JP2001145359A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the cost of a switching power supply by lowering the current capacity of a circuit component for improving the power factor. SOLUTION: A first diode 1 is inserted in series with a snubber capacitor 17. A series circuit having a second diode 2 and a third diode 3 in which the same polarity poles are opposed and connected is connected in parallel with an AC power source 11. A reactor 4 is connected from the connecting point of the capacitor 17 to the diode 1 to the connecting point of the diode 2 to the diode 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a switching power supply, and more particularly to a switching power supply having a power factor correction circuit.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an example of a conventional system. In FIG. 2, the AC voltage of the AC power supply 11 is full-wave rectified by the bridge rectifier 12 and charges the smoothing capacitor 13 through the reactor 24 and the diode 23.
The DC voltage of the smoothing capacitor 13 is intermittently applied to the primary winding 14a of the transformer 14 as the switching element 15 is repeatedly turned on and off. The current flowing through the primary winding 14a during the ON period of the switch element 15 includes a load current for supplying power to the secondary-side load and an excitation current for exciting the core of the transformer 14, but is accumulated in the core by the excitation current. When the switching element 15 is turned off, the exciting energy flows through an annular circuit including the primary winding 14a, the capacitor 17, and the diode 23, charges the capacitor 17, and stores the energy in the form of electric charge. Switch element 15
Is turned on from the off period, the capacitor 17
Flows through a ring circuit including the switch element 15, the bridge rectifier 12, the AC power supply 11, and the reactor 24.
At this time, the AC current also flows when the absolute value of the AC voltage of the AC power supply 11 is lower than the voltage of the smoothing capacitor 13. In a general capacitor input type rectifier circuit, AC current does not flow in the section where the absolute value of the AC voltage is lower than the voltage of the smoothing capacitor, so the conduction angle of the AC current is narrowed and the power factor is reduced. In the second circuit, an alternating current flows each time the switch element 15 is turned on, so that the conduction angle is widened and the power factor is improved.

[0003]

In the circuit of FIG.
When the switch element 15 is turned on, the diode 23 stores the electric charge of the smoothing capacitor 13 in the snubber capacitor 1.
7 to prevent discharge. Further, in the reactor 24, when the switch element 15 is turned on, the flow of the electric charge of the snubber capacitor 17 becomes a resonance current flowing through a series resonance circuit including the reactor 24 and the snubber capacitor 17, and a half cycle of resonance ends in the ON period. The inductance is selected as follows. The resonance current flowing through the reactor 24 is made unidirectional by the bridge rectifier 12, and ends when the resonance current rises from zero and returns to zero if the half cycle of the resonance is shorter than the ON period.

[0004] A current for charging the smoothing capacitor 13 flows through the reactor 24 and the diode 23 in addition to a current for increasing the conduction angle of the AC current. The wire diameter of the winding of the reactor 24 needs to be large enough to allow the effective value of the alternating current, and the diode 23 needs to have the effective value of the alternating current. Therefore, neither the reactor 24 nor the diode 23 contributes to the overall cost of the switching power supply device. Also diode 2
Although the drop voltage due to 3 goes from 1 volt to 1.5 volts, a power loss occurs due to this drop voltage. Therefore, the present invention provides a reactor comprising a winding having a small wire diameter,
It is an object of the present invention to provide a power factor improving circuit using a method in which a diode having a smaller current capacity can be used and the influence of a drop voltage of the diode is smaller.

[0005]

In order to achieve the above object, the present invention provides an AC power supply, a full-wave rectifier, a smoothing capacitor, a series circuit comprising a primary winding of a transformer and a switch element, In a switching power supply device including an oscillation control circuit connected to a control electrode of an element and a snubber capacitor connected in parallel to a primary winding of a transformer, a first diode is inserted in series into the snubber capacitor and the same as each other. A series circuit of a second diode and a third diode whose electrodes are connected face-to-face is connected in parallel to an AC power supply, a connection point of the second diode and the third diode, a snubber capacitor, and a first diode The reactor was connected between the connection points.

[0006] The DC voltage of the smoothing capacitor is intermittently applied to the primary winding of the transformer by repeatedly turning on and off the switching element. The current flowing in the primary winding of the transformer during the ON period of the switch element is composed of a load current supplied to the load via the secondary winding of the transformer and an exciting current for exciting the transformer core. When the switching element is turned off, the exciting energy flows through the annular circuit including the primary winding of the transformer, the snubber capacitor, and the first diode, and stores the energy again as electric charge in the snubber capacitor.

