JP2005229737A - Direct-current power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand the range of a variable voltage output in a direct-current power supply device that has one converter circuit and produces both variable voltage output and constant voltage output. <P>SOLUTION: The direct-current power supply device comprises: a direct-current power source 1; a transformer 2; a switching element 6; a first diode 7; a first smoothing capacitor 8; a first load 9 that is the load of variable voltage output; a second diode 10; a limiting element 11; a second smoothing capacitor 12; a second load 13 that is the load of constant voltage output; an error amplifier 14 that amplifies the difference between variable voltage output and a command value; a switching frequency controlling means 15; an oscillator 16; a pulse generating means 17; and a driving means 18 for the switching element 6. The range of variable voltage output can be expanded by the following measure: when the variable voltage output drops, the output frequency of the oscillator 16 is increased by the switching frequency controlling means 15 to prevent constant voltage output drop. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a DC power supply device that can simultaneously supply a variable voltage output and a constant voltage output.

  Conventionally, in a DC power supply device having a variable voltage output and a constant voltage output, a constant voltage output is ensured in the first-stage converter circuit, and the variable voltage output is further reduced from the first-stage converter circuit output to In general, output is performed by a second-stage converter circuit. However, this configuration requires two converter circuits, and the number of parts is large, so that the entire circuit is complicated and disadvantageous in terms of cost. Therefore, a circuit configuration has been conceived in which a variable voltage output and a constant voltage output are output by a single converter circuit.

  For example, a conventional DC power supply device capable of supplying a variable voltage output and a constant voltage output at the same time includes a multi-winding transformer composed of a set of switching elements and three windings (see, for example, Patent Document 1). There is.

  A conventional DC power supply device will be described below with reference to FIGS. 7 and 8 with reference to the drawings.

  First, the configuration will be described with reference to FIG. FIG. 7 shows a block diagram of a conventional DC power supply device described in Patent Document 1. In FIG. The DC power source 1 is a power supply source, and is connected in series with the first winding 3 and the switching element 6 of the multi-winding transformer 2 having three windings. The second winding 4 of the multi-winding transformer 2 is connected to the first diode 7, and the first smoothing capacitor 8 connected to the first diode 7 is connected in parallel to the first load 9. . The third winding 5 of the multi-winding transformer 2 is connected to the second diode 10, and the second smoothing capacitor 12 connected to the second diode 10 is connected in parallel to the second load 13. Is done. The error amplifier 14 amplifies the difference between the voltage of the first load 9 and the reference voltage 26, and the first duty ratio setting unit 27 and the second duty setting unit 28 set the ON period of the switching element 6. Is for. The selection switch 29 is for selecting the first duty ratio setting unit 27 and the second duty setting unit 28, and the driving means 18 is for driving the switching element 6.

  Next, the operation of the conventional DC power supply device configured as described above will be described. During feedback operation in which a predetermined voltage is applied to the first load 9, the selection switch 29 selects and operates the first duty ratio setting unit 27.

  At this time, the first duty ratio setting unit 27 drives the switching element 6 by sending a signal to the driving means 18 so that the voltage of the first load 9 matches the reference voltage 26 according to the output of the error amplifier 14. . That is, when the voltage of the first load 9 decreases, the ON period of the switching element 6 is expanded, and the energy stored in the multi-winding transformer 2 during the ON period increases, so that the switching element 6 becomes When the power is turned off, the electric power supplied through the first diode 7 increases, and the voltage of the first load 9 is increased. Conversely, when the voltage of the first load 9 rises, control is performed by shortening the ON period of the switching element 6.

If the ON period of the switching element 6 of the second duty ratio setting unit 28 is fixed in advance to be a value of 1/10 or less than that during feedback operation, the voltage of the first load 9 is reduced. This can be realized by switching the selection switch 29 to the second duty ratio setting unit 28. (Hereafter, fixed duty operation is assumed.)
On the other hand, with respect to the voltage of the second load 13, the second diode 10 is connected to the third winding 5 of the multi-winding transformer 2 in a direction in which the second diode 10 conducts during the ON period of the switching element 6. There is no current-current limiting element such as a reactor between the diode 10 and the second load 13. For this reason, the second smoothing capacitor 12 is charged in a time sufficiently shorter than the ON period determined by the second duty ratio setting unit 28, and the number of turns of the winding 3 and the winding 5 of the multi-winding transformer 2. A constant voltage according to the ratio can be obtained. Therefore, even when the voltage of the first load 9 is changed, the voltage of the second load 13 is not affected, and the variable voltage output and the constant voltage output can be realized by one converter.

