JPH04161062A - Switching power supply - Google Patents

Abstract

PURPOSE:To improve power factor of an AC power supply through a simple circuitry by providing a power factor improving circuit which connects a capacitor to the tertiary winding of a transformer. CONSTITUTION:Charge/discharge of energy to/from a capacitor 37 and an inductance 38 in a power factor improving circuit 39 is repeated in response to ON/ OFF operation of a switching element 25 subjected to PWM control thus modulating and controlling current flowing on an input voltage Vi line. The switching element 25 is turned OFF immediately after storage of energy in the capacitor 37 and the inductance 38 and turned ON immediately after discharge of energy therefrom. Consequently, the modulation factor VA/VP, which is the ratio of the maximum variation VA from the reference value VP to the reference value VP, of the input voltage Vi can be brought close to 1 and the wave-forms of voltage and current of a commercial power supply 21 are substantially matched resulting in improvement of power factor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power factor correction circuit for a switching power supply.

Conventional technology] Switching power supplies generally input DC voltage and output any voltage, but they rectify and smooth the AC source voltage from a commercial power source using a rectifying diode and a large-capacity smoothing capacitor to convert it to DC voltage. When converting to voltage, even though the power supply voltage has a perfect sine waveform, the current flows only while the smoothing capacitor is being charged and becomes a pulse waveform, causing a drop in power factor and becoming a source of high-frequency noise. Become.

In order to prevent such a drop in power factor, a step-up chopper circuit as shown in Fig. 5 has been proposed. The DC input voltage vi is applied to a first switching element 3 consisting of an FET, an inductance 4, and a diode 5.
The voltage is applied to a boost chopper circuit 6 for power factor improvement, which is a boost circuit constituted by a booster circuit, and a predetermined pulse is supplied from the control IC 7 to the switching element 3 for switching. As a result, the voltage induced in the secondary winding of the transformer 9 is rectified and smoothed by the rectifying and smoothing circuit 11, and the output terminals +V and -
DC output voltage ■ to load 12 via V. supply. Then, the DC output voltage (■) is generated by the voltage dividing resistor 13°14 connected in series between the output terminal →-V and -V. is detected and a signal is sent to the pulse width control port #115, and based on this signal, the pulse width control circuit 15 outputs the voltage ■. The switching element 10 is subjected to PWM control so as to keep it constant. In this case, when the switching element 3 is on, the current from the input rectifier circuit 2 flows through the switching element 3 and electromagnetic energy is stored in the inductance 4, and when the switching element 3 is off, the electromagnetic energy stored in the inductance 4 and the input A boosted DC input voltage is output by superimposing the current from the rectifier circuit 2 and rectifying and smoothing it using a diode 5 and a capacitor 8, and the DC input voltage Vi has a waveform as shown in FIG. After the current flowing through the diode 5 becomes zero, the switching element 3 is turned on again, and the DC input voltage i is modulated by dividing the maximum change vA from the reference value P by the reference value V. Since it is possible to bring the degree V A / V p close to 1, and there is no need to connect a large capacity capacitor to the output terminal of the input rectifier circuit 2, the AC voltage waveform and current waveform of the commercial power supply 1 can be almost matched. This makes it possible to improve the power factor.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, the boost chopper circuit 6 for improving the power factor of the AC power source controls the switching element 3 by the control IC 7. The switching element 3 and the control IC 7 for controlling the switching element 3 are additionally required, which complicates the circuit configuration and makes it impossible to downsize and reduce the cost of the switching power supply. Ta.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a switching power supply device that can improve the power factor of an AC power supply with a simple circuit configuration without using a switching element or an IC for controlling the switching element.

"Means for Solving the Problems" The present invention switches a DC input voltage obtained by rectifying an AC power supply voltage by a switching element connected in series with the primary winding of a transformer, and converts the voltage induced in the secondary winding of the transformer. In a switching power supply that outputs a rectified and smoothed signal and controls the switching element on and off using a drive signal based on the output via a feedback loop, a tertiary winding is wound around the transformer, and a current flows from the tertiary winding of the transformer. The power factor correction circuit includes a capacitor connected to the tertiary winding of the transformer, which charges when the current is supplied and supplies a discharge current to the DC input voltage line when the current is no longer supplied.

