JP4899709B2 - Switching power supply device and electronic device - Google Patents

Description

  The present invention relates to a switching power supply device, in particular, a switching power supply device including a plurality of output terminals, and an electronic device including the same.

  As a conventional switching power supply device, commercial AC power supply voltage is rectified by a rectifier diode bridge, and the rectified non-smooth voltage is applied to the primary winding of the transformer to perform switching by the switching element. A converter that obtains a DC output voltage by rectifying and smoothing the voltage obtained in the secondary winding is known.

  In such a converter without a smoothing capacitor on the primary side, the DC voltage output from the secondary side is detected, and the switching element is turned on by PWM control so that the average value of the DC voltage becomes a substantially constant voltage. The duty ratio is controlled. As a result, the input current flows even in a low voltage period other than the vicinity of the peak of the commercial AC power supply voltage, and the current flows throughout one cycle of the commercial AC power supply voltage, so that the harmonic current is suppressed.

  In addition, a rectifier diode and a smoothing capacitor are provided in the secondary winding of the transformer to form a flyback converter unit that outputs the first DC voltage, and a connection point in which the primary winding of the transformer and the switching element are connected in series. Furthermore, Patent Document 1 discloses a switching power supply device in which a boost converter unit that outputs a second DC voltage by connecting a rectifier diode and a smoothing capacitor is disclosed.

A circuit configuration with reference to Patent Document 1 will be described below with reference to the drawings. FIG. 1A shows a circuit configuration of the switching power supply device.
The switching power supply apparatus 100 includes an input unit 113 that receives a commercial AC power supply voltage. The input unit 113 includes a full-wave rectifier circuit Da and a capacitor C3. The input side of the full-wave rectifier circuit Da is connected to an input terminal 123-133 of a commercial AC power supply. On the output side of the full-wave rectifier circuit Da, a capacitor C3 is cascaded as a filter that cuts high-frequency components. A primary winding N1 of the transformer T and a switching circuit unit 115 in which a switching element Q1 is connected in series are cascade-connected to the input unit 113, and one end of the switching element Q1 is connected to the primary side ground 131. More specifically, one end on the output side of the full-wave rectifier circuit Da is connected to the primary winding N1 of the transformer T, and the other end is connected to the primary side ground 131. One end of the switching element Q1 is connected to the output side of the full-wave rectifier circuit Da via the primary winding N1, and the other end of the switching element Q1 is connected to the primary side ground 131.

  In addition, the switching power supply device 100 includes a first rectifying and smoothing circuit 112 for outputting an insulated DC voltage from the secondary side of the transformer T. The first rectifying / smoothing circuit 112 includes a rectifying diode D2 and a smoothing capacitor C2. The first rectifying and smoothing circuit 112, the input unit 113, and the switching circuit unit 115 constitute a flyback converter unit 102.

  The switching power supply device 100 further includes a second rectifying / smoothing circuit 111 for outputting a non-insulated DC voltage from the primary side of the transformer T. The second rectifying / smoothing circuit 111 includes a rectifying diode D1 and a smoothing capacitor C1. The second rectifying / smoothing circuit 111, the input unit 113, and the switching circuit unit 115 constitute a boost converter unit 101.

  In the switching power supply device 100 having such a configuration, the input voltage Vin is an AC voltage of a commercial AC power supply (for example, 100 V, 50 Hz), and the voltage is input to the full-wave rectifier circuit Da. The output voltage of the full-wave rectifier circuit Da becomes the primary side rectified voltage Vinr which is a full-wave rectified waveform. A high-frequency component removing capacitor C3 is provided on the output side of the full-wave rectifier circuit Da. The capacitor C3 has a frequency considerably higher than the fundamental wave frequency (100 Hz in this example) of the full-wave rectified waveform. The primary rectified voltage Vinr has almost the same waveform as the full-wave rectified voltage waveform even if the capacitor C3 is provided. Here, the waveform of the primary side rectified voltage Vinr is shown in FIG.

  The primary side rectified voltage Vinr is applied to a series circuit of a parallel circuit including the switching element Q1 and the first rectifying / smoothing circuit 111 and the primary winding N1 of the transformer T. The switching element Q1 is PWM-controlled by the switching control IC 114. The switching control IC 114 controls the on-duty ratio of the switching element Q1 with a constant switching frequency (for example, 70 kHz).