FIG. 8 shows voltage waveforms of winding 4 and winding 5 of multi-winding transformer 2 during feedback operation and fixed duty operation. 8A shows the voltage waveform of the winding 4 during feedback operation, and FIG. 8B shows the voltage waveform of the winding 5 during feedback operation. (C) shows the voltage waveform of the winding 4 during fixed duty operation, and (d) shows the voltage waveform of the winding 5 during fixed duty operation. V1 represents the voltage of the first load 9, and V2 represents the voltage of the second load 12. ON and OFF indicate timings when the switching element 6 is in an on state and an off state, respectively.
JP-A-5-219739

  However, in the conventional configuration, since there is no element for limiting the current that flows when the switching element 6 is turned on on the second load 13 side that is a constant voltage output, the current that flows through the switching element cannot be limited. There were problems such as failure to protect the elements and increased noise and loss. Therefore, in practice, it is necessary to insert a current limiting element such as a resistor or a saturable reactor in order to limit the maximum value of the current that flows when the switching element is turned on.

  On the other hand, when the current limiting element as described above is inserted, in order to apply a constant voltage according to the turns ratio of the transformer to the second load, a minimum for charging the second smoothing capacitor is required. If the required time is determined and the ON period of the switching element is further shortened, it becomes impossible to maintain a constant voltage, so that the variable range of the voltage applied to the first load becomes narrow.

  The present invention solves the above-described conventional problems, and provides a DC power supply device that can widen the variable voltage range in a DC power supply device having both a variable voltage output and a constant voltage output in one converter circuit. The purpose is to do.

  In order to solve the above-described conventional problems, the DC power supply device of the present invention is configured to increase the frequency for driving the switching element when the variable voltage output command value is equal to or lower than the minimum voltage capable of maintaining the constant voltage output. It is a thing.

  As a result, the ON period of the switching element is further reduced. However, since the influence of increasing the number of times the smoothing capacitor on the constant voltage output side is charged is larger than that of the decrease, the variable voltage range can be expanded.

  The DC power supply device of the present invention can widen the variable voltage range in a DC power supply having both a variable voltage output and a constant voltage output with a single converter circuit.

  The first invention is a DC power supply, a multiwinding transformer having at least three windings, and a switching element connected in series with the first winding of the multiwinding transformer with respect to the DC power supply. And a first winding connected to the second winding of the multi-winding transformer and connected to discharge energy stored in the multi-winding transformer as a current when the switching element is in an off state. A diode, a first smoothing capacitor for smoothing the output of the first diode, a first load connected in parallel to the first smoothing capacitor, and the multi-winding when the switching element is on A second diode for rectifying the voltage generated in the third winding of the line transformer, a current limiting element for limiting a maximum value of a current flowing through the second diode, and a current flowing through the current limiting element A second smoothing capacitor to be smoothed, a second load connected in parallel to the second smoothing capacitor, a variable output voltage command for determining a voltage to be applied to the first load, and a voltage actually applied An error amplifier that amplifies the difference between the switching element, a switching frequency control unit that controls a switching frequency of the switching element in accordance with a value of a variable output voltage command, and an oscillator that changes its oscillation frequency according to the output of the switching frequency control unit, A pulse generating means for generating a pulse for driving the switching element by an output of the error amplifier and an output of the oscillator; and a driving means for driving the switching element in accordance with the output of the pulse generating means. As a result, the switching frequency is increased when the value of the variable output voltage command falls below the predetermined voltage. It is possible to prevent a reduction in the voltage applied to the second load Te, and a variable voltage output and the constant voltage output can be expanded a variable voltage range of the DC power supply apparatus that combines in one converter circuit.

  A second invention includes a DC power source, a transformer having two windings, a switching element connected in series with the first winding of the transformer with respect to the DC power source, and a first of the transformer A first diode connected to two windings and connected to discharge the energy stored in the transformer as a current when the switching element is in an off state, and smoothes the output of the first diode A first smoothing capacitor, a first load connected in parallel to the first smoothing capacitor, and a voltage generated in the second winding of the transformer when the switching element is in an on state are rectified. A second diode; a current limiting element for limiting a maximum value of a current flowing through the second diode; a second smoothing capacitor for smoothing a current flowing through the current limiting element; A second load connected in parallel to the smoothing capacitor, an error amplifier for amplifying a difference between a voltage applied to the first load and a variable output voltage command for determining a voltage applied to the first load, and a voltage actually applied, and a variable output Switching frequency control means for controlling the switching frequency of the switching element in accordance with the value of the voltage command, an oscillator whose oscillation frequency is changed by the output of the switching frequency control means, an output of the error amplifier, and an output of the oscillator Applied to the second load by providing pulse generation means for generating a pulse for driving the switching element and drive means for driving the switching element in accordance with an output of the pulse generation means It is possible to prevent voltage drop, and two transformer windings can be used to control variable voltage output and constant voltage output. DC power supply together can be realized both in over-capacitor circuit, it is possible to enlarge the variable voltage range.

