JP3395857B2 - Power factor improvement circuit of switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power factor correction circuit for a switching power supply device for the purpose of improving power factor and suppressing harmonic current.

[0002]

2. Description of the Related Art Generally, a switching power supply device of this type is configured such that a series circuit of an inverter transformer primary winding and a switching device is connected to an output terminal of a rectifying circuit for rectifying an AC power supply voltage to switch the switching device. By so doing, a voltage proportional to the primary winding is induced from the secondary winding of the inverter transformer.However, when a capacitor input type rectifier circuit is used, the AC input voltage Since the current is supplied only during the high period, the input current with a large peak value is taken in near the maximum value of the AC input voltage, and as a result, the harmonic current exceeding the standard is generated in the input current. Power factor is significantly reduced. For the purpose of suppressing the harmonic current and improving the power factor, there is conventionally known one in which a step-up chopper circuit is added to the input side of a DC / DC converter as disclosed in Japanese Patent Laid-Open No. 2-155476. Although it is
Such a step-up chopper circuit requires switching means and a control IC in addition to the main switching element.
The circuit configuration becomes complicated, and it is impossible to reduce the size and cost of the device. On the other hand, Japanese Patent Laid-Open No. 5-1
In Japanese Patent No. 03468, a capacitor charging / discharging circuit is provided in the primary winding of an inverter transformer divided into two, and energy storage means for storing energy when a switching element is turned on is provided by a gap in the core of the inverter transformer or a choke coil. Thus, there is disclosed a switching power supply device capable of suppressing a harmonic current and improving a power factor with a simple configuration without adding a switch unit or a control IC.

[0003]

In the method of the prior art which does not use the step-up chopper circuit, the DC input voltage from the diode bridge circuit as the rectifying circuit is more than the inter-terminal voltage of the capacitors forming the capacitor charging / discharging circuit. When it becomes higher, one of the primary windings of the inverter transformer is induced during the OFF period of the switching element to charge the capacitor. Therefore, if an existing DC / DC converter is to be provided with a power factor correction circuit including this capacitor charging / discharging circuit and energy storage means, another primary winding must be wound around the inverter transformer in order to charge the capacitor. However, since a plurality of primary windings are incorporated in one inverter transformer, the size of the inverter transformer becomes large, and it becomes impossible to reduce the size of the entire device.

In view of the above problems, it is an object of the present invention to provide a power factor correction circuit for a switching power supply device which can be incorporated in the device with an extremely simple circuit configuration without increasing the size of the inverter transformer. And

[0005]

A power factor correction circuit of the present invention is a switching power supply in which a series circuit of an inverter transformer primary winding and a switching element is connected to an output terminal of a rectification circuit for rectifying an AC power supply voltage. In the device, a transformer in which a primary winding is inserted and connected between the primary winding of the inverter transformer and the switching element, energy storage means for storing energy from the transformer when the switching element is in conduction, and energy storage And a capacitor charging / discharging circuit having a capacitor for storing energy supplied from the transformer.
When the output terminal voltage of the rectifier circuit becomes lower than the terminal voltage of the capacitor by adjusting the turns ratio of the secondary winding to the primary winding, the discharge current from the capacitor is supplied to the primary winding of the inverter transformer. it is obtained by forming the <br/> capacitor charge and discharge circuit for supplying. In this case, the energy storage means is constituted by a gap provided in the core of the transformer, and the capacitor charging / discharging circuit connects the anode of the first diode to one end of the secondary winding of the transformer, Connecting the capacitor between the cathode of the diode and the minus output terminal of the rectifier circuit, and connecting the anode of the second diode to the connection point between the capacitor and the first diode, It is preferable that the cathode of is connected to the positive side output terminal of the rectifier circuit. The energy storage means is composed of a choke coil, and the capacitor charging / discharging circuit connects the anodes of a pair of first diodes to both ends of the secondary winding of the transformer. One end of the choke coil is connected to the connection point, the capacitor is connected between the other end of the choke coil and the minus side output terminal of the rectifier circuit, and a second connection point is provided between the capacitor and the choke coil. It is preferable that the anode of the diode is connected and the cathode of the second diode is connected to the positive side output terminal of the rectifier circuit.