  In the boost converter unit 101, during the ON period of the switching element Q1, current does not flow through the second rectifying / smoothing circuit but current flows through the switching element Q1, and the primary winding N1 is excited. A reverse bias voltage is always applied to the diode D1, and the smoothing capacitor C1 is discharged. During the OFF period of the switching element Q1, the input voltage and the energy excited in the primary winding N1 are released through the diode D1, a current flows through the second rectifying and smoothing circuit, and the smoothing capacitor C1 is charged. The

In the flyback converter unit 102, the diode D2 is turned off during the ON period of the switching element Q1, and a current flows through the primary winding N1 to excite the primary winding N1. During the OFF period of the switching element Q1, the diode D2 conducts and the excitation energy of the primary winding N1 of the transformer T is released from the secondary winding N2. That is, during the OFF period of the switching element Q1, a forward bias voltage is applied to the diode D2, and the capacitor C2 is charged. Since the reverse bias voltage is applied to the diode D2 during the ON period of the switching element Q1, the capacitor C2 is not charged but discharged.
JP-A-8-298769

  In the switching power supply device 100 disclosed in Patent Document 1, the boost converter unit 101 is used as a main power source, and the flyback converter unit 102 is used as an auxiliary power source. Therefore, the load connected to the output terminal 122 of the flyback converter unit 102 is sufficiently smaller than the load connected to the output terminal 121 of the boost converter unit 101, and the output on the flyback converter unit 102 side is the input unit. The influence on the input current of 113 is small. Therefore, conventionally, the waveform of the input current from the commercial AC power supply does not deviate greatly from the sine wave shape, and the harmonic current does not become a problem. Accordingly, in terms of the circuit, the main focus is on stabilizing the output voltage of the boost converter unit 101, and the output voltage of the boost converter unit 101 is divided by a resistor and fed back to control the switching element Q1. ing.

  However, if the load connected to the flyback converter unit 102 becomes so large that the load connected to the boost converter unit 101 cannot be ignored, the output on the flyback converter unit 102 side gives the input current to the input unit 113. The influence becomes large, and the waveform of the input current from the commercial AC power supply may deviate greatly from the sinusoidal shape, and the harmonic current becomes a problem.

Here, the above problem will be described in detail.
When the switching element Q1 is on, energy is stored in the primary winding N1. When the switching element Q1 is turned off, the cathode potential becomes higher than the anode potential of the diode D1 of the boost converter unit 101 depending on the input / output voltage and the load condition, and the flyback converter unit 102 operates, but the boost converter The part 101 may be in a non-operating state.
Alternatively, a state in which the flyback converter unit 102 and the boost converter unit 101 operate together may occur.
Further, in the flyback converter unit 102, when the voltage generated in the secondary winding N2 is lower than the cathode voltage of the diode D2, the flyback converter unit 102 is deactivated, and only the boost converter unit 101 operates. A condition can also occur.
That is, during the period when the switching element Q1 is off, it is instantaneously: • only the boost converter unit 101 is operating • only the flyback converter unit 102 is operating • the boost converter unit 101 and the fly A state where the back converter unit 102 is operating together is mixed.

  A waveform example of the output voltage Vout1 of the boost converter unit 101 at this time is shown in FIG. In this figure, the waveform of the output voltage Va1 of the boost converter unit 101 without the capacitor C1 is indicated by a broken line. The output voltage Va1 has one cycle that is 1/2 times the commercial AC power cycle (frequency: 100 Hz).

  A period (Tn + 1 to Tn + 2) in which the output voltage Va1 of the boost converter unit 101 exceeds the voltage across the capacitor C1 is a period in which the boost converter unit 101 operates dominantly, and the boost converter unit 101 is substantially in a non-operating state. It can be said that the period (Tn to Tn + 1) during which the flyback converter unit 102 operates dominantly. Actually, both the boost converter unit 101 and the flyback converter unit 102 operate before and after the timings of Tn, Tn + 1, and Tn + 2 according to the magnitudes of loads connected to the boost converter unit 101 and the flyback converter unit 102, respectively. There is a period to be used, but since this period changes according to the load connected to each converter circuit, it cannot be clearly stated how long it will be.

  Here, FIG. 3 shows circuit current waveforms of a general boost converter unit and flyback converter unit. In the general boost converter section, current flows in both the on-period and the off-period of the switching element Q1 as shown in FIG. 3A. In the general flyback converter section, as shown in FIG. Current flows only during the ON period of Q1, and no current flows during the OFF period of switching element Q1. That is, the average value of the flowing circuit current is higher in the boost converter section than in the flyback converter section if the conditions are the same.