  In the third invention, in particular, the switching frequency control means of the first or second invention is configured to control the switching frequency in accordance with the pulse width of the pulse generating means, so that the value of the variable output voltage command is set. The variable voltage range of the voltage applied to the first load can be expanded without using it, and when the voltage applied to the first load is used as an insulation output, the value of the variable output voltage command is insulated and transmitted. It is possible to omit the means to do.

According to a fourth aspect of the present invention, there is provided a DC power source, a reactor having a secondary winding, a switching element connected in series to the reactor with respect to the DC power source, and the switching element connected to the reactor and in an off state. Sometimes in parallel with the first diode connected to discharge the energy stored in the reactor as a current, a first smoothing capacitor for smoothing the output of the first diode, and the first smoothing capacitor A first load connected; a second diode for rectifying a voltage generated in a secondary winding of the reactor when the switching element is in an on state; and a maximum value of a current flowing through the second diode. A current limiting element for limiting, a second smoothing capacitor for smoothing the current flowing through the current limiting element, and the second smoothing capacitor. A second load connected to the first load, an error amplifier that amplifies a difference between a voltage that is actually applied and a variable output voltage command that determines a voltage to be applied to the first load, and a value of the variable output voltage command In response, switching frequency control means for controlling the switching frequency of the switching element, an oscillator whose oscillation frequency changes according to the output of the switching frequency control means, and the switching element driven by the output of the error amplifier and the output of the oscillator And a drive means for driving the switching element in accordance with the output of the pulse generation means, so that the voltage of the DC power supply is raised and lowered by a single converter circuit. It can have variable voltage output and constant voltage output that can be compressed, and expand its variable voltage range It is possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram of a DC power supply device according to a first embodiment of the present invention.

  In FIG. 1, a DC power source 1 is a power supply source and is connected in series with a first winding 3 and a switching element 6 of a multi-winding transformer 2 having three windings. The second winding 4 of the multi-winding transformer 2 is connected to the first diode 7, and the first smoothing capacitor 8 connected to the first diode 7 is connected in parallel to the first load 9. . The third winding 5 of the multi-winding transformer 2 is connected to the second diode 10 and is connected to the second smoothing capacitor 12 via the current limiting element 11. The second load 13 is connected in parallel with the second smoothing capacitor 12.

  The error amplifier 14 amplifies the difference between the voltage of the first load 9 and the variable output voltage command. The switching frequency control means 15 receives the variable output voltage command and outputs a triangular wave or a sawtooth wave. 16 outputs a switching frequency control signal. The pulse generating means 17 generates a pulse signal at a timing for driving the switching element 6 by the output of the error amplifier 14 and the output of the oscillator 16, and the driving means 18 drives the switching element 6.

  The operation of the DC power supply device configured as described above will be described below. In the case where the output frequency of the oscillator 16 is constant and the voltage applied to the first load 9 is lowered, and the voltage applied to the second load 13 is not affected by the influence of the operation (hereinafter referred to as the operation). The error amplifier 14 amplifies the voltage difference between the variable output voltage command and the first load 9 and outputs the result to the pulse generating means 15. The pulse generation means 15 compares the output of the error amplifier 14 and the output of the oscillator 16 to output a pulse signal at a timing for driving the switching element 6, and the voltage of the first load 9 is changed to the variable output voltage command. A signal is sent to the drive circuit 18 so as to match, and the switching element 6 is driven. That is, when the voltage of the first load 9 decreases, the ON period of the switching element 6 is expanded, and the energy stored in the multi-winding transformer 2 during the ON period increases, so that the switching element 6 becomes When the power is turned off, the electric power supplied through the first diode 7 increases, and the voltage of the first load 9 is increased. Conversely, when the voltage of the first load 9 rises, the operation is performed by a feedback control operation in which control is performed by shortening the ON period of the switching element 6.