[Function] With the above configuration, a current flows to the capacitor based on the voltage induced in the tertiary winding of the transformer by the power factor correction circuit, and the capacitor is charged. When the current flowing to the capacitor is no longer supplied, the charging energy of the capacitor is lost. The discharge current is supplied to the DC input voltage line, and as a result, the voltage waveform and current waveform of the AC input power source substantially match, improving the power factor.

[Example code] Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a forward-type switching power supply device showing a first embodiment of the present invention, in which a commercial power supply 21 is rectified by an input rectifier circuit 22, and the rectified DC input voltage ■i is transmitted by a small-capacity smoothing capacitor 23. By smoothing the voltage induced in the secondary winding S of the transformer 24 by switching it with the switching element 25 consisting of an FET connected in series to the primary winding P of the transformer 24, the voltage is passed through the rectifier diodes 26, 27, the inductance 28 and Smoothing capacitor 2
The DC output voltage Vo is rectified and smoothed by 9 and supplied to the load 30 via output terminals 10V and -V. DC output voltage■.

is divided by the resistors 31 and 32 and applied to the pulse width control circuit @33 as an output detection voltage, and based on this output detection voltage, the pulse width control circuit 33 outputs the switching element 2.
5 to turn on the switching element 25.
Control off.

On the other hand, a tertiary winding W is wound around the transformer 24, and an anode of a diode 34 is connected to one end of the tertiary winding W, and a diode 3 is connected to the cathode of the diode 34.
5, and the anode of this diode 35 and the other end of the tertiary winding W are connected to the ground line of the input voltage Vi. A series circuit of a diode 36 and a polarized electrolytic capacitor 37 is inserted between the output terminals of the input rectifier circuit 22 by connecting the anode of the diode 36 and the positive side of the capacitor 37. # connection point with and diode 34
．． A power factor correction circuit 39 is configured by inserting and connecting an inductance 38 between the connection point 35 and the connection point 35. t
The transformer 24 has an auxiliary winding wound thereon, and a diode 40 is connected between the auxiliary winding and the ground line of the input voltage Vi.
is inserted and connected, and this auxiliary winding and diode 4
0 is for returning the excitation energy of the transformer 24 to the capacitor 23, thereby preventing saturation of the transformer 24.

Next, the operation of the above configuration will be explained.

When the power is turned on, the AC power supply voltage from the commercial power supply 21 is rectified by the input rectifier circuit 22, and this rectified input voltage V
i is the primary winding P of the transformer 24 via the capacitor 23
is applied to and is switched by controlling the switching element 25 to turn on and off. When this switching element 25 is on, the input voltage v is applied to the primary winding P of the transformer 24.
1 is applied, the voltage induced in the secondary winding S flows through the diode 26, the inductance 28 and the capacitor 2.
9, the current flows from the tertiary winding W to the capacitor 37 via the diode 34 and the inductance 38 due to the voltage induced in the tertiary winding W.
Capacitor 37 is charged.

Next, when the switching element 25 is off, the secondary winding S
The electromagnetic energy stored in the inductance 28 on the side is released, and current flows from the inductance 28 to the diode 27 via the load 30 together with the discharge current of the capacitor 29, and in this way, the switching element 2
5 is turned on and off, the output voltage v0 is supplied to the load 30, and the output voltage v0 is divided by the resistors 31 and 32 and applied to the pulse width control circuit 33 as an output detection voltage. So-called PWM control is performed to control the switching time of the switching element 25 so as to maintain the output voltage v0 at a predetermined constant voltage.

On the other hand, on the tertiary winding W side, since the input voltage Vt is no longer applied to the primary winding of the transformer 24, no voltage is induced in the tertiary winding W. Therefore, when the switching element 25 is turned on, the charging energy of the capacitor 37 stored in the capacitor 37 is released, and a current flows through the diode 36 to the input voltage vl line. At the same time, the electromagnetic energy of the inductance 38 is also released, and the current flows from the diode 35 to The input voltage vimi line flows through the inductance 38 and the diode 36.

