DC power supply device

Abstract

To provide a DC power supply which can satisfy an EMC standard of a class 5 of CISPR25.SOLUTION: In a DC power supply which comprises: a switching power supply (20); and a current stabilization circuit (10) connected with a pre-stage or post-stage of the switching power supply and converts DC input voltage to be supplied from a DC power source to output DC voltage with different potential, the switching power supply comprises: a frequency-variable oscillation circuit which generates an oscillation signal for giving a switching period; and an oscillation control circuit which generates oscillation control voltage or oscillation control current for varying a frequency of the oscillation circuit in a period longer than the switching period.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005] , ,

[0001] The present invention relates to a DC power supply device including a switching power supply and a current stabilization circuit.

Background Art

[0002] In the field of in-vehicle electronic devices, when supplying a DC voltage from a battery to a load through a relatively long power cable, such as in a drive recorder, a switching power supply (DC-DC converter) is provided on the device side to prevent voltage drop and improve efficiency. In such a system where current is supplied from a battery to a switching power supply through a long power cable, conduction noise is superimposed on the power cable due to the switching operation of the power supply device, and radiation noise is emitted from the power cable, which may affect other electronic devices such as a television broadcast receiver.

[0003] In recent years, with the electrification of driving power sources such as EVs (electric vehicles) and PHEVs (plug-in hybrids), and the introduction of advanced driving systems such as autonomous driving, the importance of EMC (electromagnetic compatibility) countermeasures has been increasing, and an EMC standard for automobiles called CISPR25 has been formulated by the IEC (International Electrotechnical Commission). Since a switching power supply (DC-DC converter) used in an automobile is a noise source, it is an essential condition to suppress noise to meet standards such as CISPR25.

[0004] Therefore, the present applicant has focused on the fact that the current flowing through the power cable fluctuates violently due to the switching operation in the DC-DC converter, which causes radiation noise, and has made an invention related to a DC power supply device in which a current stabilization circuit is connected to the front stage or the rear stage of the DC-DC converter, and has filed a prior application (Patent Document 1). In the field of DC power supplies, a spectrum spreading function may be provided as an EMC countermeasure for in-vehicle DC-DC converters.

[0005] Spread spectrum is a technique that suppresses the peak value of electromagnetic noise emitted by electronic devices by distributing its energy across a certain frequency bandwidth. This is achieved by introducing low-frequency jitter, which slightly fluctuates the frequency of the oscillation signal, so that the energy spectrum of the electromagnetic noise emitted by electronic devices does not concentrate in a narrow bandwidth. Patent Document 2 describes the provision of a spread spectrum function as an EMC countermeasure in switching regulators for electronic devices such as mobile phones and PDAs. However, Patent Document 2 does not describe a technique for reducing noise by providing a current stabilization circuit. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-191079 [Patent Document 2] Japanese Patent Publication No. 2011-139609 [Overview of the project] [Problems that the invention aims to solve]

[0007] The inventors of this invention calculated the magnitude of noise transmitted from the input terminal VIN of a DC-DC converter to the upstream power supply side through simulation, comparing a DC power supply with a current stabilization circuit connected before the DC-DC converter with a standalone DC-DC converter (switching frequency 2 MHz) without a current stabilization circuit. The results are shown in Figure 3. Of these, Figure 3(A) shows the frequency spectrum of conducted noise in the case of a standalone DC-DC converter, and Figure 3(B) shows the frequency spectrum of conducted noise when a current stabilization circuit is provided before the DC-DC converter. The horizontal axis in each figure is frequency. In Figures 3(A) and (B), the frequencies of the multiple peaks appearing in the noise correspond to the harmonics frequencies of the switching frequency 2 MHz.