  Therefore, in the switching power supply device 100 disclosed in Patent Document 1 above, when the load connected to the flyback converter unit 102 is increased to the same extent as the load connected to the boost converter unit 101, the switching element Q1 Is substantially the same over one commercial power supply cycle, the input current Iin during the period (Tn + 1 to Tn + 2) in which the boost converter unit 101 operates dominantly as illustrated in FIG. In the period (Tn to Tn + 1) in which the flyback converter unit 102 operates dominantly, the change rate of the input current Iin decreases and the input current waveform is greatly distorted.

  If the average value of the input current Iin is a waveform far from a sine wave shape, it has a high harmonic component, and there is a problem that the harmonic regulation cannot be cleared.

  Therefore, the present invention provides a switching power supply that can suppress harmonic currents regardless of the load connected to each circuit, even if the switching power supply apparatus outputs a DC voltage from each of the flyback converter section and the boost converter section. An object is to provide a device and an electronic device including the device.

In order to achieve the above object, the present invention provides a primary side rectifier circuit connected to an AC power source, a transformer having a primary winding and a secondary winding, and the transformer on the output of the primary side rectifier circuit. A switching element connected in series with the primary winding of the switching element for switching the input voltage of the transformer, and a first diode connected in parallel to the switching element and outputting a first DC voltage. In a switching power supply device comprising: a rectifying / smoothing circuit; and a second rectifying / smoothing circuit that is connected to the secondary winding of the transformer and outputs a second DC voltage, rectified by the primary-side rectifying circuit It detects the current, average value of the current, and a control unit for controlling the on-duty ratio of the switching element so as to form a substantially sinusoidal were similar to the input voltage waveform, the control The on-duty ratio of the switching element is increased during a period when the cathode potential is higher than the anode potential of the first diode, and the on-duty ratio of the switching element is decreased during other periods. Yes.

  Further, the control unit of the present invention further detects the output voltage of the first rectifying and smoothing circuit, adjusts a control signal applied to the control terminal of the switching element, and makes the output voltage substantially constant. It is.

  According to another aspect of the present invention, there is provided an electronic device including the above-described switching power supply device and an inverter circuit connected to an output of the first rectifying / smoothing circuit of the switching power supply device.

  According to the present invention, the current rectified by the primary side rectifier circuit is detected, and the average value of the current is made substantially sinusoidal similar to the input voltage waveform. Even a switching power supply device that outputs a DC voltage from each of the power converter and the boost converter can suppress harmonic currents regardless of the load connected to each circuit.

  Hereinafter, a first embodiment of an electronic device and a switching power supply device of the present invention will be described. In this embodiment, the output voltage of the flyback converter unit is detected and fed back to the primary side switching control IC.

  FIG. 4 shows a circuit configuration of the power supply circuit unit of the electronic device 60 according to the first embodiment. The power supply circuit unit of the electronic device 60 includes a switching power supply device 50, an inverter circuit 52, and a converter circuit 51.

  The switching power supply device 50 includes an input unit 13 that receives an input from a commercial AC power supply. The input unit 13 includes a full-wave rectifier circuit Da, which is a primary side rectifier circuit according to the present invention, and a capacitor C3. The input unit 13 is connected to a switching circuit unit 15 including a transformer T having a primary winding N1 and a secondary winding N2, a switching element Q1, a switching control IC 14, and an input current detection resistor R1.

  The input side of the full-wave rectifier circuit Da is connected to the input terminals 23-33 of the commercial AC power supply. On the output side of the full-wave rectifier circuit Da, a capacitor C3 as a filter that cuts high-frequency components is connected in cascade. Further, one end on the output side of the full-wave rectifier circuit Da is connected to the primary winding N1 of the transformer T, and the other end is connected to the primary side ground 31. One end of the switching element Q1 is connected to the output side of the full-wave rectifier circuit Da via the primary winding N1, and the other end of the switching element Q1 is connected to the primary side ground 31. A switching control IC 14 for controlling on / off of the switching element Q1 is connected to the control terminal of the switching element Q1.