On the other hand, regarding the voltage of the second load 13, the second diode 10 is connected to the switching element 6.
Is connected to the third winding 5 of the multi-winding transformer 2 in the direction of conduction during the ON period, and a resistor or a saturable reactor or the like is interposed between the second diode 10 and the second load 13. A current limiting element 11 for limiting the current is provided. For this reason, the second smoothing capacitor 12 is charged during the ON period of the switching element 6 determined by the pulse generating means 17, and the applied voltage of the second load 13 is the winding 3 of the multi-winding transformer 2. A constant voltage corresponding to the winding number ratio of the winding 5 can be obtained. Here, since the charging time required for the second smoothing capacitor 12 is secured during normal operation, the voltage of the second load 13 is affected even when the voltage of the first load 9 is changed. Absent. The minimum on period (hereinafter referred to as the minimum on period) of the switching element 6 required for charging the smoothing capacitor 12 is a constant of the current limiting element 11 and the smoothing capacitor 12, and the power consumption of the second load 13. Is unambiguously determined.

  Next, the case where the value of the variable output voltage command decreases and the ON period of the switching element 6 needs to be equal to or shorter than the minimum ON period (hereinafter referred to as low voltage operation) will be described. Regarding the control of the voltage applied to the first load 9, feedback control by the error amplifier 14 is performed as in the normal operation. As for the control for keeping the voltage of the second load 13 constant, as shown in FIG. 2, if the ON period of the switching element 6 corresponding to the variable output voltage command Vref is equal to or lower than the voltage point Vs at which the minimum ON period is reached. Then, the switching frequency control means 15 gradually increases the output frequency fsw of the oscillator 16 from fr to fm during normal operation, thereby increasing the number of times the smoothing capacitor 12 is charged. This can be explained by the fact that the control of the voltage applied to the first load 9 is proportional to the drive frequency of the switching element 6 and is proportional to the square of the maximum current that flows. For example, in order to supply electric power equal to the first load 9, if the drive frequency of the switching element 6 is quadrupled, the maximum value of the flowing current becomes 1/2. That is, if the output frequency of the oscillator 16 is quadrupled, the ON period of the switching element 6 output from the pulse generator 15 is ½, so that the charging time to the smoothing capacitor 12 is doubled as a result. A drop in the applied voltage of the second load 13 can be prevented. FIG. 3 shows voltage and current waveforms of each part. In FIG. 3, Vg is an output of the driving means 18, Isw is a current flowing through the switching element 6, Id 7 is a current flowing through the first diode 7, and Id 10 is a current flowing through the second diode 10.

  As described above, in this embodiment, it is possible to realize a DC power supply device having both a variable voltage output and a constant voltage output with a single converter circuit, and it is possible to widen the variable voltage range.

  In the present embodiment, the power source for controlling the switching element 6 is not particularly described. However, the power source is directly supplied from the DC power source 1 or configured as a constant voltage output load similar to the second load 13. May be. In this embodiment, the multi-winding transformer 2 having three windings is used to configure the DC power supply device as non-insulated. However, when the input / output is desired to be isolated, the error amplifier 14 and the pulse frequency control are controlled. An insulating transmission means may be provided for each of the means. In this case, the control power supply on the DC power supply 1 side is supplied directly from the DC power supply 1, or an auxiliary power supply capable of outputting another set of constant voltages by providing a fourth winding in the multi-winding transformer 2. You may make it comprise. In particular, a configuration in which an auxiliary power source is provided when the DC power source 1 is a high voltage, such as when the DC power source 1 is configured by rectification of commercial AC voltage, is effective.

(Embodiment 2)
FIG. 4 is a block diagram of a DC power supply device according to the second embodiment of the present invention.

  In the present embodiment, the transformer is a two-winding transformer 19 with respect to the configuration of the first embodiment, and the winding 4 of the multi-winding transformer 2 in the first embodiment is formed by the winding 21. It differs in that it is configured to also serve as the winding 5 and that one line of the second load 13 is not common to the ground.

  Next, the operation is basically the same as in the first embodiment. During normal operation, the ON period of the switching element 6 is feedback-controlled so that the voltage of the first load 9 is the variable output voltage command. The constant voltage can be applied to the second load by charging the second smoothing capacitor 12 from the diode 10 through the current limiting element 11 during the ON period of the switching element 6. To work. The same applies to the operation of keeping the voltage applied to the second load 13 at a constant voltage by increasing the frequency of the oscillator 16 by the pulse frequency control means 15 during low voltage operation. However, since two outputs are obtained from one winding in a time-sharing manner as described above, a voltage having a switching frequency is applied between one line of the first load 9 and one line of the second load 13. Will not be a common ground.

