JP2010124567A - Switching power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply device which can obtain high power conversion efficiency and can be reduced in size and cost by forming a one-stage constitution by integrating a PFC circuit having a harmonic suppression function and an insulated DC-DC converter. <P>SOLUTION: The switching power supply device is characterized by comprising: a rectification circuit which rectifies AC power; a transformer in which one end of a primary-side coil is connected to a positive electrode terminal of the rectification circuit, and the primary-side coil and a secondary-side coil are constituted so as to be reverse in polarity; a switching element one end of which is connected to a negative electrode terminal of the rectification circuit and the other end of which is connected to the other end of the primary-side coil, and which turns on and off a current flowing to the primary-side coil by a pulse signal; a diode whose anode is connected to one end of the secondary-side coil so as to block a current of the secondary-side coil when the current flows to the primary-side coil; and a smoothing capacitor one end of which is connected to a cathode of the diode and the other end of which is connected to the other end of the secondary-side coil. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply device, and more particularly to an isolated switching power supply device having a power factor correction function.

  Recently, a switching power supply (AC / DC converter) provided with a PFC (Power Factor Correction) circuit for the purpose of power factor improvement and harmonic suppression has become widespread.

  When the input side of the AC / DC converter is simply composed of a full-wave diode rectifier circuit and a smoothing capacitor, the output voltage waveform of the diode rectifier circuit is an AC full-wave rectifier waveform, but the current waveform is a spiked waveform. It is known to be. That is, the voltage waveform and the current waveform are not similar. For this reason, the power factor of various apparatuses incorporating such an AC / DC converter is lowered, which is not preferable from the viewpoint of energy use efficiency as well as for the power supplier.

  Spike-shaped current waveforms have many harmonic components, especially odd-order harmonic components, and if these harmonic components flow into the power line, an unexpected accident may occur in the transmission and distribution equipment. is there. For this reason, standards for regulating harmonic components are provided in each country.

  As described above, the necessity for improving the power factor of the AC / DC converter is increasing, and various switching power supplies incorporating a PFC circuit for the purpose of improving the power factor have been developed.

For example, Patent Document 1 discloses a technique related to a switching power supply device including a PFC circuit and a DC / DC converter.
JP 2006-187115 A

  In general, the PFC circuit has a non-insulated boost converter as a basic configuration, and includes a choke coil, a diode, a switching FET, and the like. For example, a commercial AC power supply of about 100V to 240V is rectified, and the rectified voltage is boosted to a DC voltage of about 400V by a non-insulated boost converter. At this time, the duty ratio of the switching pulse is controlled so that the input current waveform of the PFC circuit is similar to the input voltage waveform.

  On the other hand, when converting from a commercial power source to a direct current of a desired voltage, insulation is often required between the commercial power source and the output. For this reason, a general AC / DC converter has a two-stage configuration of a PFC circuit having a boosting converter as a basic configuration and an insulated DC / DC converter. That is, similar switching converters are connected in two stages in series.

  As a result, not only the power conversion efficiency is lowered, but also an obstacle to downsizing and cost reduction of the apparatus.

  The present invention has been made in view of the above circumstances, and a PFC circuit having a harmonic suppression function and an insulated DC / DC converter can be integrated into a single stage to obtain high power conversion efficiency. Another object of the present invention is to provide a switching power supply device that can be reduced in size and cost.

  In order to solve the above-described problems, a switching power supply according to the present invention includes a rectifier circuit that rectifies an AC power supply in a switching power supply including an active power factor correction converter and an insulating DC / DC converter in a single stage. One end of the primary side coil is connected to the positive terminal of the rectifier circuit, the primary side coil and the secondary side coil are configured to have opposite polarities, one end is connected to the negative terminal of the rectifier circuit, and the other An end is connected to the other end of the primary side coil, and a switching element that turns on and off a current flowing through the primary side coil by a pulse signal; and a current of the secondary side coil when a current flows through the primary side coil A diode having an anode connected to one end of the secondary coil and one end connected to the cathode of the diode so as to block current. The other end is characterized in that and a smoothing capacitor connected to the other end of the secondary coil.

  According to the switching power supply device of the present invention, the PFC circuit having the harmonic suppression function and the insulation type DC / DC converter are integrated into a single stage configuration, and high power conversion efficiency can be obtained. Cost reduction can be realized.