[0008] On the other hand, Figure 2 shows the noise levels for each frequency band (0-10MHz, 10-20MHz, 20-30MHz, ... 90-100MHz) selected as representative values, plotted as noise for 5MHz, 15MHz, 25MHz, ... 95MHz, and represented as line graphs. In Figure 2, line A represents the change in conducted noise for the DC-DC converter alone, and line B represents the change in noise for the DC-DC converter with a current stabilization circuit. Also in Figure 2, NL1, NL2, NL3, and NL4 represent the noise levels for 0.5-1.6MHz, 5.9-6.2MHz, 30-54MHz, and 76-90MHz as specified in CISPR25 Class 5. Figure 2 shows that the conducted noise of both the DC-DC converter alone and the DC-DC converter with a current stabilization circuit does not meet the CISPR25 Class 5 standard.

[0009] Furthermore, the inventors simulated the magnitude of noise transmitted to the power supply side when a spread spectrum function is provided in a DC-DC converter operating at a switching frequency of 2 MHz. The results are shown in Figure 4(A). Figure 2 shows the maximum peaks of conducted noise in each frequency band when the spread spectrum function is provided, indicated by the piecewise line C. From Figure 2, it was found that the conducted noise of the DC-DC converter with the spread spectrum function under predetermined conditions is about the same as the conducted noise when a current stabilization circuit is provided, and does not meet the CISPR25 Class 5 standard. In other words, the DC-DC converter under simulation was under conditions where the noise reduction effect with the spread spectrum function and the noise reduction effect with the current stabilization circuit were approximately the same.

[0010] This invention was made against the background described above, and its objective is to provide a DC power supply that can satisfy the CISPR25 Class 5 EMC standard under conditions where the noise reduction effect is approximately the same whether or not a spread spectrum function is provided in the DC-DC converter or a current stabilization circuit is provided. Another object of the present invention is to provide a DC power supply that can switch its operation according to user requirements or noise specifications. [Means for solving the problem]

[0011] To achieve the above objective, the present invention A DC power supply comprising a switching power supply and a current stabilization circuit connected to the preceding or succeeding stage of the switching power supply, wherein the DC input voltage supplied from a DC power supply is converted to output DC voltages of different potentials, The aforementioned switching power supply device is A frequency-variable oscillator circuit that generates an oscillation signal that provides a switching period, An oscillation control circuit that generates an oscillation control voltage or oscillation control current to change the frequency of the oscillation circuit with a period longer than the switching period, A current bypass path connected between the current input terminal and the current output terminal of the current stabilization circuit, and a current switch element provided in the middle of the current bypass path, An operation switching circuit that generates a signal to control the current switch element to turn on or off in response to an external signal or voltage, Equipped with 、 The oscillation control circuit is configured to be able to switch between a first operating state that changes the generated oscillation control voltage and a second operating state that fixes it. The operation switching circuit is capable of generating a signal to switch the operating state of the oscillation control circuit. The device can operate in one of four operating modes based on the signal generated by the operation switching circuit: a first mode in which the current stabilization circuit operates and the oscillation control circuit of the switching power supply operates in the first operating state; a second mode in which the current stabilization circuit does not operate and the oscillation control circuit operates in the first operating state; a third mode in which the current stabilization circuit operates and the oscillation control circuit operates in the second operating state; and a fourth mode in which the current stabilization circuit does not operate and the oscillation control circuit operates in the second operating state. to composition That is what happened.

[0012] In a DC power supply with the above configuration, the oscillation circuit that generates the oscillation signal that gives the switching period of the switching power supply (DC-DC converter) is frequency-variable, and the frequency of the oscillation circuit is changed by the oscillation control voltage or oscillation control current generated by the oscillation control circuit at a period longer than the switching period, so that the oscillation circuit and oscillation control circuit realize a spread spectrum function. Furthermore, a current stabilization circuit connected to the front stage or the rear stage of the switching power supply device can suppress the transmission of noise generated by the switching operation of the switching power supply device to the power line, thereby suppressing the large fluctuation of the current in the power line and the emission of radiation noise from the power line. As a result, the EMC standard of Class 5 of CISPR25 can be satisfied. Furthermore, since it is configured to operate in any one of the four operating modes, it is possible to realize a DC power supply with functions that meet user requirements without changing the hardware.