[0006]

With the above construction, when the switching element is conducting, energy is stored in the energy storage means via the transformer, and when the switching element is off, the capacitor is charged by the energy stored in the energy storage means. Turn ratio of the secondary winding to the primary winding of the transformer
If the voltage between the output terminals of the rectifier circuit is adjusted and is lower than the voltage between the terminals of the capacitor, the discharge current of the capacitor is supplied to the primary winding of the inverter transformer. In this case, the capacitor is charged via a transformer separate from the inverter transformer. Therefore, when the power factor correction circuit is incorporated in the existing DC / DC converter, it is not necessary to wind another winding around the inverter transformer, and the size is not increased.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 are flyback type DC /
1 shows a first embodiment of the present invention using a DC converter. In FIG. 1, 1 is a commercial power source, 2 is a rectifier circuit such as a diode bridge for rectifying an AC power source voltage from the commercial power source 1, At the output terminals + V and -V,
An inverter composed of a series circuit of a primary winding 3A of the inverter transformer 3 and a transistor 4 as a switching element is connected. Also, the output terminals of the rectifier circuit + V, -V
A smoothing capacitor 5 having a small capacity of about 10 μF is connected to the. The non-dot side terminal of the secondary winding 3B of the inverter transformer 3 is connected to the anode of the rectifying diode 7 that constitutes the rectifying and smoothing circuit 6, and the cathode of this rectifying diode 7 and the dot side terminal of the secondary winding 3A are connected. The smoothing capacitor 8 is connected between the two. A control circuit 9 supplies a drive signal to the base of the transistor 4. By switching the transistor 4 by the control circuit 9, the DC input voltage Vi is intermittently applied to the primary winding 3A of the inverter transformer 3. Then, the DC output voltage Vo is output from both ends of the smoothing capacitor 8.

On the other hand, the primary winding 3 of the inverter transformer 3
A transformer 11 separate from the inverter transformer 3 is provided on the A side.
A power factor correction circuit 12 having is provided. The primary winding 11A of the transformer 11 is inserted and connected between the primary winding 3A of the inverter transformer 3 and the collector of the transistor, and energy is stored in the transformer 11 so that energy can be stored when the transistor 4 is turned on. As a result, a gap is provided in the core (not shown). Also transformer
The dot side terminal of the primary winding 11A of 11 is connected to the primary winding 3A of the inverter transformer 3, and the dot side terminal of the secondary winding 11B is connected to the negative side output terminal -V of the rectifier circuit 2. Reference numeral 13 is a capacitor that stores the energy supplied from the secondary winding 11B of the transformer 11, and this capacitor 13 and the first diode 14 and the second diode 15 cause a difference between the output terminals + V and -V of the rectifier circuit 2. When the voltage becomes lower than the voltage across the terminals of the capacitor 13, the capacitor charging / discharging circuit 16 is configured to supply the discharging current from the capacitor 13 to the primary winding 3A of the inverter transformer 3. The capacitor charging / discharging circuit 16 of the present embodiment includes a secondary winding 11B of the transformer 11.
Connect the anode of the first diode 14 to one end of
The capacitor 13 is connected between the cathode of the diode 14 and the negative output terminal -V of the rectifier circuit 2,
The second diode 15 at the connection point between the first diode 14 and
Of the second diode 15 is connected to the positive side output terminal + V of the rectifier circuit 2. The voltage across the terminals of the capacitor 13 is the primary winding of the transformer 11 .
It can be appropriately changed by adjusting the winding ratio of the secondary winding 11B to the wire 11A .