(1) Configuration of Conventional Switching Power Supply Device First, in order to clarify the features of the switching power supply device according to the present invention, a typical configuration of a conventionally used switching power supply device will be outlined.

  FIG. 1 is a diagram for explaining the necessity of a PFC circuit. FIG. 1A shows a configuration of a power supply apparatus 100 that is not provided with a PFC circuit. The power supply circuit that includes only a rectifier circuit 102 and a smoothing capacitor 103 converts the AC power supply 101 into a direct current and converts it into a load 104. DC power is supplied.

  When the smoothing capacitor 103 is not provided, the full-wave rectified voltage waveform shown in FIG. 1B is applied to the load 104. Actually, the full-wave rectified voltage waveform is smoothed by the smoothing capacitor 103, and FIG. ) Is a voltage waveform as shown by a solid line. Since the smoothing capacitor 103 is not charged from the rectifier circuit 102 during the period when the voltage of the smoothing capacitor 103 is higher than the full-wave rectified voltage, the output current of the rectifier circuit 102 is as shown in FIG. It flows only in a short period near the peak of the wave rectified voltage waveform. For this reason, the voltage waveform and the current waveform when viewed from the AC power supply 101 side are not similar, and the power factor is reduced. The current waveform having a steep peak includes many harmonic components, and the harmonic components flow to the AC power supply 101 side.

  In order to improve the power factor and suppress the harmonic component, the output current waveform of the rectifier circuit 102 may be brought close to a full-wave rectified voltage waveform, and a PFC circuit (so-called active PFC circuit) performs this. Circuit.

  FIG. 2 is a diagram illustrating a typical configuration example of a conventional switching power supply device including the PFC circuit 200. The conventional switching power supply device includes, for example, a common mode filter 400, a rectifier circuit 102, a PFC circuit 200, and an insulated DC / DC converter 300 in order from the AC power supply 101 side.

  The common mode filter 400 is a filter provided mainly to block common mode noise. The rectifier circuit 102 is a full-wave rectifier circuit configured by, for example, a diode bridge circuit as illustrated.

  The PFC circuit 200 mainly includes a choke coil 201, a diode 202, a smoothing capacitor 203, and an FET 204 that operates as a switching element. In addition, the input capacitor 210, the voltage monitor resistor 206 for monitoring the output voltage of the rectifier circuit 102, the current monitor resistor 207 for monitoring the output current of the rectifier circuit 102, and the output voltage of the PFC circuit 200 are monitored. Dividing resistors 208 and 209 are provided.

  The input capacitor 210 is mainly for smoothing the switching frequency component, and is a film capacitor, for example. The smoothing capacitor 203 is mainly for smoothing the frequency component of the AC power supply, and is, for example, an electrolytic capacitor.

  As can be seen from the configuration of FIG. 2, the PFC circuit 200 generally has a configuration of a step-up switching converter. For example, when the effective value of the AC power supply voltage is in the range of 100V to 240V, the output voltage of the PFC circuit 200 (the voltage across the smoothing capacitor 203) is boosted to the range of 360V to 420V.

  The switching frequency of the FET 204 is not particularly limited. For example, the FET 204 is switched by a pulse signal having a frequency of about 100 kHz.

  FIG. 3 is a diagram illustrating an operation example of the PFC circuit 200. FIG. 3A shows a voltage waveform (full-wave rectified waveform) and a current waveform (current waveform flowing through the resistor 207) on the output side of the rectifier circuit 102. FIG. While the FET 204 is on, the full-wave rectified voltage is applied to the choke coil 201 and the current increases. On the other hand, when the FET 204 is off, the current flows from the choke coil 201 to the smoothing capacitor 203 via the diode 202 and is output. The current decreases. In this way, the current waveform has a triangular waveform synchronized with the pulse signal applied to the FET 204.

  The PFC circuit 200 has a pulse signal on-period (so that the output voltage of the PFC circuit 200 becomes a predetermined voltage and the envelope of the peak of the current waveform is similar to the output voltage (full-wave rectified waveform)). That is, the duty ratio is controlled by the control circuit (1).

  The triangular wave current flowing through the resistor 207 is smoothed by the input capacitor 210, and the output voltage waveform and the output current waveform of the rectifier circuit 102 are similar. As a result, the voltage waveform and the current waveform at the input terminal of the common mode filter 400 are both sine wave waveforms having the same phase as shown in FIG. 3B, and the power factor is a value close to 1. Further, the harmonic component of the current waveform is also suppressed.