Advantages of the Invention

[0013] According to the DC power supply device of the present invention, under the condition that the noise reduction effects when the DC-DC converter is provided with a spectrum spreading function and when a current stabilization circuit is provided are substantially the same, the noise generated during the switching operation can be further reduced to meet the EMC standard of Class 5 of CISPR25. In addition, according to the user's requirements, that is, whether to prioritize noise reduction or voltage drop avoidance, or according to the noise standard, the operation can be switched, which has the effect of improving flexibility and usability.

Brief Description of the Drawings

[0014] [Figure 1] It is a circuit configuration diagram showing an embodiment of the DC power supply device according to the present invention. [Figure 2] It is a line graph showing the maximum peaks in each frequency band in the frequency spectra of the noises in FIGS. 3 and 4 taken as representative values. [Figure 3] (A) is the frequency spectrum of the noise in the case of only the DC-DC converter, and (B) is the frequency spectrum of the noise of the DC-DC converter provided with a current stabilization circuit. [Figure 4] (A) is the frequency spectrum of the noise of the DC-DC converter provided with a spectrum spreading function, and (B) is the frequency spectrum of the noise of the DC-DC converter in the embodiment provided with a current stabilization circuit and a spectrum spreading function. [Figure 5]This is a circuit diagram showing a second embodiment of the DC power supply device according to the present invention. [Modes for carrying out the invention]

[0015] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Figure 1 shows a schematic configuration of one embodiment in which the present invention is applied to a DC power supply device equipped with a switching power supply (DC-DC converter). The DC power supply unit shown in Figure 1 has the function of converting the power supply voltage Vin input from the battery into a voltage suitable for the electronic device load, outputting a stable output voltage Vout, and supplying current Iout to the load. In power supply units for automotive electronic devices, the input voltage Vin is typically 3V to 36V, and the output voltage Vout is 3.3V.

[0016] The DC power supply device of this embodiment consists of a current stabilization circuit 10 equipped with a current input terminal IN1 and a current output terminal OUT1, which controls the current input to the current input terminal IN1 from a battery via a power cable or the like, and a switching control type DC-DC converter 20 equipped with a voltage input terminal IN2 and a voltage output terminal OUT2, with the voltage input terminal IN2 connected to the current output terminal OUT1 of the current stabilization circuit 10, and a load RL connected to the voltage output terminal OUT2 of the DC-DC converter 20.

[0017] While not particularly limited, if the current stabilization circuit 10 and the DC-DC converter 20 are each configured as ICs (semiconductor integrated circuits) mounted on a single board such as a printed circuit board, the current stabilization circuit 10 and the DC-DC converter 20 are connected by power lines (one of which is a ground line) consisting of two printed circuit patterns formed on the board. In addition, a smoothing capacitor C1 is connected between the voltage output terminal OUT1 and the ground point, and a smoothing capacitor C2 is connected between the voltage output terminal OUT2 and the ground point. The current stabilization circuit 10 and the DC-DC converter 20 may also be formed as a single IC on a single semiconductor chip.

[0018] The current stabilization circuit 10 in the DC power supply device of this embodiment includes a current control transistor Q1, which is a PNP bipolar transistor, provided between the current input terminal IN1 to which a DC voltage supplied from the battery is applied and the current output terminal OUT1; a resistor R1 connected between the emitter terminal of the transistor Q1 and the current input terminal IN1; an operational amplifier (operational amplifier circuit) AMP1 that controls the transistor Q1; and a constant voltage source CVS that generates a voltage to be applied to the non-inverting input terminal of the operational amplifier AMP1. A low-resistance element with a resistance value of about 10Ω is used for the resistor R1.

