JP2010263713A - Switching power supply device, ac power supply device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply device achieving a configuration at low cost, where heating values of integrated circuits do not exceed tolerance heat quantities of packages. <P>SOLUTION: The switching power supply device 50 includes: the integrated circuit 20 incorporating a PCHFET 12 driven by PWM_H and an NCHFET 11 driven by PWM_L; and a filter connected to an output terminal of the integrated circuit 20 and composed of a coil 15 and a capacitor 16. The switching power supply device 50 includes a diode 13 for connecting anode and cathode terminals to the GND and PWMO, respectively, and a diode 14 for connecting anode and cathode terminals to the output terminal and VCC, respectively, outside the integrated circuit 20, a period when both of the PCHFET 12 and NCHFET 11 are turned off is provided, and one of the diodes 13, 14 is turned on during the period, thus suppressing heat generation in the integrated circuit 20. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a switching power supply device, and more particularly to a circuit configuration of an integrated circuit when a switching power supply is integrated.

  With the progress of global warming phenomenon, energy saving is an issue in every situation. Especially in the power supply field, energy-saving power sources are common sense. That is, the importance of a highly efficient conversion method is very high, and many efficient conversion methods are used in switching power supplies. In other words, the switching power supply is a highly efficient conversion method compared to the dropper power supply or shunt power supply. However, in order to further increase the efficiency, the through-current prevention (dead time) by simultaneous switching of the high side and low side of the driver FET is possible. It is a well-known method to increase efficiency by performing

FIG. 13 is a configuration diagram relating to a driver unit and a filter when a driver FET is built in an integrated circuit in a conventional switching power supply. In FIG. 13, PCHFET 112 and NCHFET 111 which are driver FETs are a high-side driver and a low-side driver, respectively, and are driven by pulse width modulation signals PWM_H and PWM_L. PWMO is the output terminal of the integrated circuit 118 and is connected to the coil 115 of the filter.
The filter coil 115 and the capacitor 116 are arranged on the power supply board, and the output OUT of the filter is supplied to the load 117. Of course, the cutoff frequency of the filter is set to be lower than the frequency of the PWM signal. FIG. 2 shows a voltage characteristic of the output OUT with respect to a general PWM signal. The output voltage increases in proportion to the duty ratio (high period / (high period + low period)) of the PWM signal. Normally, a part of the output voltage is fed back, and the output voltage is controlled by comparing with a set value.

The operation of the switching power supply of FIG. 13 will be described with reference to FIGS. Normally, when the drive signals for the high side driver and the low side driver are made common, the high side driver and the low side driver are simultaneously turned on as shown in FIG. 14 at the moment when the drive signal is at an intermediate potential between the power supply and GND. A current 119 flows. In order to prevent such a through current 118, in general, a high-side driver drive signal and a low-side driver drive signal are provided separately, and the respective switching timings are slightly shifted to prevent the drivers from being simultaneously turned on. The dead time method is used.
FIG. 15 shows the timing. In FIG. 15, (1) is a period in which the PCHFET 112 is on, (2) is a period in which the NCHFET 111 is on, and the other period is a dead time.

In FIG. 16, changes in voltage, current, and power consumption at each timing in the switching power supply will be described. First, in a state before the period a, the PCHFET 112 is turned on, a current flows from the PCHFET to the capacitor 116, and the PCHFET consumes power. The direction of the current is positive in the direction of the arrow in FIG. When PWM_H becomes high during the period a, the PCHFET is turned off, and the potential of PWMO transits to GND or lower due to the back electromotive force of the inductance characteristics of the coil 115 in FIG.
At that time, when the potential of PWMO becomes lower than the threshold voltage of NCHFET 111 with respect to GND, NCHFET 111 becomes conductive, and a current flows from GND to PWMO (coil 115) (period a). During the period a, the current flowing through the NCHFET 111 and the back electromotive force of the coil 115 gradually decrease. Next, when PWM_L is set to high and the dead time ends, the ON resistance of the NCHFET 111 decreases (period b). During the period b, the PWMO potential becomes higher than GND, and the current flowing through the NCHFET 111 becomes a positive value.