When the turned-off switch element is turned on next time, the electric charge of the snubber capacitor is stored in an annular circuit formed by the switch element, the AC power supply, the second diode and the reactor, or the switch element, the AC power supply and the third diode. And it flows through the annular circuit made by the reactor and discharges. The discharge current at this time becomes a half-wave current resonance due to the second diode and the third diode. By selecting an appropriate value of the inductance of the reactor, the discharge current rises at zero during the ON period of the switch element and ends at zero. You can do so.

Although the current rises from zero and returns to zero again by half-wave current resonance, the snubber capacitor is charged with a voltage of the same value whose direction is inverted. The power loss that occurs at this time is only a loss due to the resistance of the line through which the current flows. Since this current flows each time the switch element is turned on, even when the absolute value of the voltage of the AC power supply is lower than the voltage of the smoothing capacitor, the conduction angle of the AC input current increases.

In addition, the current that serves to increase the conduction angle is
Since the current is separated from the current for charging the smoothing capacitor, the effective current flowing through the second diode, the third diode, and the reactor is small, and therefore, a diode having a small current capacity and a reactor having a small current capacity can be used. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to FIG. In FIG. 1, an AC power supply 11
Is supplied by the bridge rectifier 12 to be full-wave rectified, and the smoothing capacitor 13 is charged with the DC voltage. This DC voltage is intermittently applied to the primary winding 14a of the transformer 14 by the ON / OFF operation of the switch element 15. The change in magnetic flux generated in the transformer 14 due to the intermittent voltage is taken out as the intermittent voltage of the secondary winding 14b,
The DC voltage is rectified and smoothed by the diode 18 and the diode 19 and the reactor 20 and the capacitor 21 and supplied to the load 22. The switching circuit used in this embodiment is called a forward converter.

In FIG. 1, the snubber capacitor 17 repeats charging and discharging every time the switch element 15 is turned off and turned on. When the switching element 15 is turned off, the excitation energy stored in the core of the transformer 14 flows through the annular circuit formed by the primary winding 14a, the snubber capacitor 17, and the first diode 1, and the snubber capacitor 17
Charge. Then, when the switch element 15 is turned on, the switch element 15, the AC power supply 11, the bridge rectifier 12, and the second diode, or the annular circuit formed by the third diode flows to discharge.

The second diode and the third diode are O
An R diode is formed, and one of them conducts with respect to a positive or negative change of the AC voltage. Second diode or third
Irrespective of the current flowing through the bridge rectifier 12 and charging the smoothing capacitor 13, the current flows each time the switch element 15 is turned on, so that the conduction angle of the AC current of the AC power supply 11 is increased.

In the case of a capacitor input type rectifier,
The phase in which the alternating current flows is limited to approximately 60 to 120 degrees in a half cycle of 0 to 180 degrees. Although this deteriorates the power factor, in the circuit of FIG. 1, every time the switch element 15 is turned on, an alternating current flows in any phase from 0 to 180 degrees, so that the power factor is improved.

[0014]

The current that has the effect of improving the power factor is the discharge current of the snubber capacitor 17, which is generated each time the switch element is turned on, but smaller than the current flowing through the bridge rectifier 12. Therefore, the reactor constituting the annular circuit through which the current flows, the second diode and the third diode can use those having small current capacities, so that the cost can be greatly reduced as compared with the conventional system, and economic effects are expected. You.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st diode 2 2nd diode 3 3rd diode 4 Reactor 11 AC power supply 12 Bridge rectifier 13 Smoothing capacitor 14 Transformer 15 Switch element 16 Oscillation control circuit 17 Snubber capacitor 18 and 19 Diode 20 Reactor 21 Capacitor 22 Load 22 Diode 24 reactor 14a primary winding 14b secondary winding

Claims (1)

[Claims] 1. An AC power supply, a full-wave rectifier, a smoothing capacitor, a primary winding of a transformer, a switching element connected in series to the primary winding, and a control electrode of the switching element. A switching control circuit, comprising a snubber capacitor connected in parallel with the primary winding, a terminal connected to a connection point between the first winding of the snubber capacitor and the switch element. A first diode is inserted between a terminal on the other side of the first winding and a terminal on the other side of the first winding to which the switch element is connected, and the same electrodes are connected face to face. A series circuit consisting of a diode and a third diode is connected in parallel to the AC power supply, and a connection point between the snubber capacitor and the first diode, the second diode, and the third die A switching power supply device characterized in that a reactor is connected between connection points of an aode, thereby improving a power factor.