[0019] Furthermore, the current stabilization circuit 10 includes a noise reduction capacitor C1 connected between the current input terminal IN1 and the ground point, and a low-pass filter LPF provided between the current output terminal OUT1 and the negative control terminal (-) of the constant voltage source CVS. In this embodiment, a voltage higher than the output potential of the low-pass filter LPF by the voltage of the constant voltage source CVS is applied to the non-inverting input terminal of the operational amplifier AMP2.

[0020] The low-pass filter (LPF) consists of a resistor R2 connected between the current output terminal OUT1 of the current stabilization circuit 10 and the negative terminal (-) of the constant voltage source CVS, and a capacitor C2 connected between the negative control terminal (-) of the constant voltage source CVS and the ground point. The time constant is set so that the high-frequency component corresponding to the switching frequency of the subsequent DC-DC converter 20 is removed from the voltage fluctuation component of the current output terminal OUT1, and the low-frequency component corresponding to the servo bandwidth (servo control frequency) of the DC-DC converter 20 is allowed to pass through.

[0021] As a result, the low-pass filter (LPF) transmits only the voltage fluctuations at the current output terminal OUT1 associated with the servo control of the subsequent DC-DC converter 20 to the operational amplifier AMP2 via the constant voltage source CVS, while preventing the voltage fluctuations at the current output terminal OUT1 associated with switching control from being transmitted to the operational amplifier AMP2. Specifically, for example, if the switching frequency of the DC-DC converter 20 is 2MHz and the servo control frequency is 2.4kHz, a resistor R2 with a resistance value of several tens of kΩ is used, and a capacitor C2 with a capacitance value of several nF is used.

[0022] Furthermore, the constant voltage source CVS is configured to generate a voltage (approximately 0.2V) equivalent to the collector-emitter voltage VCE of the bipolar transistor, thereby enabling the current control transistor Q1 to operate continuously. Additionally, configuring the voltage to be as low as 0.2V has the advantage of suppressing thermal losses in transistor Q1, thereby minimizing losses in transistor Q1. Moreover, by not making the voltage too low, an increase in the parasitic capacitance of the current control transistor Q1 is prevented. The current stabilization circuit 10 of this embodiment, having the configuration described above, operates to supply a current expressed as Ic = (ΔV - CVS) / R1, where Ic is the collector current flowing through the current control transistor Q1 and ΔV is the potential difference between the current input terminal IN1 and the current output terminal OUT1.

[0023] Here, the potential difference ΔV between the current input terminal IN1 and the current output terminal OUT1 is set to remove high-frequency components associated with the operation of the DC-DC converter 20 and maintain low-frequency components, as described above. Therefore, the current changes on the current output terminal OUT1 side, which fluctuate sharply due to the switching operation of the DC-DC converter 20, are not transmitted to the upstream power line, while a current Ic that changes in accordance with the current changes associated with the servo control of the DC-DC converter 20 can be flowed. Furthermore, the current stabilization circuit 10 is not limited to the circuit with the configuration shown in Figure 1, but may also be a circuit with a configuration such as those described in Figures 3, 5, and 6 of the aforementioned Patent Document 1.

[0024] Next, we will explain the DC-DC converter 20. The DC-DC converter 20 of this embodiment includes a switching transistor M1, which is a P-channel MOSFET (field-effect transistor) connected in series between a voltage input terminal IN2 and a voltage output terminal OUT2, and an inductor L1 connected in series with M1. Furthermore, it includes a synchronous rectifier transistor M2 connected between the connection node of transistor M1 and inductor L1 and the ground point, a switching control circuit 21 that generates signals to control the on and off states of transistors M1 and M2, and a driver (gate drive circuit) 22 that drives transistors M1 and M2 on and off according to the control signal from the switching control circuit 21.