Next, when PWM_L is set to low and the NCHFET 111 is turned off, the potential of PWMO is now higher than the power supply VCC due to the counter electromotive force of the coil 115. When the potential of the PWMO becomes higher than the threshold voltage of the PCHFET 112 with respect to the power supply VCC, the PCHFET 112 becomes conductive, and a current flows from the PWMO (coil 115) to the power supply VCC (period c). During the period c, the current flowing through the PCHFET 112 and the back electromotive force of the coil 115 gradually decrease. Next, PWM_H is set to low to end the dead time, and the on-resistance of the PCHFET 112 decreases (period d). During the period d, the PWMO potential becomes lower than the power supply VCC, and the current flowing through the PCHFET 112 becomes a positive value. The above operation is repeated.
The change in power consumed by the driver FET is shown at the bottom of FIG. When it is assumed that there is no through current 118, the power consumption becomes the largest during the period in which the on-resistance of the driver is increased, such as period a and period c. In general, it is required to shorten this period as much as possible and prevent a through current to suppress the power consumption as a whole.
Patent Document 1 discloses a method for improving the efficiency of the entire power supply by optimally adjusting the dead time.

As in Patent Document 1, it is possible to increase the efficiency of the entire power supply by adjusting the time (dead time) during which both the high-side FET and the low-side FET are turned off. When a power adjustment system is required and a plurality of power supplies are required, there is a problem that the overall cost increases.
In general, the switching power supply uses a power MOSFET as a driver, and when supplying a large amount of power, the driver FET often uses a single component. However, depending on the application or in a power supply with relatively low power consumption, the driver FET may be built in the control integrated circuit. For example, in the case of a tandem machine such as a high-voltage power supply for an image forming process (charging, development, transfer) in the image forming apparatus, a power supply for four colors is required, and even if the power supply amount per one is small. Many different power sources may be required. In such a case, if a single component power MOSFET is used, the number of components increases and the component arrangement becomes complicated. Therefore, it is useful to integrate the driver FET with the integrated circuit for power supply control.

However, when a plurality of driver FETs are built in, or even if only one driver FET is provided, the amount of heat generated by the on-resistance of the driver FET may exceed the allowable heat amount of the integrated circuit package. For example, when the package thermal resistance value is 55 ° C./W, the allowable heat quantity of the package is guaranteed up to an operation at an atmospheric temperature of 70 degrees, and if the operation is guaranteed up to a semiconductor junction temperature of 125 degrees, the allowable heat quantity of the package is (125−70) / 55 = 1W to 1W at maximum.
When this allowable heat amount is exceeded, it is difficult to guarantee the operation as an integrated circuit, and therefore some heat dissipation measures are usually taken. For example, it is possible to use a ceramic package with high heat dissipation characteristics or to dispose a heat dissipation FIN, but in any case, the cost increases.
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a switching power supply that realizes a low-cost configuration in which the amount of heat generated by the integrated circuit does not exceed the allowable amount of heat of the package of the integrated circuit when the driver FET is incorporated in the integrated circuit. An object is to provide an apparatus.

  To solve this problem, the present invention provides a switching power supply integrated circuit including a high-side switch element driven by a first PWM signal and a low-side switch element driven by a second PWM signal. A switching power supply device comprising: a filter connected to an output terminal of the switching power supply integrated circuit; and a filter constituted by an inductor element and a capacitive element, wherein an anode terminal is connected to the ground and a cathode terminal is connected to the output terminal. 1 diode, and a second diode having an anode terminal connected to the output terminal and a cathode terminal connected to a power source, provided outside the switching power supply integrated circuit, wherein the high-side switch element and the low-side switch element are both An off period is provided, and during the period, the first diode Is by conducting one of said second diode, characterized by being configured to suppress heat generation of the switching power supply integrated circuit.

According to a second aspect of the present invention, the switching power supply integrated circuit compares the set voltage with the output voltage of the filter or a proportional voltage of the output voltage, and integrates a difference between the voltages. A differential integrator that generates a control voltage to be compared with the triangular wave, a comparator that compares the control voltage with the triangular wave to generate a third PWM signal, and a third PWM signal generated by the comparator. And a PWM generator for generating the first PWM signal and the second PWM signal whose switching timings are shifted from each other, and the output voltage is controlled in accordance with the set voltage.
According to a third aspect of the present invention, in the multi-output switching power supply device including a plurality of the output terminals, the high-side switch element and the low-side switch element are provided in the respective output terminals, and the first diode and the second diode are provided. Each of the output terminals is provided.