  The conventional PFC circuit 200 is generally based on a non-insulated boost converter, and generally has a configuration in which an isolated converter, for example, a forward converter, is provided downstream of the PFC circuit 200.

  The forward converter 300 includes an insulating transformer 303 as shown in FIG. 2, and a choke coil 301, a regenerative capacitor 302, and an FET 304 as a switching element are connected to the primary side. On the secondary side, a diode 305, a smoothing capacitor 306, and voltage dividing resistors 307 and 308 for voltage monitoring are provided.

  The duty ratio of the pulse signal applied to the FET 304 is controlled by the control circuit (2) so that the output voltage monitored via the voltage dividing resistors 307 and 308 becomes a predetermined value.

  As shown in FIG. 2, the conventional circuit configuration is a two-stage configuration including a PFC circuit 200 and a forward converter 300. Although the power factor improvement and the harmonic suppression function are realized by the PFC circuit 200, the power conversion efficiency decreases due to the presence of the PFC circuit 200. Further, the provision of the PFC circuit 200 increases the number of parts and increases the size of the apparatus. In addition, the cost will increase.

(2) Configuration of Switching Power Supply Device According to First Embodiment of the Present Invention A switching power supply device 1 according to an embodiment of the present invention has a power factor improvement / harmonic suppression function equivalent to the PFC circuit 200 described above. However, it has an insulating function and is realized by a single-stage switching converter.

  FIG. 4 is a diagram illustrating a configuration example of the switching power supply device 1 according to the first embodiment. The switching power supply device 1 is configured as a one-stage switching converter including an FET 11 functioning as a switching element, a flyback transformer 12, a diode 13, a smoothing capacitor 14, and a control circuit 17 as main components.

  The flyback transformer 12 is configured such that the primary coil 12a and the secondary coil 12b have opposite polarities, and the corresponding polarities are indicated by black circles.

  In addition, a common mode filter 400 and a rectifier circuit 102 are provided on the input side of the AC power supply 101 as in the conventional configuration shown in FIG.

  Also, an input current monitor resistor 16 for monitoring a current flowing through the primary coil 12a (hereinafter referred to as input current), and an input voltage monitor resistor 15 for monitoring the voltage at the output terminal of the rectifier circuit 102 (hereinafter referred to as input voltage). It has.

  One end of the primary side coil 12 a is directly connected to the positive terminal of the rectifier circuit 102, and the other end of the primary side coil 12 a is connected to one end of the FET 11. The other end of the FET 11 is connected to the negative terminal of the rectifier circuit 102 via the input current monitor resistor 16.

  On the other hand, the secondary side coil 12b of the flyback transformer 12 has voltage dividing resistors 18 and 19 for monitoring the voltage across the smoothing capacitor 14 (hereinafter referred to as output voltage), and the current flowing through the secondary side coil 12b. An output current monitor resistor 20 for monitoring (hereinafter referred to as output current) is provided.

  The output voltage and output current are converted into appropriate signal levels by the output voltage / output current detection circuit 21, and after being secured by the photocoupler 22, are input to the control circuit 17.

  The operation of the switching power supply device 1 configured as described above will be described. FIG. 5 is a timing chart for explaining the intermittent mode in the switching operation of the switching power supply device 1.

  FIG. 5A is a diagram illustrating a pulse signal applied to the FET 11. When the FET 11 is on, an input current shown in FIG. 5B flows through the primary coil 12a of the flyback transformer 12. The direction of the input current is the direction of the arrow shown in the vicinity of the primary coil 12a in FIG. At this time, since the primary side coil 12a and the secondary side coil 12b have opposite polarities, the induced electromotive force generated in the secondary side coil 12b has the opposite polarity to the primary side. For this reason, it is interrupted by the diode 13 and no current flows to the secondary coil 12b. The primary coil 12a functions as a choke coil, and energy is stored in the primary coil 12a.

  When the FET 11 is turned off, no current flows through the primary coil 12a and the input current becomes zero. On the other hand, the energy accumulated in the primary coil 12a during the ON period is released to the load side via the secondary coil 12b. The direction of the output current is the direction of the arrow shown in the vicinity of the secondary coil 12b in FIG. 4 and flows through the diode 13 to the load side. As shown in FIG. 5C, the output current takes a maximum value immediately after the FET 11 is turned off, decreases with the release of energy, and becomes zero before the next on-period starts.