  As described above, in this embodiment, a DC power supply device having both a variable voltage output and a constant voltage output in one converter circuit can be realized with two winding transformers, and the range of the variable voltage output is expanded. It becomes possible.

  In this embodiment, the power source for controlling the switching element 6 is not particularly described. However, the power source is directly supplied from the DC power source 1 or the third winding is provided in the two-winding transformer 19. Another set of auxiliary power sources capable of outputting a constant voltage may be configured. In particular, a configuration in which an auxiliary power source is provided when the DC power source 1 is configured by rectification of a commercial AC voltage, for example, is effective. Even in this case, the configuration of the first embodiment is similar to that of the same configuration. Thus, one winding can be reduced.

(Embodiment 3)
FIG. 5 is a block diagram of a DC power supply device according to the third embodiment of the present invention.

  In the present embodiment, the variable voltage output and the constant voltage output are insulated outputs from the DC power supply 1 with respect to the configuration of the first embodiment, and the insulation transmission means 22 is used for the insulation transmission of the signal of the error amplifier 14. And the output of the pulse generation means 17 converted into a DC signal by the filter circuit 23 is used as the input of the pulse frequency control means. Since the output pulse width of the pulse generating means 17 becomes narrow during low voltage operation, it is possible to convert this pulse to a DC level proportional to the variable output voltage command by averaging the pulses by the filter circuit 23. Thus, since the variable output voltage command is not used, the insulation output means for the variable output voltage command can be reduced.

  As described above, in this embodiment, in a DC power supply device that has both a variable voltage output and a constant voltage output in one converter circuit, when the input / output needs to be insulated, the value of the variable output voltage command is insulated. The variable voltage range can be expanded without transmission.

(Embodiment 4)
FIG. 6 is a block diagram of a DC power supply device according to the fourth embodiment of the present invention.

In FIG. 6, the DC power source 1 is a power supply source, and is connected in series with the reactor 24 and the switching element 6. The connection point between the switching element 6 and the reactor 24 is also connected to the anode of the first diode 7, and the first smoothing capacitor 8 connected to the cathode of the first diode 7 is connected in parallel with the first load 9. Is done. The secondary winding 25 of the reactor 24 is connected to the second diode 10 and is connected to the second smoothing capacitor 12 via the current limiting element 11. The second load 13 is connected in parallel with the second smoothing capacitor 12. The error amplifier 14 amplifies the difference between the voltage of the first load 9 and the variable output voltage command. The switching frequency control means 15 receives the variable output voltage command and outputs it to the oscillator 16 that outputs a triangular wave or a sawtooth wave. A switching frequency control signal is output. The pulse generating means 17 generates a pulse signal at a timing for driving the switching element 6 by the output of the error amplifier 14 and the output of the oscillator 16, and the driving means 18 drives the switching element 6.

  As described above, in the embodiment of the present invention, the reactor 24 serves as the first winding 3 and the second winding 4 of the transformer 2 in the first embodiment.

  Accordingly, the operation is the same as that of the first embodiment, the oscillator 16 outputs a constant frequency during normal operation, and the control of the switching element 6 is feedback control by the error amplifier 14 to the pulse generating means 17. The first load 9 operates so that a voltage corresponding to the variable output voltage command is applied. A voltage corresponding to the number of turns of the secondary winding 25 of the reactor 24 is applied to the second load 13 with respect to the DC power source 1. Further, at the time of low voltage operation, the output frequency of the oscillator 16 is increased by the switching frequency control means to prevent the applied voltage of the second load 13 that is a constant voltage output from being lowered.

  As described above, in the present embodiment, in the DC power supply device with non-insulated input / output, it is possible to reduce the size and cost by applying a reactor instead of a transformer, and to achieve variable voltage output with one converter circuit. A DC power supply device having a constant voltage output can be realized and the variable voltage range can be expanded.

  As described above, since the DC power supply according to the present invention has both a variable voltage output and a constant voltage output, an error between the reference voltage corresponding to the target temperature as a variable output voltage command and the voltage divided by the thermistor resistance. Can be used for a heat retention device using a heater, a cooling device using a thermoelectric element, and the like.