A fourth aspect of the present invention relates to an AC power source device that generates an AC power source, comprising the switching power source device according to claim 2 or 3 and a transformer, wherein a sinusoidal voltage is input as the set voltage, and the output voltage An AC power supply is generated by comparing the output of the transformer or the proportional voltage of the output of the transformer with the set voltage.
According to a fifth aspect of the present invention, in the image forming apparatus according to the electrophotographic system, the AC power supply unit according to the fourth aspect is used as a charging power source for charging a uniform charge to the image carrier.
6. An image forming apparatus comprising a plurality of image carriers, wherein the switching power supply integrated circuit comprises a plurality of AC power supply devices according to claim 4 as a charging power source for charging the image carrier with a uniform charge. Is a single integrated circuit having a plurality of output terminals.

According to the present invention, in a switching power supply integrated circuit with a built-in driver FET, a diode is connected to the output terminal, and the driver FET causes a return current to flow to an external diode during the off period, thereby reducing the amount of heat generated in the integrated circuit. It becomes possible.
Further, by adopting the heat generation reduction method for the switching power supply integrated circuit according to the present invention for the feedback control power supply, the heat generation amount of the feedback control power supply can be reduced.
Further, even in the case of a multi-output power supply, it is effective for reducing the amount of heat generated by the switching power supply integrated circuit.
Further, even in the case of a high voltage power source, it is effective in reducing the heat generation amount of the integrated circuit.
Further, by employing the integrated circuit of the present invention in the charging device inside the image forming apparatus, it is possible to reduce the amount of heat generated in the integrated circuit.
Also, in the color image forming apparatus, the amount of heat generated in the integrated circuit can be reduced by employing the above-described integrated circuit as a high-voltage power supply for the charging device.

It is a block diagram regarding the driver part, filter, and diode of the switching power supply concerning the embodiment of the present invention. It is a figure showing the relationship between PWM duty and VCC. It is a figure which shows the waveform of each part of the switching power supply of this invention. It is a figure which shows the structure of the switching power supply using the structure of FIG. It is a figure which shows the structure of the triangular wave production | generation part in FIG. It is a figure which shows the block diagram of the difference integrator 23 in FIG. It is a figure which shows the dead time production | generation part in FIG. It is a figure which shows the structural example of a high voltage | pressure AC power supply. It is a figure which shows an example of a structure of the charging device which concerns on this invention. It is a perspective view which shows the external appearance of a charging roller. 2 is a diagram illustrating a configuration of an image forming unit of the image forming apparatus. FIG. It is a figure which shows the structure of the image formation part of a tandem type image forming apparatus. It is a block diagram regarding the driver part, filter, and diode of the switching power supply concerning the conventional embodiment. It is a figure which shows the mode of a through current. It is a figure which shows the timing relationship of a drive signal. It is a figure which shows the waveform of each part of the conventional switching power supply.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
FIG. 1 is a configuration diagram relating to a driver unit, a filter, and a diode of a switching power supply according to an embodiment of the present invention. The switching power supply 50 includes a switching circuit including a PCHFET (high side switch element) 12 driven by PWM_H (first PWM signal) and an NCHFET (low side switch element) 11 driven by PWM_L (second PWM signal). A switching power supply comprising a power supply integrated circuit (hereinafter simply referred to as an integrated circuit) 20 and a filter connected to an output terminal of the integrated circuit 20 and configured by a coil (inductor element) 15 and a capacitor (capacitance element) 16. In the device 50, a diode (first diode) 13 having an anode terminal connected to GND (ground) and a cathode terminal connected to PWMO (output terminal), and an anode terminal connected to an output terminal and a cathode terminal VCC (power supply). A diode (second diode) 14 connected to A period in which both the PCHFET 12 and the NCHFET 11 are turned off is provided outside the integrated circuit 20, and either the diode 13 or the diode 14 is made conductive during this period to suppress heat generation of the integrated circuit 20. .