[0025] Furthermore, bleeder resistors Rb1 and Rb2, connected in series, divide the output voltage Vout of the DC-DC converter 20 between the voltage output terminal OUT2 and the ground point. The switching control circuit 21 includes an error amplifier AMP2 to which the voltage divided by the bleeder resistors Rb1 and Rb2 is connected as a feedback voltage VFB to an inverting input terminal; an oscillator circuit OSC that generates a signal of a predetermined frequency; a waveform generation circuit WG which is an oscillator control circuit that generates a control signal to control the frequency of the oscillator circuit OSC; and a comparator (voltage comparator) COMP which takes the output signal of the error amplifier AMP2 and the output signal of the oscillator circuit OSC as inputs.

[0026] A reference voltage Vref is applied to the non-inverting input terminal of the error amplifier AMP2. The error amplifier AMP2 outputs a voltage to the comparator COMP corresponding to the potential difference between the feedback voltage VFB and the reference voltage Vref. The comparator COMP generates a pulse signal that controls the on / off state of transistors M1 and M2 using PWM (pulse width modulation) according to the output voltage of the error amplifier AMP1. This pulse signal controls the on time of switching transistor M1.

[0027] Specifically, transistor M2 is turned off and M1 is turned on to allow current to flow through inductor L1 and store energy. Then, M1 is turned off and M2 is turned on to release the stored energy in inductor L1, allowing current Iout to flow to the voltage output terminal OUT2, and simultaneously converting the input voltage to supply a predetermined DC voltage to the load. Furthermore, when the load current increases and the output voltage Vout decreases, the pulse width of the comparator COMP's output widens, lengthening the on-time of M1 and increasing the output voltage Vout. Conversely, when the load current decreases and the output voltage Vout increases, the pulse width of the comparator COMP's output narrows, shortening the on-time of M1 and lowering the output voltage Vout.

[0028] In the DC-DC converter 20 of this embodiment, a voltage-controlled oscillator (VCO) is used as the oscillator circuit (OSC), whose oscillation frequency is variable according to the voltage applied to the control terminal. On the other hand, the waveform generation circuit WG uses a triangular wave generation circuit that generates a triangular wave that changes at a frequency sufficiently smaller than the switching frequency of the DC-DC converter 20. When the triangular wave generated by this triangular wave generation circuit is applied to the control terminal of the VCO, the oscillation frequency of the VCO repeatedly increases and decreases. Therefore, a spread spectrum function is realized by the VCO and the triangular wave generation circuit.

[0029] Specifically, for example, the fundamental frequency of the oscillator circuit OSC is set to 2 MHz, and the frequency of the triangular wave is set to 3 kHz. The oscillator circuit OSC is configured to repeat the operation of increasing the frequency from 2 MHz to 2.4 MHz and then decreasing it back to 2 MHz with a period of 0.33 milliseconds (3 kHz) due to the change in the triangular wave from the waveform generation circuit WG. In this way, by spreading the switching frequency upward, interference in the AM band due to downward spreading can be avoided. Note that the fundamental frequency of 2 MHz is just one example; generally, any frequency in the range of 200 kHz to 2.2 MHz is selected. Furthermore, although a voltage-controlled oscillator (VCO) is used as the oscillator circuit (OSC) in this embodiment, an oscillator circuit of the type in which the oscillation frequency changes depending on the control current may also be used. In addition, the triangular wave generation circuit may be one that generates sawtooth waves (triangular waves in a broad sense).

[0030] Figure 4(B) shows the frequency spectrum of conducted noise obtained by simulation under the frequency conditions described above for the DC power supply device of this embodiment (DC-DC converter + current stabilization circuit + spread spectrum function), which consists of a current stabilization circuit 10 and a DC-DC converter 20. Based on this frequency spectrum, the noise with the largest peak was selected as a representative value in each frequency band of 0-10MHz, 10-20MHz, 20-30MHz, ... 90-100MHz, and plotted as noise at 5MHz, 15MHz, 25MHz, ... 95MHz. The points were then connected to represent this as a broken line D in Figure 2.