Therefore, energy is accumulated in the capacitor 37 and the inductance 38 in the power factor correction circuit 39 in accordance with the on/off operation of the switching element 25 which is PWM controlled based on the drive signal output from the pulse width control circuit #I33. The discharge is repeated and the current to the input voltage v1 line is modulated and controlled. In this case, capacitor 37
At the same time as the storage of energy in the inductance 38 is completed, the switching element 25 is turned off, and at the same time as the energy is discharged, it is turned on, and the input voltage V in FIG.
i is the maximum change from the reference value V, and e is the reference value V2
It is possible to bring the modulation factor A/vP, which is divided by Generation of high frequency noise can be suppressed.

In this embodiment, the transformer 24 is provided with the tertiary winding W, and when the switching element 25 is turned on, charging is performed when current is supplied from the secondary winding @W, and when the switching element 25 is turned off, charging is performed. The power factor can be improved by connecting the capacitor 37 to the tertiary winding W and configuring the power factor correction circuit 39, which discharges when the current is no longer supplied and supplies the input voltage ■i line current. With this, there is no need to separately provide a switching element for power factor improvement and an IC to control this switching element, and the power factor can be improved with a simple circuit configuration mainly consisting of the tertiary winding W and the capacitor 37. It is possible to reduce the size and cost of the device.

FIG. 2 shows a push-pull type switching power supply device showing a second embodiment of the present invention, and the same parts as in FIG.

In this embodiment, the primary winding P of the transformer 24A,
, P2 are connected to push-pull transistors 41, 42, and a control pulse signal is alternately conducted to the base of each transistor 41, 42 to obtain an alternating current voltage with positive and negative symmetry. The transformer 24A is switched by the switching element 25 connected to the point via the inductance 38A.
The output voltage ■ is caused by the voltage induced in the secondary winding S0, 32 of. I'm trying to get it. In addition, the power factor correction circuit 39A connects the anode of the diode 43A to one end of the secondary winding @w, , w2 of the transformer 24A, and connects the cathode of the diode 43A to the connection point between the diode 36 and the capacitor 37.
By connecting the anode of the diode 43B to the other ends of the tertiary windings W1 and W2, and connecting the cathode of the diode 43B to the cathode of the diode 43A, a diode 43A is connected to both ends of the tertiary windings W+ and W2.
.

The capacitor 37 is connected through 43B, and the tertiary winding W,
, the center tap of W2 is connected to the connection point between the switching element 25 and the capacitor 37, the anode of the diode 44 is connected to the connection point between the inductance 38A and the switching element 25, and the cathode of the diode 44 is connected to the input voltage V.
It is configured by connecting the i-mi line.

When the switching element 25 is on, the transistor 41
and 42 are alternately conductive, so that the input voltage V
The current flowing from the i line is the primary winding P of the transformer 24A.
The inductance 38A is reached through the secondary winding P2 and the transistor 41, or through the secondary winding P2 and the transistor 42, and electromagnetic energy is stored in the inductance 38A, and the voltage induced from the secondary windings St and St of the transformer 24A flows through the diode. The output voltage is rectified and smoothed by 26.27A and a capacitor 29 to become an output voltage V0.

Next, when the switching element 25 is off, the electromagnetic energy stored in the inductance 38A is released, and the current flows from the diode 44 to the primary winding MP of the transformer 24A or - depending on the conduction state of the transistors 41 and 42.
The flow output voltage vo is supplied to the next winding P2. When the transistor 42 is in the on state regardless of whether the switching element 25 is on or off, the current from the tertiary winding W1 of the transformer 24A flows to the capacitor 37 via the diode 43A, and the capacitor 37 is charged. When transistors 41 and 42 turn off, capacitor 3
7, the charging energy of the capacitor 37 is released, and the input voltage Vi line current flows through the diode 36 to be modulated and controlled. Next, when the transistor 41 turns on, the secondary of the transformer 24A The current from the volume @ W 2 flows through the diode 43B to the capacitor 37 to charge the capacitor 37, and then when the transistors 41 and 42 turn off, the charging energy of the capacitor 37 is released and the diode 36
The input voltage Vi-line current flows through it and is modulated and controlled, and has the same operation and effect as the first embodiment.