That is, in FIG. 1, the driver FETs PCHFET 12 and NCHFET 11 are built in the integrated circuit 20. A signal for controlling on / off of the PCHFET 12 is PWM_H, and a signal for controlling on / off of the NCHFET 11 is PWM_L, both of which are pulse width modulation signals. PWMO is an output terminal of the integrated circuit 20 and is connected to the coil 15 of the filter. The filter coil 15 and the capacitor 16 are arranged on a power supply board. The diode 13 and the diode 14 are disposed outside the integrated circuit 20 and are used to flow a return current while both the PCHFET 12 and the NCHFET 11 are off. FIG. 2 shows a voltage characteristic of the output OUT with respect to a general PWM signal. The output voltage increases in proportion to the duty ratio (high period / (high period + low period)) of the PWM signal. Normally, a part of the output voltage is fed back, and the output voltage is controlled by comparing with a set value.
The operation of the switching power supply of FIG. 1 will be described with reference to FIG. FIG. 3 shows changes in voltage, current, and power consumption at each timing. First, in a state before the period a, the PCHFET 12 is turned on, a current flows from the PCHFET to the capacitor 16, and the PCHFET consumes power. The direction of the current is positive in the direction of the arrow in FIG. In the period a, when PWM_H becomes high, the PCHFET 12 is turned off, and the potential of PWMO transitions to GND or lower due to the counter electromotive force of the inductance characteristics of the coil 15 in FIG. At that time, when the potential of PWMO becomes lower than the ON voltage of the diode 13 with respect to GND (a voltage equal to or higher than the ON voltage is applied to both ends of the diode 13 in the positive direction), the diode 13 becomes conductive, and the PWMO (coil 15) A current flows through the photodiode 13 (period a).

Here, it is assumed that the threshold voltage of the NCHFET 11 is higher than the ON voltage of the diode 13. During the period a, the current flowing through the diode 13 and the back electromotive force of the coil 15 gradually decrease. Next, before the voltage applied to both ends of the diode 13 becomes smaller than the on-voltage of the diode 13, PWM_L is set to high to turn on the NCHFET 11 and make it conductive (period b). During the period b, the PWMO potential becomes higher than GND, and the current flowing through the NCHFET 11 becomes a positive value.
Next, when PWM_L is set to low and the NCHFET 11 is turned off, the potential of the PWMO is now higher than the power supply VCC due to the counter electromotive force of the coil 15. When the potential of PWMO becomes higher than the ON voltage of the diode 14 with respect to the power supply VCC, the diode 14 becomes conductive, and a current flows from the PWMO (coil 15) to the power supply VCC through the diode 14 (period c). Here, it is assumed that the threshold voltage of the PCHFET 12 is higher than the ON voltage of the diode 14. During the period c, the current flowing through the PCHFET 12 and the back electromotive force of the coil 15 gradually decrease.

Next, before the voltage applied to both ends of the diode 14 becomes smaller than the ON voltage of the diode 14, the PWM_H is set to low to turn on the PCHFET 12 and make it conductive (period d). During the period d, the PWMO potential becomes lower than the power supply VCC, and the current flowing through the PCHFET 12 becomes a positive value.
The above operation is repeated.
Compared with the case of FIG. 16, the power consumption consumed by the driver FET is consumed by the external diode 13 and the diode 14 during the period a, the period c, and the period e. It turns out that electric power becomes small. In particular, as the diode 13 and the diode 14, it is desirable to use a Schottky diode or the like that has a high operating speed, a low on-voltage, and a low on-resistance. As can also be seen from FIG. 3, the period in which both PCHFET 12 and NCHFET 11 are off, such as period a, period c, and period e, is as long as possible (within the period in which diode 13 and diode 14 are conducting). This is advantageous in terms of power consumption in the circuit 20.

FIG. 4 is a diagram showing a configuration of a switching power supply using the configuration of FIG. In FIG. 4, the integrated circuit 20 includes a triangular wave generation unit 21, a comparator 22, a difference integrator 23, a dead time generation unit 24, and a switching drive unit 25. Further, the outside of the integrated circuit 20 includes a diode 13, a diode 14, a coil 15, a capacitor 16, feedback resistance voltage divisions R 1 and R 2, and a load 17.
The difference between the input voltage and the FB voltage is integrated by the difference integrator 23 and output as a control signal. The control signal is compared with the triangular wave generated by the triangular wave generator 21 by the comparator 22 and converted to PWM. The PWM is input to the dead time generation unit 24, and a high side drive signal PWM_H and a low side drive signal PWM_L are generated. PWM_H and PWM_L are input to the switching drive unit 25, output as PWMO, and smoothed by a filter composed of the coil 15 and the capacitor 16 to generate an output OUT.
By feeding back the divided voltage of the output OUT as the FB voltage, the control system is configured as a whole, and an output voltage corresponding to the input voltage is generated. The switching drive unit 25 is configured by driver FETs such as the PCHFET 12 and the NCHFET 11 in FIG. In FIG. 4, the output OUT is divided as the FB voltage, but the output OUT may be directly used as the FB voltage.