  The switching control IC 14 of the switching circuit unit 15 detects the input current Iin flowing through the primary side rectifier circuit from the voltage drop of the input current detection resistor R1, and the primary winding of the full-wave rectifier circuit Da and the transformer T. The primary side rectified voltage Vinr is detected from the connection point with N1. Further, the output voltage Vout2 of the second output terminal 22 which is the output of the flyback converter unit 2 is detected by the insulation circuit 41, and the input current Iin flowing through the primary side rectifier circuit becomes sinusoidal, and the flyback converter unit 2 The on-duty ratio of the switching element Q1 is controlled so that the average output voltage becomes constant. In order to make the input current sinusoidal, the cutoff frequency of this control circuit is set to several hundred Hz to several kHz, and becomes a cutoff frequency sufficiently lower than the switching frequency (for example, 70 kHz). Note that a general circuit configuration using a photocoupler may be used as the insulating circuit 41, and description thereof is omitted here.

  The switching power supply device 50 includes a first rectifying and smoothing circuit 11 for outputting a non-insulated DC voltage from the primary side of the transformer T. The first rectifying / smoothing circuit 11 includes a rectifying diode D1 having an anode connected to a connection point between the primary winding N1 and the switching element Q1, and a cathode connected to the first output terminal 21, and the diode. A smoothing capacitor C1 having one end connected to the cathode side of D1 and the other end connected to the primary side ground 31; The first rectifying / smoothing circuit 11, the input unit 13, and the switching circuit unit 15 constitute a boost converter unit 1.

  Further, the switching power supply device 50 includes a second rectifying and smoothing circuit 12 for outputting an insulated DC voltage from the secondary side of the transformer T. The second rectifying / smoothing circuit 12 has an anode connected to one end of the secondary winding N2, a cathode connected to the second output terminal 22, and a rectifying diode D2 connected to the cathode side of the diode D2. A smoothing capacitor C2 connected to the secondary ground 32 at the other end. The diode D2 rectifies the excitation voltage generated in the secondary winding N2 of the transformer T, and the capacitor C2 smoothes the rectified output. The second rectifying / smoothing circuit 12, the input unit 13, and the switching circuit unit 15 constitute a flyback converter unit 2.

  In the first embodiment, the reinforced insulation is not particularly applied to the inverter circuit 52 connected to the output terminal of the flyback converter unit 2 that is reinforced. On the other hand, reinforced insulation is provided between the primary and secondary sides of the converter circuit 51 connected to the output terminal of the boost converter unit 1. In this way, first and second insulation outputs are obtained.

  As described above, in this embodiment, the electronic device 60 and the switching power supply device 50 are configured.

  Next, operations of the electronic device 60 and the switching power supply device 50 will be described.

  In the electronic device 60 and the switching power supply device 50, the input voltage Vin is an AC voltage of a commercial AC power supply (for example, 100V, 50Hz), and the voltage is input to the full-wave rectifier circuit Da. The output voltage of the full-wave rectifier circuit Da becomes the primary side rectified voltage Vinr which is a full-wave rectified waveform. A high-frequency component removing capacitor C3 is provided on the output side of the full-wave rectifier circuit Da. This capacitor C3 has a frequency component that is considerably higher than the fundamental wave frequency (100 Hz in this example) of the full-wave rectified waveform. Even if the capacitor C3 is provided, the primary side rectified voltage Vinr has almost the same waveform as the full-wave rectified voltage waveform. Here, the waveform of the primary side rectified voltage Vinr is shown in FIG.

  The primary side rectified voltage Vinr is applied to a parallel circuit composed of the switching element Q1 and the first rectifying / smoothing circuit 11, and a series circuit of the primary winding N1 of the transformer T and the resistor R1. On / off of the switching element Q1 is PWM-controlled by the switching control IC 14. The switching control IC 14 keeps the switching frequency constant (for example, 70 kHz) and controls the on-duty ratio of the switching element Q1.

  In the flyback converter unit 2, the diode D2 is turned off during the ON period of the switching element Q1, and a current flows through the primary winding N1 to excite the primary winding N1. During the OFF period of the switching element Q1, the diode D2 conducts and the excitation energy of the primary winding N1 of the transformer T is released from the secondary winding N2. That is, during the OFF period of the switching element Q1, a forward bias voltage is applied to the diode D2, and the capacitor C2 is charged. Since the reverse bias voltage is applied to the diode D2 during the ON period of the switching element Q1, the capacitor C2 is not charged but discharged.

