit 31 to the PWM controller 173 is operable by the PWM controller 173. Switching control of the switching element 15 is performed so that the driving voltage value is obtained. The PWM controller 144 and the signal path switching circuit 33 when performing such control correspond to second PWM control means.
In the switching power supply device X that can be started in this way, as described above, the rectifier circuit 31 that is a power supply circuit for driving the PWM control unit 173 is provided on the main power supply circuit 10 side. Therefore, the configuration of the backup power supply circuit 20 can be simplified as compared with the prior art, and the number of windings of the transformer 21 of the backup power supply circuit 20 can be reduced. Thereby, in the switching power supply device X, power consumption can be reduced when the electronic device is not driven (standby), that is, when only the backup power supply circuit 20 is driven.

1 is a block diagram showing a schematic configuration of a switching power supply device according to an embodiment of the present invention. The figure for demonstrating the operation | movement at the time of the main power supply starting in the switching power supply which concerns on embodiment of this invention. The block diagram which shows schematic structure of the conventional switching power supply device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Filter circuit 10 ... Main power supply circuit (an example of a first power supply circuit)
10a ... Primary circuit 10b ... Secondary circuit 11 ... Transformer (an example of first insulating means)
12 ... Rectifier circuit (an example of a first rectifier circuit)
13 ... PFC circuit 14 ... PWM control circuit (an example of second switching control means)
15 ... Switching element 16 ... Rectifier circuit (an example of a second rectifier circuit)
17 ... PWM control circuit (an example of first switching control means)
20 ... Backup power supply circuit (an example of a second power supply circuit)
20a ... Primary side circuit 20b ... Secondary side circuit 21 ... Transformer (an example of second insulating means)
22, 23 ... Rectifier circuit 24 ... Switching element 25 ... PWM control circuit 26 ... Rectifier circuit 31 ... Rectifier circuit (an example of a third rectifier circuit)

Claims (5)

A first power supply circuit that supplies power from an AC power supply to a load of the switching power supply device according to a predetermined power supply start instruction via first insulating means that electrically insulates the AC power supply from the load When,
Regardless of the presence or absence of the predetermined power supply start instruction, electric power is supplied from the AC power supply to the control means of the switching power supply device via the second insulating means for electrically insulating the AC power supply and the control means. A second power supply circuit to supply;
A switching power supply device comprising:
The first power circuit is
A first rectifier circuit that converts an AC voltage output from the AC power source into a DC voltage, and a DC voltage output from the first rectifier circuit is converted into an AC voltage and output to the first insulating means. A first switching circuit for converting the AC voltage output from the first insulating means into a DC voltage and outputting the DC voltage to the load; and from the second rectifier circuit to the load. A first switching control means for controlling the switching of the first switching circuit so that the output DC voltage becomes a drive voltage value of the load; and the AC voltage output from the first insulating means is a DC voltage. A third rectifier circuit that converts the output to the first switching control means and a primary side of the first insulating means, and the first switching circuit is provided by the first switching control means. When the switching control is not performed, the DC voltage output from the second rectifier circuit to the load is lower than the drive voltage value of the load, and the first rectifier circuit supplies the first switching Second switching control means for performing switching control of the first switching circuit so that a DC voltage output to the control means becomes a drive voltage value at which the first switching control means can operate. Become,
The second power circuit is
Provided on the primary side of the second insulating means, and converts the AC voltage output from the AC power source into a DC voltage that is equal to or higher than the drive voltage value of the second switching control means, to the second switching control means. A switching power supply comprising a fourth rectifier circuit for output.   The switching power supply device according to claim 1, wherein the first switching control means and / or the second switching control means performs PWM control of the first switching circuit. A second switching circuit that performs a switching operation of the DC voltage output by the first rectifier circuit;
3. The stabilizing means for stabilizing the DC voltage output from the first rectifier circuit by the second switching control means performing switching control of the second switching circuit. The switching power supply device according to any one of the above.   The second switching control means has a first signal path from the first switching control means to the first switching circuit, and a second signal path from the second switching control means to the first switching circuit. 4. The switching power supply device according to claim 1, further comprising: a signal path switching unit that switches the signal path according to whether or not the first switching control unit is driven. 5. Further comprising signal presence / absence detecting means for detecting presence / absence of a control signal on the first signal path,
5. The switching power supply device according to claim 4, wherein the signal path switching means switches between the first signal transmission path and the second signal transmission path according to a detection result by the signal presence / absence detection means.

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