JP2002218753A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply flyback converters to a high-output power supply, by reducing ripple components contained in the input current and the output current of the flyback converters. SOLUTION: A second flyback converter, which shares a primary-side smoothing capacitor and a secondary-side smoothing capacitor of a first flyback converter, between the second flyback converter and the first flyback converter, is connected in parallel. A second switching element 2 of the second flyback converter is driven by an alternating-current signal produced at a tertiary winding 12c of a first transformer 12 of the first flyback converter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a switching power supply, and more particularly to a technique for reducing a ripple component contained in an input current and an output current.

[0002]

2. Description of the Related Art Conventionally, a method called a half bridge or a full bridge has been used as means for reducing a ripple component of an input current and an output current of a switching power supply.

FIG. 5 shows a principle diagram of a half bridge. However, the two switch elements 13a and 13b are alternately turned on and off alternately, and the two switch elements are not simultaneously turned on. When the switch element 13a is on, the current supplied from the DC power supply 21 passes through the primary winding 12a of the first transformer 12 and the capacitor 20b. At this time, the current flows through the primary winding from the top to the bottom of the figure. When the switch element 13b is turned on, the current flows through the primary winding 12a.
And the capacitor 20a, but flows through the primary winding from the bottom to the top of the figure.

Although the ON periods of the switching elements 13a and 13b do not exceed 50% of the cycle, the current of the DC power supply can widen the conduction angle to nearly 100% as shown in FIG. As a result, the ripple component included in the current of the DC power supply 21 decreases. The ripple component of the current flowing from the secondary windings 12b and 12d of the transformer to the second smoothing capacitor 16 is also reduced.

[0005] By reducing the ripple component,
There is an advantage that power loss caused by the DC resistance component of the DC power supply 21 is reduced. When the DC power supply has a filter circuit including a capacitor and an inductor, the ripple current flowing through the capacitor is also reduced, so that the power loss due to the equivalent series resistance of the capacitor is also reduced. The same applies to the output current on the secondary side.

[0006]

However, the conventional method has a disadvantage that a circuit for driving the switch elements 13a and 13b is complicated.

Accordingly, the present invention provides a circuit for reducing a ripple component of an input current with a simpler circuit.

[0008]

According to the present invention, as shown in FIG. 1, a first smoothing capacitor 11 and a second smoothing capacitor 1 of a first flyback converter are used.
6 are connected in parallel, and the second switch element 2 of the second flyback converter is connected to the first transformer 12 of the first flyback converter. Based on the AC signal generated in the tertiary winding 12c, the circuit is turned on / off by a pulse generated by the circuit including the capacitor 5 and the resistor 6 having an appropriate time constant and the third switch element 4.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The on-period of a first switch element 13 which is a switch element of a first flyback converter and a second switch element 2 which is a switch element of a second flyback converter are shown in FIG. As shown in the above, the polarity of the tertiary winding 12c is selected so as to be alternated,
The capacitor 5 and the resistor 6 are selected so that the ON period of the second switch element 2 does not overlap with the ON period of the first switch element 13.

As shown in FIG. 4, the voltage of the capacitor 5 changes exponentially with respect to the voltage generated in the tertiary winding 12c. The ON period of the second switch element 2 is given by t2 in the figure. That is, when the voltage of the capacitor 5 reaches the threshold value of the control electrode of the third switch element 4, the third switch element 4 is turned on, and the second switch element 2 is turned off. Number of turns 1
By appropriately selecting the voltage of 2c and the values of the capacitor 5 and the resistor 6, the second switch element 2 can be turned off before the first switch element 13 is turned on.

[0011]

FIG. 1 is a circuit diagram showing an embodiment of the first aspect of the present invention.

In FIG. 1, a first switch element 13 repeats on / off by a pulse output from an oscillation control circuit 14, and supplies a constant DC voltage to a load 17 via a first transformer 12.

The second switch element 2 includes a first transformer 1
The on / off operation is repeated by a pulse generated in the tertiary winding 12c wound around the second switch element 2, but the on / off phase of the first switch element 13 is inverted. Further, the ON period of the second switch element 2 is limited by the third switch element 4, the capacitor 5, and the resistor 6, and is turned off before the first switch element 2 is turned on.

Since the currents flowing through the first switch element 13 and the second switch element 2 are inverted in phase and do not overlap each other, the conduction angle of the input current is widened and the ripple component is reduced. Also, on the secondary side, the first diode 1
Since the current flows alternately through 5 and the second diode 7, the conduction angle is widened and the ripple component is reduced.