Next, the operation of the above structure will be described. When the power is turned on, the AC power supply voltage from the commercial power supply 1 is full-wave rectified by the rectifier circuit 2, but when the voltage between the output terminals + V and -V of the rectifier circuit 2 is higher than the voltage between the terminals of the capacitor 13, The second diode 15 becomes non-conductive, and the input current I1 from the commercial power supply 1 is switched by the transistor 4 so that the primary winding 3 of the inverter transformer 3
Flows through A intermittently. At this time, the inverter transformer 3 stores energy by the input current I1 flowing through the primary winding 3A during the ON period of the transistor 4, and the diode 7 is generated by the counter electromotive force generated in the secondary winding 3B during the OFF period of the transistor 4. Power is supplied to the smoothing capacitor 8 side via the. Further, during the ON period of the transistor 4, the input current I1 also flows through the primary winding 11A of the transformer 11, and energy is stored in the transformer 11 having a gap in the core. After that, when the transistor 4 is turned off,
This time, the counter electromotive force is generated in the secondary winding 11B by the energy accumulated in the transformer 11, and the capacitor 13 is charged via the first diode 14.

On the other hand, when the voltage between the output terminals + V and -V of the rectifier circuit 2 is lower than the voltage between the terminals of the capacitor 13, the second diode 15 becomes conductive, and the energy stored in the capacitor 13 until then. But transistor 4
Due to the switching, the discharge current I2 intermittently flows from the second diode 15 to the primary winding 3A of the inverter transformer 3. Inverter transformer 3 is transistor 4
Energy is stored by the discharge current I2 flowing through the primary winding 3A during the ON period of, and counter electromotive force generated in the secondary winding 3B during the OFF period of the transistor 4 causes power to be supplied to the smoothing capacitor 8 side through the diode 7. Supply.

FIG. 2 shows the output terminals + V and -V of the rectifier circuit 2.
It shows the DC input voltage Vi between them. As is clear from the figure, when the voltage between the output terminals + V and -V of the rectifier circuit 2 becomes lower than the voltage between the terminals of the capacitor 13, the second diode 15 becomes conductive, so that the output terminal of the rectifier circuit 2 becomes conductive. The voltage across the terminals of the capacitor 13 is applied as the DC input voltage Vi between the primary winding 3A of the inverter transformer 3 and the transistor 4 so as to fill the valley of the voltage generated between + V and -V. This makes it possible to prevent harmonic current from being generated in the input line from the commercial power supply 1 to the power supply device, and improve the power factor.

As described above, in the above embodiment, according to the first aspect, the primary winding 3A of the inverter transformer 3 and the transistor 4 are connected to the output terminals + V and -V of the rectifying circuit 2 for rectifying the AC power supply voltage. In a switching power supply device in which a series circuit is connected, a primary winding 11A is inserted and connected between a primary winding 3A of an inverter transformer 3 and a transistor 4, and a transformer 11 that stores energy when the transistor 4 is conductive, and this transformer. A capacitor charging / discharging circuit 16 having a capacitor 13 for storing energy supplied from 11
And a secondary winding for the primary winding 11A of the transformer 11.
Adjust the turns ratio of wire 11B to adjust the output terminal of rectifier circuit 2 +
V, -V voltage constitutes a capacitor charge and discharge circuit 16 for supplying a discharge current from the primary winding 3A in the capacitor 13 of the inverter transformer 3. When lower than the terminal voltage of the capacitor 13. In this case, since the transformer 13 separate from the inverter transformer 3 is used to charge the capacitor 13, the power factor correction circuit 12 as in the conventional case is used.
It is not necessary to wind another winding around the inverter transformer 3 when assembling into the existing DC / DC converter. Therefore, the power factor correction circuit 12 of the present embodiment can prevent the inverter transformer 3 from increasing in size, and can be incorporated in the device with an extremely simple circuit configuration.