  On the other hand, in the boost converter unit 1, during the ON period of the switching element Q1, no current flows through the second rectifying / smoothing circuit, current flows through the switching element Q1, and the primary winding N1 is excited. A reverse bias voltage is always applied to the diode D1, and the smoothing capacitor C1 is discharged. During the OFF period of the switching element Q1, the input voltage and the energy excited in the primary winding N1 are released through the diode D1, a current flows through the second rectifying and smoothing circuit, and the smoothing capacitor C1 is charged. The

The above operation will be described in more detail. When the switching element Q1 is on, energy is stored in the primary winding N1.
When the switching element Q1 is turned off, the cathode potential becomes higher than the anode potential of the diode D1 of the boost converter unit 1 depending on the input / output voltage and the load condition, and the flyback converter unit 2 operates, but the boost converter The part 1 may be in a non-operating state.
Alternatively, a state where both the flyback converter unit 2 and the boost converter unit 1 operate may occur.
Furthermore, when the voltage generated in the secondary winding N2 in the flyback converter unit 2 is lower than the cathode voltage of the diode D2, the flyback converter unit 2 is inoperative, and only the boost converter unit 1 is operated. A condition can also occur.
That is, during the period when the switching element Q1 is off, it is instantaneously: • only the boost converter unit 1 is operating • only the flyback converter unit 2 is operating • the boost converter unit 1 and the fly The state where the back converter unit 2 is operating together is mixed.

  FIG. 5B shows a waveform example of the output voltage Vout1 of the boost converter unit 1 at this time. In this figure, the waveform of the output voltage Va1 of the boost converter unit 1 without the capacitor C1 is indicated by a broken line. One cycle of the output voltage Va1 is ½ times the frequency of the commercial AC power supply (frequency: 100 Hz).

  A period (Tn + 1 to Tn + 2) in which the output voltage Va1 of the boost converter unit 1 exceeds the voltage across the capacitor C1 is a period in which the boost converter unit 1 operates dominantly, and the boost converter unit 1 is substantially in a non-operating state. It can be said that the period (Tn to Tn + 1) during which the flyback converter unit 2 operates dominantly. Actually, both boost converter unit 1 and flyback converter unit 2 operate before and after the timings of Tn, Tn + 1, and Tn + 2 according to the magnitude of the load connected to each of boost converter unit 1 and flyback converter unit 2. There is a period to be used, but since this period changes according to the load connected to each converter circuit, it cannot be clearly stated how long it will be.

In the present embodiment, the input current Iin is detected by the resistor R1 provided in the input current path of the switching circuit unit 15, and the switching element Q1 is set so that the input current Iin has a sine wave shape in phase with the primary side rectified voltage Vinr. By controlling the on-duty ratio, the average value of the input current Iin is made substantially sinusoidal similar to the input voltage waveform, as shown by the solid line in FIG. Specifically, the period (Tn to Tn + 1) in which the flyback converter unit 2 operates dominantly increases the on-duty ratio (the Duty2 (t)) of Q1, and the boost converter unit 1 operates dominantly. For (Tn + 1 to Tn + 2), the on-duty ratio (Duty2 (t)) of Q1 is lowered.
Note that, since the switching element Q1 is actually switched at the switching frequency (for example, 70 kHz), the instantaneous value of the current also fluctuates at that frequency, but becomes a sine wave by the capacitor C3 in FIG.

  Here, the configuration of the switching control IC 14 is shown in FIG. A voltage obtained by dividing the output voltage Vout2 of the flyback converter unit 2 is input to the inverting input terminal of the error amplifier 43A, compared with the reference voltage Vo input to the non-inverting input terminal of the error amplifier 43A, and the difference is amplified. The feedback signal is input to the multiplier 44 of the switching control IC 14 via the insulating circuit 41. The amplitude of the primary rectified voltage Vinr signal input to the multiplier 44 is changed by the output signal of the error amplifier 43A. The output of the multiplier 44 is input to the inverting input terminal of the error amplifier 43B, and is input to the non-inverting input terminal of the error amplifier 43B (R1 × Iin; detected input current Iin flowing through the resistor R1 as a voltage). And the difference is amplified. The output signal of the error amplifier 43B is input to the PWM circuit. An oscillator 46 is connected to the PWM circuit 45. The output signal of the PWM circuit 45 is input to the gate terminal of the switching element Q1 through the amplifier 47.

The PWM circuit 45 has a circuit configuration including, for example, an RS flip-flop. The PWM circuit 45 compares the sawtooth wave based on the output signal of the oscillator 46 with the control signal based on the output signal of the error amplifier 43B. The pulse width of the signal is in accordance with the output of the error amplifier 43B. This switching control IC 14 controls the on-duty ratio of the switching element Q1 according to the average value of the input current Iin in the same phase as the primary side rectified voltage Vinr.
However, feedback control from the insulating circuit 41 at this time has a cutoff frequency (several hundred Hz to several kHz) characteristic close to the commercial AC power supply frequency, and is very small with respect to the oscillation frequency (for example, 70 kHz).
With such a configuration, the average value of the input current Iin becomes a sine wave in phase with the voltage waveform of the primary side rectified voltage Vinr as shown by the solid line in FIG. For the load that requires reinforced insulation between the primary and secondary in the power supply device 50, power is supplied from the flyback converter unit, and in the power supply device 50 between the primary and secondary By supplying power from an efficient boost converter unit to a load that does not require reinforced insulation, a plurality of DC outputs can be efficiently obtained as a whole.

