A Soft-Off Power Converter

Abstract

The invention provides a soft-off power converter, which includes a transformer connected between the input power supply and the output power supply. The primary winding of the transformer is connected in series with the negative terminal of the input power supply and a circuit control switch is controlled by the output signal of the PWM control circuit. To control on-off, a branch circuit in which the second capacitor, the rectifier diode and the first capacitor are connected in series is connected between the primary winding of the transformer and the negative terminal of the input power supply, and the voltage control switch is controlled by a soft-off control circuit. The invention solves the problem of It solves the problem of large loss caused by hard turn-off of the switch, realizes soft turn-off, reduces switching loss, improves efficiency, and also solves the problem of power supply when the control circuit is working and the problem of absorbing the turn-off peak voltage of the switch. The power converter does not need to be provided with a power supply circuit and a absorption circuit, and the circuit structure is simplified.

Description

technical field [0001] The invention relates to the technical field of control of electronic circuits, in particular to a power converter for controlling a power switch to realize soft shutdown. Background technique [0002] At present, in the single-ended power converter, due to the leakage inductance of the transformer, a high reverse voltage peak will be generated at both ends of the switch tube when the switch tube in the power converter is turned off, which may exceed the withstand voltage of the switch tube and cause The switch tube is damaged, and in order to improve the conversion efficiency of the single-ended power converter, the switch tube must be soft-switched to reduce the switching loss. [0003] The known quasi-resonant QR mode single-ended power converter can only achieve zero-voltage turn-on, the switch tube is still hard off, the turn-off loss is relatively large, the conversion efficiency of the power converter is low, and the leakage inductance of the tr...

AI Technical Summary

Problems solved by technology

[0003] The known quasi-resonant QR mode single-ended power converter can only achieve zero-voltage turn-on, the switch tube is still hard off, the turn-off loss is relatively large, the conversion efficiency of the power converter is low, and the leakage inductance of the transformer still needs to be used for energy storage Commonly used as attached Figure 4 The structure diagram of an RCD absorption circuit with absorption function is shown to absorb, the energy stored in the leakage inductance is dumped into the capacitor C and part of it is consumed by the resistance R, and the electric energy is wasted without benefit

[0004] The existing circuits for reducing the turn-off loss of the switching tube mainly include active clamping circuits and auxiliary image 3 An RCD snubber circuit with absorption and soft turn-off functions is shown, the active clamping technology can greatly reduce the turn-off voltage peak of the switch tube, so that the product of voltage and current when the switch tube is turned off is reduced, so that the turn-off The turn-off loss is reduced, but the soft turn-off effect of the switch tube is not obvious, and the turn-off loss of the switch tube cannot be further reduced; image 3 In the RCD snubber circuit shown, during the off-time of the switch tube, the power supply voltage and the leakage inductance peak voltage are superimposed to charge the capacitor C through the diode D and the primary winding of the transformer, and the voltage across the capacitor C rises slowly. At this time, the switch tube During the turn-off process, the current drops sharply, so that the overlapping area of ​​voltage and current is very small, that is, the power loss is small, and the switch tube is softly turned off. During the conduction period of the switch tube, the energy stored in the capacitor C passes through the resistor R And the switch tube discharges, and the electric energy consumes part of the resistance R, so that the terminal voltage of the capacitor C drops, and prepares for the capacitor C to absorb the leakage inductance energy storage in the next cycle. In this mode, the electric energy is still wasted without benefit. Even the electric energy consumed by the resistor is much more than the electric energy saved by the soft turn-off of the switch tube, which makes this circuit lose its use value in today's energy-saving promotion

[0005] Moreover, the control circuit in the current power converter needs an external power supply to work. Generally, another independent small power supply or standby power supply is used for power supply, or a power supply winding is set in the transformer to provide auxiliary power supply, which makes the power supply more complicated and wastes electronic materials. high cost

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