FIG. 5 is a diagram showing the configuration of the triangular wave generator in FIG. In FIG. 5, the triangular wave generation unit 21 includes a current source I1, a Schmitt trigger circuit, a transistor, and a capacitor C1. The Schmitt trigger circuit is a circuit in which the threshold voltage changes depending on the transition direction of the input voltage, and the threshold is set to ref ± Vth, for example. For example, when TRIOUT exceeds ref + Vth, the output of the Schmitt trigger circuit is inverted and the transistor is turned on. The charge stored in C1 is discharged by the transistor, and TRIOUT is pulled down.
Here, when the potential of TRIOUT becomes lower than ref−Vth, the output of the Schmitt trigger circuit is inverted and the transistor is turned off. While the transistor is off, the capacitor C1 is charged by the current source I1. In this way, a sawtooth triangular wave is generated at TRIOUT.

FIG. 6 is a diagram showing the configuration of the difference integrator 23 in FIG. In FIG. 6, feedback is applied to the operational amplifier 23a, and the node n1 becomes the FB voltage due to a virtual short circuit. A current obtained by dividing the difference voltage between the input voltage and the FB voltage by the resistor R is stored in the capacitor C2, and an integrated output is generated.
FIG. 7 is a diagram showing the dead time generation unit in FIG. FIG. 7A shows a configuration for generating PWM_L and PWM_H from PWM, and FIG. 7B shows a timing chart. By adding capacity to node C, the node change of B is delayed from A, and the period is generated as a dead time. PWM_H has a longer high period than PWM_L.
FIG. 8 is a diagram illustrating a configuration example of a high-voltage AC power source. Although the switching power supply of FIG. 4 is basically used, the primary side of the transformer 34 is connected to the output OUT, and a high voltage is output from the secondary side. A sine wave is input as the input voltage. The high voltage AC output is divided and fed back as an FB voltage. By setting the turns ratio of the primary side and the secondary side of the transformer 34 to 1: n, a high-voltage AC output having an amplitude n times the amplitude of the input voltage applied to the primary side can be generated.

Moreover, it is preferable to apply the high-voltage AC power supply device according to the present invention to a charging device. An example of the configuration of the charging device 200 according to the present invention is shown in FIG. The charging device 200 includes a high voltage AC power supply device 1 and a charging roller 201. In the present embodiment, the photosensitive drum 210 is charged by a so-called proximity charging method, but the present invention is not limited to this.
For example, as shown in FIG. 10, the charging roller 201 includes a rod-shaped cored bar 202, a cylindrical elastic layer 203 provided so as to surround the cored bar 202, and a resistance set to a medium resistance, and an elastic layer 203. And a coating layer 204 that improves wear resistance and reduces foreign matter adhesion. A spacer 205 is provided so that a portion of the photosensitive drum 210 where no image is formed is not charged.
The spacer 205 may be provided not on the charging roller 201 but on the photosensitive drum 210. Further, a sheet-like member such as a belt may be disposed as a spacer between the charging roller 201 and the photosensitive drum 210. By applying the high-voltage AC power supply device 1 to the charging device 200 as described above, power saving of the charging device 200 can be realized.

Furthermore, it is preferable to apply the high-voltage AC power supply apparatus according to the present invention to an image forming apparatus as shown in FIG. The image forming apparatus 300 includes an AC charging device (charging device 200) that charges the photosensitive member at a high voltage, a DC charging device 302, an optical scanning device 303 that exposes image data, and an optical scanning device 303 around the photosensitive drum 301. A developing device 304 that attaches a charged toner to a recorded electrostatic latent image to visualize it, a transfer device 305 that transfers the toner attached to the photosensitive drum 301 to paper, and scrapes the toner remaining on the photosensitive drum 301. A cleaning device 306 or the like for stockpiling is provided.
Note that the configuration and operation of each unit are well known, and thus the description thereof is omitted. The image forming apparatus shown in FIG. 11 naturally includes a color image forming apparatus. By applying the charging device 200 having the high-voltage AC power supply device 1 to the image forming apparatus 300 as described above, power saving of the image forming apparatus 300 can be realized.

