JPH0630559A - Resonance type switching power source - Google Patents

Abstract

PURPOSE:To reduce the noise current even if secondary winding are coupled densely by connecting an insulated transformer, whose primary winding is divided into two, a reactor for resonance, and a capacitor for resonance between the junctions between the switch elements of two sets of arms where two switch elements are connected each in series. CONSTITUTION:The primary side of an insulated transformer 20 is connected, being divided into the primary windings 21 and 22 the same in the numbers of windings, between the two junctions which connect two switch elements 2 and 3, and 4 and 5. One end each of the primary windings 21 and 22 are connected to the junctions between switch elements, and a resonance reactor 6 and a resonance capacitor 7 are connected in series between the primary windings 21 and 22 so as to form a full bridge series resonance circuit. The secondary winding 23 of the insulated transformer 20 is wound so that it may be the same coupling as the primary windings 21 and 22. Diodes 8 are connected to both ends of the secondary winding 23, whereby both waves are rectified, and they are converted into DC voltage little in ripple by a smoothing capacitor 9. Hereby, even if the secondary windings are coupled densely, the input feedback noise that the switch circuit generates is offset, and the conversion efficiency of a transformer is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type switching power supply, and more particularly to reducing noise generated from the switching power supply.

[0002]

2. Description of the Related Art In recent years, a resonance capacitor and a resonance reactor are connected in series to form a series resonance circuit,
A so-called resonance type switching power supply has been put into practical use, which performs power conversion with low noise and high efficiency by utilizing the resonance current flowing in the resonance circuit. In this switching power supply, an insulating transformer is often used for the purpose of performing insulation between input and output and voltage conversion.

In such a switching power supply,
Since the leakage inductance of the transformer converted to the primary side of the transformer acts as a part of the resonance reactor, in order to avoid heat generation of the transformer due to the leakage inductance and improve the efficiency of the transformer, the primary and secondary windings are As a tight coupling, it is necessary to minimize the leakage inductance.

A conventional example of a switching power supply using a series resonance circuit will be described with reference to FIG. In the figure, 1 is a DC power supply obtained by rectifying and smoothing a commercial AC power supply, or a voltage source such as a storage battery, and 2 to 5 are switch elements equipped with flywheel diodes capable of passing current in the reverse direction. A resonance reactor 6, a resonance capacitor 7 and a transformer 20 are connected in series at a connection point between the switch elements 2 and 3 and a connection point between the switch elements 4 and 5.

The switch elements 2 and 5 and the switch elements 3 and 4 are alternately turned on at the same time, and an input power supply voltage is alternately inverted and applied to a series resonance circuit composed of a transformer, a resonance reactor and a resonance capacitor. A high frequency of several tens of kHz is generally used as this frequency in order to miniaturize the transformer and the resonance reactor.

The high frequency voltage generated in the secondary winding 23 of the transformer is rectified by the rectifying diode 8 and converted into a DC voltage with less ripple by the smoothing capacitor 9.

Considering the case where the switch elements 2 and 5 are conducted, the equivalent circuit is as shown in FIG. At this time, the primary winding of the transformer is connected to the negative side of the input power source.
Next, considering the case where the switch elements 3 and 4 are conducted, the equivalent circuit is as shown in FIG.
The secondary winding is connected to the positive side of the input power supply.

As described above, with the switching operation, the primary windings of the transformer are alternately connected to the positive side and the negative side of the input power source. At this time, the potential of the secondary winding, which is electrostatically coupled to the primary winding by the stray capacitance 26 between the primary and secondary windings of the transformer, reciprocates between the positive side and the negative side of the input power supply along with the switching operation. As a result, the stray capacitance between the primary and secondary windings is charged and discharged, and a common mode (in-phase) noise current flows between the primary circuit and the secondary circuit of the transformer. For the above reasons, there is a problem that the input feedback noise of the switching power supply increases if a transformer with good coupling between windings is used for the purpose of lowering the temperature of the transformer.

In addition, as shown in FIG. 5, a common mode choke coil 30 is often inserted in the circuit to suppress the common mode noise current.
However, in this method, since the iron core is mounted in the main circuit, there are problems that the wiring length becomes long, the loss increases, and the cost rises.