  In the present embodiment, the switching circuit unit 15 is provided with the resistor R1 and the input current is detected from the voltage drop. However, the input current can be detected from any position as long as the input current can be detected or estimated. In addition, the circuit configuration therefor is not limited to the resistor R1, and can be implemented in any way as long as it does not violate the idea of the present invention.

  Further, although the converter circuit 51 is provided at the output of the first rectifying / smoothing circuit 11 and the inverter circuit 52 is provided at the output of the second rectifying / smoothing circuit, the converter circuit 51 and the inverter circuit 52 are not necessarily included in the present invention. The present invention can be suitably implemented regardless of the equipment that is not an essential component and is connected to the first and second rectifying and smoothing circuits.

  Further, as shown in FIG. 7, the voltage detection circuit may be provided not on the flyback converter unit 2 side but on the boost converter unit 1 side.

  In this way, the average value of the input current Iin becomes a sine wave having the same phase as the voltage waveform of the primary side rectified voltage Vinr, and the switching power supply 50 controls the primary power supply 50 while suppressing the harmonic current. Power is supplied from the flyback converter for loads that require reinforced insulation between the secondary, and power is supplied from the efficient boost converter for loads that do not require reinforced insulation between the primary and secondary. By supplying, a plurality of direct current outputs can be efficiently obtained as a whole.

It is a figure explaining the circuit of the conventional switching power supply device. It is a wave form chart of input current and output voltage in the conventional switching power supply device. It is a waveform diagram of an input current in a general converter circuit. It is a circuit diagram of a part of the switching power supply device and the electronic device of the first embodiment. It is a figure which shows the voltage waveform and current waveform in the switching power supply device of 1st Embodiment. FIG. 3 is a circuit diagram of a switching control IC in the switching power supply device of the first embodiment. It is a circuit diagram of the switching power supply device of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101-Boost converter part 2,102-Flyback converter part 11,12,111,112-Rectification smoothing circuit 13,113-Input part 14,114-IC for switching control
15, 115—Switching circuit sections 21, 22, 121, 122—Output terminals 23, 33, 123, 133—Commercial AC power input terminal 31, 131—Primary ground 32, 132—Secondary ground 41—Insulation circuit 42-voltage detection circuit 43A, 43B-error amplifier 44-multiplier 45-PWM circuit 46-oscillator 47-buffer amplifier 50, 100-switching power supply device 51-converter circuit 52-inverter circuit 60-electronic device Da-full wave rectification Circuit Q1-switching element R1-resistances C1, C2, C3-capacitors D1, D2-diode T-transformer N1-1 primary winding N2-2 secondary winding Iin-input current Vin-input voltage Vinr-primary side rectified voltage Vout1, Vout2-Output voltage Duty1, Duty2-On duty ratio

Claims (3)

A primary side rectifier circuit connected to an AC power source, a transformer having a primary winding and a secondary winding, and an output of the primary side rectifier circuit connected in series together with the primary winding of the transformer, A switching element for switching an input voltage of the transformer; a first rectifying / smoothing circuit including a first diode connected in parallel to the switching element and outputting a first DC voltage; and a secondary winding of the transformer And a second rectifying / smoothing circuit that outputs a second DC voltage connected to the switching power supply,
A controller that detects a current rectified by the primary side rectifier circuit and controls an on-duty ratio of the switching element so that an average value of the current forms a substantially sinusoidal shape similar to an input voltage waveform ;
The control unit increases the on-duty ratio of the switching element during a period when the cathode potential is higher than the anode potential of the first diode, and decreases the on-duty ratio of the switching element during other periods.
Switching power supply.   The switching power supply device according to claim 1, wherein the control unit further detects an output voltage of the first rectifying and smoothing circuit and makes the output voltage substantially constant.   An electronic device comprising: the switching power supply device according to claim 1 or 2; and an inverter circuit connected to an output of the first rectifying / smoothing circuit of the switching power supply device.

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