FIG. 12 shows a configuration diagram of a color image forming apparatus including a plurality of photosensitive drums. The color image forming apparatus 2000 is a tandem multicolor image forming apparatus that forms a full color image by superimposing four colors (black, cyan, magenta, and yellow). “Charging device K2, developing device K4, cleaning unit K5, and transfer device K6”, “photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6” for cyan, and magenta “Photosensitive drum M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6” and yellow “photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, and transfer device Y6” ”, An optical scanning device 2010, a transfer belt 2080, a fixing unit 2030, and the like. There.
Each photoconductor drum rotates in the direction of the arrow in FIG. 12, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photoconductor drum in the order of rotation. Each charging device uniformly charges the surface of the corresponding photosensitive drum.

The surface of each photoconductive drum charged by the charging device is irradiated with light by the optical scanning device 2010, and a latent image is formed on each photoconductive drum. Then, a toner image is formed on the surface of each photosensitive drum by a corresponding developing device. Further, the toner image of each color is transferred onto the recording paper by the corresponding transfer device, and finally the image is fixed on the recording paper by the fixing unit 2030.
The charging device of FIG. 9 is used as the charging devices K2, C2, M2, and Y2, and the configuration of FIG. 8 is used as the high-voltage AC power supply device, and the high-voltage AC power supply device for each color is integrated into one integrated circuit. This simplifies the configuration of the high-voltage power supply unit and enables downsizing.

  11 NCHFET, 12 PCHFET, 13 Diode, 14 Diode, 15 Coil, 16 Capacity, 17 Load, 20 Switching Power Supply Integrated Circuit, 21 Triangular Wave Generator, 22 Comparator, 23 Difference Integrator, 24 Dead Time Generator, 25 Switching Drive 50, switching power supply

JP 2005-094994 A

Claims (6)

A switching power supply integrated circuit including a high-side switch element driven by the first PWM signal and a low-side switch element driven by the second PWM signal; an inductor element connected to an output terminal of the switching power supply integrated circuit; In a switching power supply device comprising a filter constituted by a capacitive element,
A switching power supply integrated circuit comprising: a first diode having an anode terminal connected to ground and a cathode terminal connected to the output terminal; and a second diode having an anode terminal connected to the output terminal and a cathode terminal connected to a power source. Prepared outside
A period during which both the high-side switch element and the low-side switch element are turned off is provided, and during this period, either one of the first diode or the second diode is made conductive to generate heat in the switching power supply integrated circuit. A switching power supply device configured to suppress the above. The switching power supply integrated circuit includes a triangular wave generator that generates a triangular wave;
A differential integrator that generates a control voltage to be compared with the triangular wave by comparing a set voltage with an output voltage of the filter or a proportional voltage of the output voltage, and integrating a difference between the voltages;
A comparator that compares the control voltage with the triangular wave to generate a third PWM signal;
A PWM generator that generates the first PWM signal and the second PWM signal whose switching timings are shifted from each other based on the third PWM signal generated by the comparator;
The switching power supply according to claim 1, wherein the output voltage is controlled according to the set voltage. In a multi-output switching power supply device comprising a plurality of the output terminals,
The said high side switch element and the said low side switch element are provided in each said output terminal, The said 1st diode and the said 2nd diode are provided in each said output terminal, The Claim 1 or 2 characterized by the above-mentioned. Switching power supply. In an AC power supply that generates an AC power supply,
A switching power supply device according to claim 2 and a transformer, wherein a voltage of a sine wave shape is input as the set voltage, and the output of the transformer or the transformer when the output voltage is applied to the transformer. An AC power supply apparatus is characterized in that an AC power supply is generated by comparing a proportional voltage of the output of the output with the set voltage.   5. An image forming apparatus according to claim 4, wherein the AC power supply device according to claim 4 is used as a charging power source for charging a uniform charge on the image bearing member in an electrophotographic image forming apparatus.   5. An image forming apparatus comprising a plurality of image carriers, comprising a plurality of AC power supply devices according to claim 4 as a charging power source for charging a uniform charge to the image carrier, wherein the switching power supply integrated circuit has a plurality of outputs. An image forming apparatus comprising a single integrated circuit including a terminal.

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