Therefore, the object of the present invention is to make the primary of the transformer 2
It is to provide a switching power supply with low input feedback noise by reducing the common-mode noise current while improving the efficiency of the transformer by tightly coupling the secondary windings.

[0011]

In order to achieve the above object, the present invention has two sets of arms in which two switch elements are connected in series, and a resonance reactor is provided between connection points of the switch elements of each arm. In a full-bridge series resonance type switching power supply in which the primary windings of a resonance capacitor and an insulating transformer are connected in series, the primary winding of the insulating transformer is divided into two in series, and one end of the first winding is The second winding is connected to the connection point of the switch element of the first arm, one end of the second winding is connected to the connection point of the switch element of the second arm, and the other end of the first winding and the second winding are connected. The resonance reactor and the resonance capacitor are connected in series between the other ends of the.

[0012]

In the present invention, the primary winding of the transformer is divided into two, and the resonant capacitor and the resonant reactor are inserted between them, so that even if a tightly coupled transformer is used, the secondary winding of the transformer accompanying the switching operation is The potential change amount is small, and the in-phase noise current flowing between the primary and secondary windings can be reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a switching power supply according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram for explaining the present invention. A transformer primary winding half 21, a resonant reactor 6, a resonant capacitor 7, and a primary winding remaining half 22 are connected in series between the connection points of the switch elements 2 and 3 and the switch elements 4 and 5. ing. The winding 21 and the winding 22 have the same number of turns, and are designed so that the coupling with the secondary winding is equal to each other.

Considering the case where the switch elements 2 and 5 are conducted, the equivalent circuit is as shown in FIG. At this time, the primary winding 21 of the transformer is connected to the positive side of the input power source.
Is connected to the negative side. Next, considering the case where the switch elements 3 and 4 are conducted, the equivalent circuit is as shown in FIG.
At this time, the primary winding 22 of the transformer is on the positive side of the input power source,
The same 21 is connected to the negative side.

Next, consider the stray capacitance between the primary and secondary windings. The stray capacitance 24 between the primary winding 21 and the secondary winding 23 is C
If the stray capacitance 25 between the other 22 of the primary windings and the secondary winding 23 is C2, the stray capacitance is equal because of the equal coupling between the windings, and C1 = C2.

If C1 = C2, then FIG.
In each switching state of (B), the secondary winding 23
Does not change with respect to the input power source. As a result, it is possible to prevent a common mode (in-phase) noise current from flowing between the primary circuit and the secondary circuit of the transformer.

[0017]

As described above, according to the present invention, the heat generation of the transformer can be avoided by changing the connection method of the primary winding of the transformer, and at the same time, the input feedback noise generated from the switching power supply can be avoided. Can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a resonance type switching power supply showing an embodiment of the present invention.

2A is an equivalent circuit diagram in a state where the switch elements 2 and 5 are in conduction in FIG. 1, and FIG. 2B is an equivalent circuit diagram in a state in which the switch elements 3 and 4 are in conduction in FIG.

FIG. 3 is a circuit diagram of a conventional resonant switching power supply.

4A is an equivalent circuit diagram in a state where the switch elements 2 and 5 are conducting in FIG. 3, and FIG. 4B is an equivalent circuit diagram in a state where the switch elements 3 and 4 are conducting in FIG.

FIG. 5 is a diagram showing a conventional common mode noise current suppression example.

[Explanation of symbols]

 1 Input power supply 2 to 5 Switch element 6 Resonance reactor 7 Resonance capacitor 8 Rectifying diode 9 Smoothing capacitor 20 Transformer 21 First winding 22 Second winding 23 Secondary winding

Claims (1)

[Claims] 1. A pair of arms, each having two switch elements connected in series, is provided, and a resonance reactor, a resonance capacitor, and a primary winding of an insulating transformer are connected in series between connection points of the switch elements of each arm. In the connected full-bridge series resonance type switching power supply, the primary winding of the insulating transformer is divided into two in series, and one end of the first winding is connected to the connection point of the switch element of the first arm. One end of the second winding is connected to the connection point of the switch element of the second arm, and the resonance reactor and the resonance capacitor are connected in series between the other end of the first winding and the other end of the second winding. A resonant switching power supply characterized by being connected.