  FIG. 5D shows a combined current obtained by virtually synthesizing the input current flowing through the primary coil 12a and the output current flowing through the secondary coil 12b. This combined current has a period in which it temporarily becomes zero immediately before the FET 11 is turned on. For this reason, such a switching mode is called an intermittent mode.

  The configuration of the switching power supply device 1 shown in FIG. 4 is similar to a configuration called a so-called flyback converter. The primary side and the secondary side are insulated by a flyback transformer 12 and the pulse signal applied to the FET 11 is changed. The output voltage can be controlled to a predetermined value by duty ratio control.

  One of the features of the switching power supply device 1 according to the present invention is that the function of the PFC circuit is added while basically maintaining this configuration. That is, on the primary side of the flyback transformer 12, the input voltage (the same voltage as the full-wave rectified voltage output from the rectifier circuit 102) and the input current are monitored, and the pulse applied to the FET 11 so that the waveforms of both are similar. By controlling the duty ratio of the signal, a function equivalent to that of a conventional PFC circuit can be obtained, and a DC stabilized power supply having an insulating function by the flyback transformer 12 can be realized. This is one of the important points of interest in the switching power supply device 1 according to the present invention.

  FIG. 6 is a diagram for explaining that the power factor improvement effect and the harmonic suppression effect are obtained in the switching power supply device 1 according to the present embodiment. The difference from the operation of the conventional PFC circuit (see FIG. 3) is that the current waveform is replaced by the current waveform (FIG. 5B) flowing through the primary coil 12a, but is smoothed by the input capacitor 10. Therefore, in the end, a current waveform similar to the voltage waveform can be obtained. As a result, as shown in FIG. 6B, the AC voltage waveform and the AC current waveform seen at the input end of the common mode filter 400 are similar, the harmonics are suppressed, and the power factor is approximately 1.

  According to the switching power supply device 1 according to the present embodiment, in addition to being able to achieve harmonic suppression and power factor improvement as described above, the converter insulated from the AC power supply has a single-stage configuration. Thus, the power conversion efficiency can be improved as compared with the two-stage configuration of the non-insulated PFC circuit and the isolated converter.

  Further, in the conventional configuration example, as shown in FIG. 2, two choke coils 201 and 301, two FETs 204 and 304, two smoothing capacitors 203 and 306, and an insulating transformer 303 are required. In contrast, the switching power supply device 1 according to the present embodiment has a configuration in which the two choke coils 201 and 301 and the insulating transformer 303 are replaced with one flyback transformer 12. Further, one switching element (FET 11) and one smoothing capacitor 14 are sufficient.

  Thus, in the switching power supply device 1 according to the present embodiment, the number of parts is greatly reduced, and the device can be reduced in size and cost.

  The switching power supply device 1 according to the present embodiment can also be operated in a continuous mode.

  FIG. 7 is a diagram illustrating the switching operation in the continuous mode. The continuous mode is an operation mode in which the energy accumulated in the flyback transformer 12 does not become zero but increases or decreases around a certain level. When the FET 11 is turned on, the input current flowing through the primary coil 12a starts increasing from a certain finite value instead of from zero as shown in FIG. Further, as shown in FIG. 7C, the output current flowing through the secondary coil 12b does not become zero while the FET 11 is off. For this reason, the combined current obtained by combining the current flowing through the primary coil 12a and the current flowing through the secondary coil 12b becomes a continuous current that repeatedly increases and decreases around a certain DC level (see FIG. 7D).

  Even in the continuous mode, the power factor improvement effect and the harmonic suppression effect can be obtained in the same manner as in the intermittent mode. FIG. 8 is a diagram showing this, except that the current flowing through the primary coil 12a changes from a triangular wave to a trapezoidal switching waveform. In either case, the current waveform after the switching frequency component is removed by the input capacitor 10 is similar to the voltage waveform. When viewed at the input end of the common mode filter 400, the waveform is the same regardless of whether the mode is continuous mode or intermittent mode.

  By the way, in the duty ratio control by the control circuit 17, in addition to using the input voltage, the input current, and the output voltage, control using the output current may be further performed.