1 is a block diagram of a DC power supply device according to Embodiment 1 of the present invention. Operation explanatory diagram of switching frequency control of DC power supply device in Embodiment 1 of the present invention Waveform diagram of each part in the first embodiment of the present invention Block diagram of DC power supply apparatus according to Embodiment 2 of the present invention Block diagram of DC power supply apparatus in Embodiment 3 of the present invention Block diagram of DC power supply apparatus according to Embodiment 4 of the present invention Block diagram of a conventional DC power supply Voltage waveform diagram of each part of conventional DC power supply

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Multi-winding transformer 3 First winding of multi-winding transformer 4 Second winding of multi-winding transformer 5 Third winding of multi-winding transformer 6 Switching element 7 First 1 diode 8 first smoothing capacitor 9 first load 10 second diode 11 current-current limiting element 12 second smoothing capacitor 13 second load 14 error amplifier 15 switching frequency control means 16 oscillator 17 pulse generation means 18 Drive means 19 Transformer 20 Transformer first winding 21 Transformer second winding 22 Insulation transmission means 23 Filter circuit 24 Reactor 25 Reactor secondary winding

Claims (4)

A DC power source, a multi-winding transformer having at least three windings, a switching element connected in series with a first winding of the multi-winding transformer with respect to the DC power source, and the multi-winding A first diode connected to a second winding of a transformer and connected to discharge the energy stored in the multi-winding transformer as a current when the switching element is in an off state; A first smoothing capacitor for smoothing the output of the diode, a first load connected in parallel to the first smoothing capacitor, and a third winding of the multi-winding transformer when the switching element is in an ON state. A second diode for rectifying the voltage generated in the winding of the current, a current limiting element for limiting the maximum value of the current flowing through the second diode, and a second for smoothing the current flowing through the current limiting element Amplifying a smoothing capacitor, a second load connected in parallel to the second smoothing capacitor, a variable output voltage command for determining a voltage to be applied to the first load, and a difference between the actually applied voltages An error amplifier, a switching frequency control means for controlling a switching frequency of the switching element in accordance with a value of a variable output voltage command, an oscillator whose oscillation frequency changes according to an output of the switching frequency control means, and an error amplifier DC generator comprising: pulse generation means for generating a pulse for driving the switching element by an output and an output of the oscillator; and drive means for driving the switching element in accordance with the output of the pulse generation means Power supply. A DC power source, a transformer having two windings, a switching element connected in series with the first winding of the transformer with respect to the DC power source, and a second winding of the transformer A first diode connected to discharge the energy stored in the transformer as a current when the switching element is in an off state, and a first smoothing capacitor for smoothing the output of the first diode; A first load connected in parallel to the first smoothing capacitor; a second diode for rectifying a voltage generated in the second winding of the transformer when the switching element is in an on state; A current limiting element for limiting a maximum value of a current flowing through the second diode; a second smoothing capacitor for smoothing a current flowing through the current limiting element; and the second smoothing capacitor. A second load connected in parallel to the driver, an error amplifier for amplifying a difference between a variable output voltage command for determining a voltage applied to the first load and a voltage actually applied, and a variable output voltage command Switching frequency control means for controlling the switching frequency of the switching element in accordance with the value of the oscillator, an oscillator whose oscillation frequency changes according to the output of the switching frequency control means, and the switching by the output of the error amplifier and the output of the oscillator A DC power supply apparatus comprising: pulse generation means for generating a pulse for driving an element; and drive means for driving the switching element in accordance with an output of the pulse generation means. 3. The DC power supply device according to claim 1, wherein the switching frequency control unit is configured to control a switching frequency according to a pulse width of the pulse generation unit. A DC power source, a reactor having a secondary winding, a switching element connected in series to the reactor with respect to the DC power source, and stored in the reactor when connected to the reactor and the switching element is in an OFF state A first diode connected to discharge the generated energy as a current, a first smoothing capacitor for smoothing the output of the first diode, and a first diode connected in parallel to the first smoothing capacitor A load, a second diode for rectifying a voltage generated in the secondary winding of the reactor when the switching element is in an on state, and a current limit for limiting a maximum value of a current flowing through the second diode An element, a second smoothing capacitor for smoothing a current flowing through the current limiting element, and a second smoothing capacitor connected in parallel to the second smoothing capacitor 2, an error amplifier that amplifies a difference between a variable output voltage command that determines a voltage applied to the first load and a voltage that is actually applied, and the switching element according to a value of the variable output voltage command Switching frequency control means for controlling the switching frequency, an oscillator whose oscillation frequency is changed by the output of the switching frequency control means, and a pulse for driving the switching element by the output of the error amplifier and the output of the oscillator A direct-current power supply device comprising: a pulse generating means for generating; and a driving means for driving the switching element in accordance with an output of the pulse generating means.

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