In FIG. 1, the impedance element 3 may be a resistor, but may be a circuit combining a capacitor and an inductor in addition to the resistor.

In FIG. 1, MOSFETs are selected for the first switch element 13 and the second switch element 2, and bipolar transistors are selected for the third switch element 4. These are different types of switch elements. It is possible to replace it.

In FIG. 1, the oscillation control circuit 14 may have a fixed frequency or a self-excited oscillation.

FIG. 2 is a circuit diagram showing an embodiment of the second aspect of the present invention.

In FIG. 2, a circuit comprising a second transformer 1 and a second switch element 2 is connected to an AC power supply 8 via a center tap diode 9. As a result, the power factor is improved because the current flows over an angle of 360 ° of the phase of the alternating current.

[0020]

Conventionally, the range of power to which the flyback converter can be applied has been considered to be 200 W due to the limitation of cost. However, the present invention greatly reduces the ripple component contained in the input current. The burden on both electrolytic capacitors on the secondary side is reduced, and it can be applied to a power supply of 200 W or more at the same cost as a half bridge or a full bridge. When the voltage on the secondary side exceeds 24 V, the flyback method may be preferred rather than the limitation of the withstand voltage of the diode on the secondary side. Can be expected as an alternative to.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the invention described in claim 2;

FIG. 3 is a waveform diagram of FIG.

FIG. 4 is a waveform diagram of FIG.

FIG. 5 is a circuit diagram showing one example of a conventional system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2nd transformer 1a Primary winding 1b Secondary winding 2 2nd switch element 3 Impedance element 4 3rd switch element 5 Capacitor 6 Resistance 7 2nd diode 8 AC power supply 9 Center tap diode 10 Full wave rectifier DESCRIPTION OF SYMBOLS 11 1st smoothing capacitor 12 1st transformer 12a Primary winding 12b Secondary winding 12c Tertiary winding 12d Secondary winding 13 First switch element 13a Switch element 13b Switch element 14 Oscillation control circuit 15 First 16 Diode 16 Second smoothing capacitor 17 Load 18 Reactor 19 Diode 20a Capacitor 20b Capacitor 21 DC power supply

[Procedure amendment]

[Submission date] April 2, 2001 (2001.4.2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the invention described in claim 2;

FIG. 3 is a waveform diagram of FIG.

FIG. 4 is a waveform diagram of FIG.

FIG. 5 is a circuit diagram showing one example of a conventional system.

6 is a waveform diagram of FIG.

[Description of Signs] 1 Second transformer 1a Primary winding 1b Secondary winding 2 Second switch element 3 Impedance element 4 Third switch element 5 Capacitor 6 Resistance 7 Second diode 8 AC power supply 9 Center tap Diode 10 Full-wave rectifier 11 First smoothing capacitor 12 First transformer 12a Primary winding 12b Secondary winding 12c Tertiary winding 12d Secondary winding 13 First switch element 13a Switch element 13b Switch element 14 Oscillation Control circuit 15 First diode 16 Second smoothing capacitor 17 Load 18 Reactor 19 Diode 20a Capacitor 20b Capacitor 21 DC power supply

Claims (2)

[Claims] 1. An AC power supply, a full-wave rectifier, a first smoothing capacitor, a first transformer having a primary winding and a secondary winding, and a series connected to a primary winding of the first transformer. A first switch element connected to the first transformer, a first diode connected in series to a secondary winding of the first transformer,
A second smoothing capacitor for charging a component of an AC voltage generated in a secondary winding of the transformer passing through the first diode, a load for supplying a voltage of the second smoothing capacitor, and a second smoothing capacitor In a flyback converter provided with an oscillation control circuit for controlling the oscillation of the first switch element in order to keep the voltage of the first switch element constant, a second transformer having a primary winding and a secondary winding is connected to the primary transformer. One end of the winding is connected to one terminal of the first smoothing capacitor, and the other end is connected to the other terminal of the first smoothing capacitor via a second switch element. One end of the wire is connected to one terminal of the second smoothing capacitor via a second diode, and the other end is connected to the other terminal of the second smoothing capacitor. Winding winding The terminal through an impedance element connected to the control electrode of said second switching element,
A third switch element is connected to the control electrode of the second switch element, a capacitor is connected to the control electrode of the third switch element, and one terminal of the tertiary winding is connected to the third electrode.
A switching power supply device, wherein a resistor is connected between control electrodes of the switch element. 2. The switching power supply according to claim 1, wherein one end of a primary winding of the second transformer is connected to each terminal of the AC power supply via a center tap diode.