Further, in this embodiment, in accordance with claim 2,
The energy storage means is composed of a gap provided in the core of the transformer 11, and the capacitor charging / discharging circuit 16
Is the first diode at one end of the secondary winding 11B of the transformer 11.
The anode of 14 is connected, and the capacitor 13 is connected between the cathode of the first diode 14 and the negative output terminal -V of the rectifier circuit 2. This capacitor 13 and the first diode 14
Connect the anode of the second diode 15 to the connection point with
The cathode of the second diode 15 is connected to the positive side output terminal + V of the rectifier circuit 2. Therefore, in this case, by using the gap of the core of the transformer 11,
Since the capacitor charging / discharging circuit 16 can be configured by the individual capacitors 13 and the two diodes 14 and 15, it is possible to prevent the inverter transformer 3 from increasing in size and to be incorporated in the device with an extremely simple circuit configuration.

This embodiment has been described by taking the flyback converter as an example, but it is also a forward converter for sending energy from the inverter transformer 3 to the output side when the transistor 4 is conducting, or a push-pull converter. However, the above-mentioned claim 1 and claim 2
Has the same action and effect as. Further, the switching element is not limited to the transistor 4, and a MOS type FET or the like can be used.

Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description of the common parts will be omitted. In this embodiment, a forward converter is used,
The polarity of the secondary winding 3B is opposite to that of the transformer 3 of FIG. The rectifying / smoothing circuit 6 is provided with a flywheel diode 7A and a choke coil 10 in addition to the rectifying diode 6 and the smoothing capacitor 8. On the other hand, in the transformer 21 that constitutes the power factor correction circuit 12, the primary winding 21A thereof is the primary winding 3A of the transformer 3 and the transistor 4
Although it is inserted and connected between and, unlike the first embodiment,
There is no gap in the core to store energy. This energy storage means is constituted by the choke coil 22 in this embodiment. The capacitor charging / discharging circuit 16 connects the anodes of the pair of first diodes 14 and 14A to both ends of the secondary winding 21B of the transformer 21, and connects the choke coil to the connection point of the first diodes 14 and 14A.
22 is connected to one end, a capacitor 13 is connected between the other end of the choke coil 22 and the negative side output terminal -V of the rectifier circuit 2, and a second diode is connected to the connection point between the capacitor 13 and the choke coil 22. Connect the anode of 15 and connect the cathode of the second diode 15 to the positive output terminal of rectifier circuit 2 +
It is configured by connecting to V.

In the above configuration, during a period in which the voltage between the output terminals + V and -V of the rectifier circuit 2 is higher than the voltage between the terminals of the capacitor 13, the second diode 15 is non-conductive.
In this case, when the transistor 4 is conducting, the input current I1 from the commercial power supply 1 is applied to the primary winding 3 of the inverter transformer 3.
A and the primary winding 21A of the transformer 21, the energy from the secondary winding 3B of the inverter transformer 3 is stored in the choke coil 10 via the diode 7, and the energy from the secondary winding 21B of the transformer 21 is also stored. Are stored in the choke coil 22 via the first diode 14. On the other hand, when the transistor 4 is turned off, on the secondary winding 3B side of the inverter transformer 3, the energy stored in the choke coil 10 is sent to the capacitor 8 side by the flywheel diode 7A, and DC is output to the output side. The output voltage Vo is generated. In addition, the energy stored in the choke coil 22 is the first diode 14A.
Sent to the condenser 13 side by this condenser 13
The voltage across the terminals of rises.

On the other hand, in the period in which the voltage between the output terminals + V and -V of the rectifier circuit 2 is lower than the voltage between the terminals of the capacitor 13,
The second diode 15 becomes conductive, and the energy stored in the capacitor 13 until then flows from the second diode 15 to the primary winding 3A of the inverter transformer 3 as the discharge current I2. The secondary winding 3B side of the inverter transformer 3 continues to supply power to the output side by the discharge current I2 from the capacitor 13 due to the switching operation of the transistor 4. As a result, as shown in FIG.
Of the capacitor 13 is applied as the DC input voltage Vi between the primary winding 3A of the inverter transformer 3 and the transistor 4 so as to fill up the valley portion of the voltage generated between the output terminals + V and -V. . This makes it possible to prevent harmonic current from being generated in the input line from the commercial power supply 1 to the power supply device, and improve the power factor.