  For example, it is effective to actually synthesize an input current monitor signal and an output current monitor signal and use them for duty ratio control. FIG. 9 is a diagram showing this state. The input current is detected by the input monitor resistor 16 and input to the control circuit 17. On the other hand, the output current is detected by the output current monitor resistor 20 and input to the output voltage / output current detection circuit 21. The output current monitor signal is level-adjusted here and is input to the control circuit 17 via the photocoupler 22 (a signal indicated by hatching in FIG. 9C).

  In the control circuit 17, the monitor signal for the input current and the monitor signal for the output current are actually combined, and the continuous waveform shown in FIG. 9D is used for controlling the duty ratio. Many general-purpose controllers (control circuits) distributed on the market are based on the assumption that a continuous signal is used as an input signal for current control, and a general-purpose inexpensive controller can be used by the above-described synthesis processing.

  In addition, when operated in the continuous mode, an unstable phenomenon may occur in which the output current flowing through the secondary coil 12b varies greatly and slowly. In order to prevent such a phenomenon, a method of controlling by feeding back the secondary current is effective.

  Further, when the output current greatly fluctuates beyond a predetermined range, the control circuit 17 may detect an abnormality and output an abnormality signal to that effect to the outside.

(3) Second Embodiment FIG. 10 is a diagram illustrating a configuration example of a switching power supply device 1a according to a second embodiment. The switching power supply device 1a according to the second embodiment includes a switching element (FET 11A), a transformer (flyback transformer 12A), and a diode 13A among the components of the switching power supply device 1 according to the first embodiment. The first circuit unit 30 </ b> A and the second circuit unit 30 </ b> B having the same configuration as the first circuit unit 30 </ b> A (n is an integer satisfying n ≧ 2). A total of n first and second circuit units having the same configuration are connected in parallel to each other.

  Further, the control circuit 17a gives a pulse width of T / n, where the period T is approximately divided into n, where T is the period of the pulse signal for each of the n FETs of the first and second circuit units. A pulse signal having a phase is shifted and supplied by T / n.

  FIG. 10 is a diagram illustrating an example of a configuration in which n is 2 (that is, a configuration having the first circuit unit 30A and one second circuit unit 30B).

  FIG. 11 is a diagram illustrating a switching operation of each unit corresponding to the configuration example of FIG. FIGS. 11A to 11C show waveforms corresponding to the first circuit unit 30A, FIG. 11A shows a switching pulse signal for the FET 11A, and FIG. 11B shows a primary coil of the flyback transformer 12A. Current flowing through 12aA (ie, input current of the first circuit unit 30A), FIG. 11C shows current flowing through the secondary coil 12bA of the flyback transformer 12A (ie, output current of the first circuit unit 30A). It is.

  Similarly, FIGS. 11D to 11F show waveforms corresponding to the second circuit unit 30B, FIG. 11D shows the switching pulse signal for the FET 11B, and FIG. 11E shows the flyback transformer 12B. The current flowing through the primary side coil 12aB (ie, the input current of the second circuit unit 30B), FIG. 11F shows the current flowing through the secondary side coil 12bB of the flyback transformer 12B (ie, the second circuit unit 30B). Output current). Both the first and second circuit units 30A and 30B are operated in the continuous mode.

  In the configuration example of FIG. 10, the total number of the first and second circuit units is 2, and as described above, for each FET 11A, 11B, the pulse width is T / 2 and the phase is only T / 2. A shifted pulse signal is applied (see FIGS. 11A and 11D).

  As a result, a pulse current that is turned on and off every half cycle flows through the flyback transformers 12A and 12B, and a synthesized signal obtained by synthesizing the input current and output current is shown in FIGS. As shown in h), it becomes a continuous current.

  In the switching power supply device 1a according to the second embodiment, since the combined input current and output current are both continuous currents, ripples due to switching are suppressed.

  Further, since the output current is continuous, the average current becomes a large value, and even if the output voltage is the same, more DC power can be obtained as compared with the case where the current is intermittent. In addition, when trying to obtain the same DC power, a smaller output voltage is required as compared with the case where the current is intermittent, and therefore there is an advantage that parts such as the smoothing capacitor 14 can be made small.

  As described above, according to the switching power supply devices 1 and 1a according to the present embodiment, the PFC circuit having the harmonic suppression function and the insulated DC / DC converter are integrated into a single stage configuration, and high power conversion is achieved. Efficiency can be obtained, and miniaturization and cost reduction can be realized.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined.