[0031] Figures 2 and 4(B) show that the DC power supply unit of this embodiment (DC-DC converter + current stabilization circuit + spread spectrum function) can meet the EMC standard of CISPR25 Class 5. Furthermore, line D is consistent with the expected result from line B, which represents the characteristics of the DC power supply unit (DC-DC converter + current stabilization circuit), and line C, which represents the characteristics of the DC power supply unit (DC-DC converter + spread spectrum function). Moreover, line D is not the average of the noise peak values ​​in each frequency band of the frequency spectrum shown in Figure 4(B), but rather connects the maximum peak points. From this, it can be seen that the harmonic noise components can be completely suppressed to below the noise level specified in CISPR25 Class 5.

[0032] Next, a second embodiment of the DC power supply device according to the present invention will be described using Figure 5. In the DC power supply device of the second embodiment, a bypass current path is provided between the current input terminal IN1 and the current output terminal OUT1 of the current stabilization circuit 10, bypassing the resistor R1 and the current control transistor Q1, and an on / off switch SW1 is provided in the middle of this bypass current path. Furthermore, an operation switching circuit 30 is provided to switch the operating mode of the circuit in accordance with external control signals E1 and E2. The signal from the operation switching circuit 30 turns the on / off switch SW1 on or off, and also switches the operation of the waveform generation circuit WG of the DC-DC converter 20. The other configurations are the same as in the first embodiment, so the explanations that would be redundant are omitted.

[0033] In the DC power supply of this embodiment, the DC power supply of this embodiment can take on up to four operating states depending on the combination of the on or off state of the switch SW1 and the two states of the waveform generation circuit WG. Specifically, the waveform generation circuit WG performs a first operation in response to a switching signal from the operation switching circuit 30, generating and outputting a triangular wave of a predetermined frequency, similar to the first embodiment, and a second operation in which it outputs a constant voltage. The constant voltage output in the second operation is a voltage that causes the oscillator (VCO) to oscillate at a frequency of, for example, 2 MHz.

[0034] As a result, the operation switching circuit 30 is configured to have a switching function to operate in one of the following modes: a DC power supply with (DC-DC converter + current stabilization circuit + spread spectrum function), a DC power supply with (DC-DC converter + spread spectrum function), a DC power supply with (DC-DC converter + current stabilization circuit), or a DC power supply with DC-DC converter alone. However, the DC power supply may be configured to have a switching function for any two or three of the above four operating modes. Furthermore, it is preferable to configure the current stabilization circuit 10 so that when the on / off switch SW1 is turned on, the operational amplifier AMP1 of the current stabilization circuit 10 stops operating and the current control transistor Q1 is turned off. This reduces the power consumption of the current stabilization circuit 10 during the period when switch SW1 is on.

[0035] In the first and second embodiments, a current stabilization circuit 10 is provided to reduce noise, and the current stabilization circuit 10 is provided with a resistor R1 for detecting the output current value, so the output voltage is lower compared to when the current stabilization circuit 10 is not provided. On the other hand, some users prioritize avoiding a decrease in output voltage over noise reduction, while others prioritize noise reduction over avoiding a decrease in output voltage. The DC power supply of the second embodiment includes a switch SW1 for bypassing the IN1-OUT1 section of the current stabilization circuit 10 and an operation switching circuit 30, so it can be operated as a power supply prioritizing noise reduction or as a power supply prioritizing avoiding output voltage degradation. Furthermore, the power supply may be configured to switch operation according to the noise standard, such as CISPR25 Class 5 and Class 4.

[0036] Furthermore, when the current stabilization circuit 10, the DC-DC converter (excluding L1, C4, Rb1, Rb2) 20, and the operation switching circuit 30 are configured as a single IC, external terminals (pins) or pads may be provided for inputting control signals E1 and E2 to the operation switching circuit 30. In this case, external pull-up resistors or pull-down resistors can be connected to the external terminals (pins) or pads to serve as substitutes for the control signals E1 and E2. In addition, a register may be provided to hold the state of the control signals E1 and E2 input to the operation switching circuit 30.