As described above, according to the present embodiment, the output terminal + of the rectifier circuit 2 for rectifying the AC power supply voltage corresponds to the first aspect.
In a switching power supply device in which a series circuit of a primary winding 3A of an inverter transformer 3 and a transistor 4 is connected to V and -V, a primary winding 3A of the inverter transformer 3 is provided.
Transformer 21 in which a primary winding 21A is inserted and connected between the transistor 4 and the transistor 4, and the transformer 21 when the transistor 4 is conductive.
A choke coil 22 for storing the energy from and a capacitor charging / discharging circuit 16 having a capacitor 13 for storing the energy supplied from the choke coil 22 ,
Number of turns of secondary winding 21B with respect to primary winding 21A of transformer 21
By adjusting the ratio, the capacitor for supplying a discharge current from the rectifier circuit 2 of the output terminals + V, the -V voltage is lower than the terminal voltage of the capacitor 13 the capacitor 13 to the primary winding 3A of the inverter transformer 3 The charge / discharge circuit 16 is configured. Therefore, it is not necessary to wind another winding around the inverter transformer 3 when the power factor correction circuit 12 is incorporated into the existing DC / DC converter as in the conventional case, and the power factor correction circuit 12 of the present embodiment can be used. In addition, it is possible to prevent the inverter transformer 3 from increasing in size, and at the same time, it is possible to incorporate the inverter transformer 3 into the device with an extremely simple circuit configuration. Also, the capacitor 13
The voltage between the terminals of the secondary winding to the primary winding 21A of the transformer 21
It is possible to easily adjust the winding ratio of the winding 21B.
It

Further, in this embodiment, the energy storage means is constituted by the choke coil 22 according to claim 3,
The capacitor charging / discharging circuit 16 connects the anodes of the pair of first diodes 14, 14A to both ends of the secondary winding 21B of the transformer 21, and the choke coil 22 is connected to the connection point of the cathodes of the first diodes 14, 14A. Of the second diode 15 at the connection point between the capacitor 13 and the choke coil 22. The anode is connected and the cathode of the second diode 15 is connected to the positive side output terminal + V of the rectifier circuit 2. Therefore, in this case, increase the size of the inverter transformer 3
Without using a very simple circuit configuration.
In addition, the voltage across the terminals of the capacitor 13 can be easily adjusted by the turn ratio of the secondary winding 21B to the primary winding 21A of the transformer 21.

In this embodiment as well, as in the first embodiment,
Of course, a MOS type FET can be applied as the switching element. Further, the present embodiment can be applied not only to the forward type converter but also to a flyback type converter, a push-pull type converter and the like.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

[0022]

The power factor correction circuit according to claim 1 is a switching power supply device in which a series circuit of a primary winding of an inverter transformer and a switching element is connected to an output terminal of a rectification circuit for rectifying an AC power supply voltage. In the transformer, a primary winding is inserted and connected between the primary winding of the inverter transformer and the switching element, energy storage means for storing energy from the transformer when the switching element is conductive, and the energy storage means. A capacitor with a capacitor that stores the energy supplied from
The primary winding of the transformer consists of a capacitor charging and discharging circuit.
The winding ratio of the secondary winding to the wire is adjusted, and when the voltage between the output terminals of the rectifier circuit becomes lower than the voltage between the terminals of the capacitor, the discharge current from the capacitor is supplied to the primary winding of the inverter transformer. As described above, the capacitor charging / discharging circuit is configured , and the inverter transformer can be incorporated into the device with an extremely simple circuit configuration without increasing the size of the inverter transformer. Also, between the terminals of the capacitor
Voltage can be easily adjusted by the turns ratio of the transformer
It becomes Noh.