The figure explaining the necessity of the power factor improvement in a DC power supply, and harmonic suppression. The figure which shows the structural example of the switching power supply device of the conventional 2 step | paragraph structure type | mold provided with a PFC circuit. The figure explaining generally the power factor improvement and harmonic suppression operation by a PFC circuit. The figure which shows the structural example of the switching power supply device which concerns on the 1st Embodiment of this invention. The timing chart explaining the switching operation in the intermittent mode in the switching power supply device according to the first embodiment. The figure which shows the voltage waveform and current waveform of each part in intermittent mode in the switching power supply device which concerns on 1st Embodiment. The timing chart explaining the switching operation in the continuous mode in the switching power supply device according to the first embodiment. The figure which shows the voltage waveform and current waveform of each part in continuous mode in the switching power supply device which concerns on 1st Embodiment. Explanatory drawing of the operation | movement which feeds back the secondary side current (output current) of a flyback transformer, synthesize | combines with an input current, and utilizes it for duty ratio control. The figure which shows the structural example of the switching power supply device which concerns on the 2nd Embodiment of this invention. The figure which shows the voltage waveform and current waveform of each part in continuous mode in the switching power supply which concerns on 2nd Embodiment.

Explanation of symbols

1, 1a Switching power supply device 10 Input capacitor 11 FET (switching element)
12 Flyback transformer (transformer)
13 Diode 14 Smoothing Capacitor 15 Input Voltage Monitor Resistor 16 Input Current Monitor Resistor 17 Control Circuit 18, 19 Voltage Dividing Resistor 20 Output Current Monitor Resistor 22 Photocoupler 30A First Circuit Unit 30B Second Circuit Unit 101 AC Power Supply 102 Rectifier Circuit 104 Load 400 Common mode filter

Claims (8)

In a switching power supply unit comprising an active type power factor correction converter and an isolated type DC / DC converter in a single stage,
A rectifier circuit for rectifying an AC power supply;
A transformer in which one end of the primary side coil is connected to the positive terminal of the rectifier circuit, and the primary side coil and the secondary side coil are configured to have opposite polarities;
One end is connected to the negative terminal of the rectifier circuit, the other end is connected to the other end of the primary side coil, a switching element for turning on and off the current flowing through the primary side coil by a pulse signal;
A diode having an anode connected to one end of the secondary side coil so as to block the current of the secondary side coil when a current flows through the primary side coil;
A smoothing capacitor having one end connected to the cathode of the diode and the other end connected to the other end of the secondary coil;
A switching power supply device comprising: A control circuit for controlling a duty ratio of the pulse signal;
The control circuit includes:
Monitoring an input voltage generated between the positive terminal and the negative terminal of the rectifier circuit, an input current flowing from the positive terminal to the negative terminal, and an output voltage generated at both ends of the smoothing capacitor;
The duty ratio of the pulse signal is controlled so that the voltage waveform of the input voltage and the current waveform of the input current are similar and the output voltage has a predetermined voltage value.
The switching power supply device according to claim 1. The control circuit includes:
Further monitoring the output current flowing through the secondary coil,
A combined current obtained by synthesizing an input current flowing through the primary coil when the switching element is on and an output current flowing through the secondary coil when the switching element is off has a predetermined current value. Further controlling the duty ratio of the pulse signal;
The switching power supply device according to claim 2. The control circuit includes:
Further monitoring the output current flowing through the secondary coil,
When the output current exceeds a predetermined threshold value, an abnormal signal is notified to that effect.
The switching power supply device according to claim 2. An intermittent mode in which the current flowing in the secondary coil is intermittent during the period in which the switching element is off, and a continuous mode in which the current flowing in the secondary coil is not interrupted even in the period in which the switching element is off, It can operate in any mode,
The switching power supply device according to claim 1. A first circuit unit composed of the transformer, the switching element, and the diode is connected in parallel to each other, and has (n−1) (n ≧ 2) second circuit units having the same configuration as the first circuit unit. Further comprising two circuit units,
The control circuit includes:
A pulse having a pulse width obtained by dividing the period T of the pulse signal by approximately n equally is supplied to each of the switching elements of the total of n first and second circuit units by shifting the phase by T / n.
The switching power supply device according to claim 2. A common mode filter is further provided on the input side of the rectifier circuit,
The switching power supply device according to claim 1. The signal for monitoring the output voltage and the signal for monitoring the output current are input to the control circuit via a photocoupler.
The switching power supply device according to claim 3.

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