[0037] Although the present inventors' invention has been described in detail above based on embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiments, a waveform generation circuit WG that generates a continuously changing triangular wave is provided, but instead of the waveform generation circuit WG, a circuit that generates a voltage or signal that changes the oscillation frequency of the oscillator (VCO) in steps (oscillation frequency variation means) may be provided. Furthermore, although the above embodiment shows a DC power supply device in which the current stabilization circuit 10 is provided before the DC-DC converter 20, it may also be configured as a DC power supply device in which the current stabilization circuit 10 is provided after the DC-DC converter 20.

[0038] Furthermore, although the above embodiment shows a system in which a bipolar transistor is used as the transistor constituting the current stabilization circuit 10, a MOS transistor may be used instead of a bipolar transistor. In addition, although the above embodiment describes a DC power supply device using a synchronous rectification type DC-DC converter as the DC-DC converter 20, an asynchronous rectification type DC-DC converter using a diode instead of a switching transistor M2 may be used. Furthermore, although the above embodiment described the case in which the present invention is applied to a system in which a non-isolated DC-DC converter is used as a DC power supply device, the present invention can also be applied to a system in which an isolated DC-DC converter equipped with a transformer and switching-controlled the current flowing through the primary winding is used as a DC power supply device. [Explanation of Symbols]

[0039] 10...Current stabilization circuit, Q1...Current control transistor, AMP1...Amplifier, LPF...Low-pass filter, CVS...Constant voltage source, 20...DC-DC converter (switching power supply), 21...Switching control circuit, 22...Driver (drive circuit), 30...Operation switching circuit, L1...Inductor (coil), AMP2...Amplifier, COMP...Comparator (voltage comparator), OSC...Oscillator circuit, WG...Waveform generation circuit (oscillation control circuit), SW1...On / off switch (current switching element)

Claims

1. A DC power supply comprising a switching power supply and a current stabilization circuit connected to the preceding or succeeding stage of the switching power supply, wherein the DC input voltage supplied from a DC power supply is converted to output DC voltages of different potentials, The aforementioned switching power supply device is A frequency-variable oscillator circuit that generates an oscillation signal that provides a switching period, An oscillation control circuit that generates an oscillation control voltage or oscillation control current to change the frequency of the oscillation circuit with a period longer than the switching period, A current bypass path connected between the current input terminal and the current output terminal of the current stabilization circuit, and a current switch element provided in the middle of the current bypass path, An operation switching circuit that generates a signal to control the current switch element to turn on or off in response to an external signal or voltage, Equipped with, The oscillation control circuit is configured to be able to switch between a first operating state in which the generated oscillation control voltage is changed and a second operating state in which it is fixed. The operation switching circuit is capable of generating a signal to switch the operating state of the oscillation control circuit. A DC power supply device characterized in that it is configured to operate in one of four operating modes based on a signal generated by the operation switching circuit: a first mode in which the current stabilization circuit operates and the oscillation control circuit of the switching power supply device operates in the first operating state; a second mode in which the current stabilization circuit does not operate and the oscillation control circuit operates in the first operating state; a third mode in which the current stabilization circuit operates and the oscillation control circuit operates in the second operating state; and a fourth mode in which the current stabilization circuit does not operate and the oscillation control circuit operates in the second operating state.

2. The current stabilization circuit comprises a current control transistor provided between a current input terminal and a current output terminal, and an operational amplifier circuit that controls the transistor according to the voltage at the current output terminal, The DC power supply device according to claim 1, characterized in that the operation of the operational amplifier circuit is stopped when the current switch element is turned off by a signal generated by the operation switching circuit.

3. The oscillator circuit is a voltage-controlled oscillator circuit in which the oscillation frequency can be changed according to the applied voltage. The oscillation control circuit is a triangular wave generation circuit that generates a triangular wave in which the voltage value gradually increases and decreases. The DC power supply device according to claim 1 or 2, characterized in that the triangular wave generated by the triangular wave generation circuit is applied to the oscillation circuit as a voltage that changes the oscillation frequency.

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