The power factor correction circuit according to claim 2 is
The energy storage means is composed of a gap provided in the core of the transformer, and the capacitor charging / discharging circuit connects the anode of the first diode to one end of the secondary winding of the transformer, The capacitor is connected between the cathode and the negative output terminal of the rectifier circuit, the anode of the second diode is connected to the connection point between the capacitor and the first diode, and the cathode of the second diode is connected. Since it is connected to the plus side output terminal of the rectifier circuit, the inverter transformer can be incorporated in the device with an extremely simple circuit configuration without increasing the size.

The power factor correction circuit according to claim 3 is
The energy storage means is composed of a choke coil, the capacitor charging / discharging circuit connects the anodes of a pair of first diodes to both ends of the secondary winding of the transformer, and the connection point of the cathodes of the respective first diodes. Is connected to one end of the choke coil, the capacitor is connected between the other end of the choke coil and the minus side output terminal of the rectifier circuit, and a second diode is provided at a connection point between the capacitor and the choke coil. Is connected to the anode of the second diode and the cathode of the second diode is connected to the positive side output terminal of the rectifier circuit, and can be incorporated into the device with an extremely simple circuit configuration without increasing the size of the inverter transformer. At the same time, the voltage between the terminals of the capacitor can be easily adjusted by the turns ratio of the transformer.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a power supply device showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram of a DC input voltage of the same as above.

FIG. 3 is a circuit configuration diagram of a power supply device showing a second embodiment of the present invention.

[Explanation of symbols]

2 rectifier circuit 3 Inverter transformer 4 transistors (switching elements) 11 Transformer (energy storage means) 13 Capacitor 14,14A First diode 15 Second diode 16 Capacitor charge / discharge circuit 21 transformer 22 Choke coil (energy storage means)

Claims (3)

(57) [Claims] 1. A switching power supply device in which a series circuit of an inverter transformer primary winding and a switching element is connected to an output terminal of a rectifying circuit for rectifying an AC power supply voltage, wherein the inverter transformer primary winding and the switching circuit are connected. capacitors with a transformer primary winding between the element is inserted and connected, the energy storage means storing energy from said transformer during conduction of the switching element, a capacitor for storing energy supplied from the energy storage means It consists of a charge and discharge circuit
Adjust the turns ratio of the secondary winding to the primary winding of the transformer
Then, when the voltage between the output terminals of the rectifier circuit becomes lower than the voltage between the terminals of the capacitor, the discharge current from the capacitor is supplied to the primary winding of the inverter transformer.
A power factor correction circuit for a switching power supply device , wherein the capacitor charging / discharging circuit is configured as described above . 2. The energy storage means is composed of a gap provided in the core of the transformer, and the capacitor charging / discharging circuit connects an anode of a first diode to one end of a secondary winding of the transformer, The capacitor is connected between the cathode of the first diode and the negative output terminal of the rectifier circuit, and the anode of the second diode is connected to the connection point between the capacitor and the first diode. The power factor correction circuit for a switching power supply device according to claim 1, wherein the cathode of the diode is connected to the positive side output terminal of the rectifier circuit. 3. The energy storage means is composed of a choke coil, and the capacitor charging / discharging circuit has a pair of first diodes connected to the anodes of both ends of a secondary winding of the transformer. One end of the choke coil is connected to the connection point of the cathode of, and the capacitor is connected between the other end of the choke coil and the minus side output terminal of the rectifier circuit, and the connection point between the capacitor and the choke coil. 2. The power factor improvement of a switching power supply device according to claim 1, wherein the anode of the second diode is connected to and the cathode of the second diode is connected to the positive side output terminal of the rectifier circuit. circuit.