JPS5836232Y2 - Surge absorption circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a surge absorption circuit used in a switching regulator having a transformer.

In a switching regulator having a transformer, a surge voltage is generated during switching due to the leakage inductance of the transformer.

This surge voltage has the potential to destroy switching elements such as transistors, so some kind of surge absorption circuit must be provided, but conventionally surge absorption circuits consisting of a series or parallel circuit of a resistor and a capacitor have often been used. In addition to absorbing surge energy with a capacitor, the absorbed surge energy was consumed by a resistor.

However, in such a surge absorption circuit, the power consumed by the resistor becomes a loss, so as the switching power increases, this loss also increases, which is a major problem in improving the efficiency of the switching regulator. It becomes.

The present invention aims to eliminate the drawbacks of conventional devices as described above, and to realize a surge absorption circuit with a simple configuration that can improve efficiency as a switching regulator without wasting surge energy. This is the purpose.

The surge absorption circuit of the present invention does not consume the absorbed surge energy through resistance as in conventional devices.
This is supplied as an operating voltage to a circuit that requires a voltage higher than the input voltage, such as an inrush current control circuit, to improve the efficiency of the switching regulator.

The figure is a configuration diagram showing an embodiment of the surge absorption circuit of the present invention.

In the figure, R1 and R2 are resistors, C1 and C2 are capacitors, Tr1 to Tr3 are transistors, Dl and D2 are diodes, and T is a transformer.

A transformer T having a center tap on the primary winding, a capacitor C1 connected to the center tap, and switching transistors Tr2 and Tr3 connected to both ends of the primary winding are a DC/AC converter of a switching regulator. The switching transistors Tr2. T
By alternately turning r3 on and off, an alternating current voltage corresponding to the charging voltage of capacitor C1 is generated from the secondary winding of transformer T.

RCC is an inrush current control circuit made up of an inrush current limiting resistor R1 and a transistor Tr1, and limits the inrush current flowing into the capacitor C1 when the power is turned on.

One end of SVA is connected to the center tap of the primary winding of transformer T, and the other end is connected to diode D1. Switching transistor Tr2. A surge absorption circuit includes a capacitor C2 connected to the collector side of Tr3, and applies charging voltage Ec of the capacitor C2 to the base of the transistor Tr via a resistor R2.

The operation of the surge absorption circuit of the present invention configured as described above is as follows.

Switching transistor Tr2. When each Tr3 is turned off, the voltage applied to its collector is theoretically 2 Vcc, but as mentioned above, a surge voltage is generated due to the leakage inductance of the transformer T, so A voltage of 2VCC or more is applied.

However, this voltage is connected to the diode D1. D2
is absorbed by the capacitor C2 via the transistor Tr2. Extreme overvoltage is not applied to the collector of Tr3.

Here, since the charging voltage Ec of the capacitor C2 is discharged via the resistor R2, by appropriately selecting this discharge time constant, the charging voltage Ec is maintained at 2VCC, and the collectors of the transistors Tr2 and Tr3 are Can be clamped to Vcc.

In this way, since the capacitor C2 is always charged with a voltage of 2VCC, when viewed from the inrush current control circuit RCC side, a DC constant voltage source having a voltage of 2VCC is obtained.

For example, if the input voltage Vcc is directly used as the operating voltage of the inrush current control circuit RCC, the transistor Tr
The base potential of the transistor 1 reaches a maximum of Vcc, and the voltage drop at this portion is approximately several (V), resulting in a large loss.

On the other hand, if the voltage obtained from the surge absorption circuit SVA is used as the operating voltage of the inrush current control circuit RCC as in the present invention, the base potential of the transistor Tr1 can be maintained at a voltage higher than the input voltage Vcc.
The voltage drop in this portion can be significantly reduced, and the power loss in the rush current control circuit RCC can be reduced.

In the above explanation, the case where one end of the capacitor C2 of the surge absorption circuit SVA was connected to the center tap of the primary winding of the transistor T was exemplified, but this capacitor C
The same operation can be performed even if 2 is connected to the ground potential.

Furthermore, when using the charging voltage Ec of the capacitor C2 as an operating voltage for other circuits, if too much current is drawn, the voltage Ec will drop, but a constant DC voltage can still be obtained.

As explained above, the surge absorption circuit of the present invention supplies the absorbed surge energy to circuits that require a voltage higher than the input voltage. The loss of the circuit can be reduced, and the efficiency of the switching regulator can be improved.

[Brief explanation of the drawing]

The figure shows the configuration of an embodiment of the surge absorption circuit of the present invention. RCC...Inrush current control circuit, SVA...
...Surge absorption circuit.

Claims (1)

[Scope of utility model registration request] A switching regulator having a transformer and an inrush current control circuit connected to its input terminal, further comprising a capacitor connected to the primary winding of the transformer via a diode to absorb surge voltage generated in this winding. , a surge absorption circuit configured to supply the charging voltage of the capacitor to the inrush current control circuit as an operating voltage.