FIG. 3 shows a flyback type switching power supply device showing a third embodiment of the present invention.The same parts as in FIG. The polarity of the secondary winding S of 24B is reversed, and the auxiliary winding is connected to diode 40 and diode 2.
The structure is the same as that in FIG. 1 except that 7 and inductance 28 are omitted.

When the switching element 25 is turned on, electromagnetic energy is stored in the primary winding P of the transformer 24B and charged to the capacitor 37, and when the switching element 25 is turned off, the stored electromagnetic energy is supplied to the secondary winding S. The output voltage v0 is obtained, and the capacitor 3
7 of the charging energy is released, and has the same action and effect as the first embodiment.

FIG. 4 shows a flyback type switching power supply device showing a fourth embodiment of the present invention.The same parts as in FIG. The polarity of the tertiary winding W of the transformer 24C is reversed and the power factor improvement diagram F! In @39B, the diode 35 and inductance 38 are omitted, and the cathode of the diode 34 is connected to the connection point between the diode 36 and the capacitor 37, but the configuration is the same as that in FIG. When the switching element 25 is off, current flows from the tertiary winding W of the transformer 24C to the capacitor 37 via the diode 34, and the capacitor 37 is charged.
When the switching element 25 is on, the capacitor 37
The charging energy is released and the discharge current flows through the diode 36.
By supplying the input voltage Vi line through the second embodiment, it has the same operation and effect as the first embodiment.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the gist of the present invention. For example, a transistor may be used as the switching element instead of an MO3 type FET, or The detection voltage obtained by dividing the output voltage may be supplied to the pulse width control circuit via a photocoupler, and the power factor correction circuit can be used with various types of switching power supplies! Applicable to

[Effects of the Invention] The present invention switches a DC input voltage obtained by rectifying an AC power supply voltage by a switching element connected in series to the primary winding of the transformer, and rectifies and smoothes the voltage induced in the secondary winding of the transformer. In a switching power supply that outputs an output and controls on/off the switching element by a drive signal based on the output via a feedback loop, a tertiary winding is wound around the transformer, and current is supplied from the tertiary winding of the transformer. The switching element and this switching element are equipped with a power factor correction circuit that connects a capacitor to the tertiary winding of the transformer, which charges the current when the current is no longer supplied, and discharges the current to the DC input voltage line when the current is no longer supplied. It is possible to provide a switching power supply device that can improve the power factor of an AC power supply with a simple circuit configuration without using an IC to control the

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a first embodiment of the present invention, Fig. 2 is a circuit diagram showing a second embodiment of the invention, and Fig. 3 is a circuit diagram showing a third embodiment of the invention. , FIG. 4 is a circuit configuration diagram showing a fourth embodiment of the present invention, FIG. 5 is a circuit configuration diagram showing a conventional example, and FIG. 6 is a waveform diagram showing the degree of modulation of input voltage. 21...Commercial power supply 22...Input rectifier circuit 24.24A, 24B, 24C...Transformer 25...
・Switching element 37...Capacitor 39, 39A, 39B...Power factor correction circuit W...Tertiary winding

Claims (1)

[Claims] The DC input voltage obtained by rectifying the AC power supply voltage is switched by a switching element connected in series to the primary winding of the transformer, and the voltage induced in the secondary winding of the transformer is rectified and smoothed and output, and then passed through a feedback loop. In a switching power supply device that controls on/off of the switching element by a drive signal based on an output, a tertiary winding is wound around the transformer, and charging is performed when current is supplied from the tertiary winding of the transformer, A switching power supply device comprising a power factor correction circuit in which a capacitor is connected to a tertiary winding of the transformer to supply a discharge current to a DC input voltage line when current is no longer supplied.