Switch power supply and its lossless absorption circuit

Abstract

The non-loss absorber circuit comprises a first diode with cathode connected to input source positive end and anode connected to one end of inductance and capacitor, a second diode with anode connected to input source negative end, a capacitor with another end connected to switch element, an inductance with another end connected to cathode of second diode, and a clamping circuit with one end connected to source positive end and another end connected to second diode cathode to clamp the voltage of second diode on determined voltage when the switch element shuts. This invention decreases spike voltage and loss.

Description

【Technical field】 [0001] The invention relates to the field of switching power supplies. 【Background technique】 [0002] see figure 1 , which is a basic circuit of a single-ended flyback switching power supply. In this circuit, the input DC voltage is chopped into an alternating square wave voltage by controlling the on-off of the switch Q1, which is coupled to the secondary side through a transformer and then passed through The rectifier diode D rectifies to obtain the transformed voltage. However, this kind of circuit has the following disadvantages: due to the leakage inductance of the transformer and the stray inductance in the actual circuit, the switch Q1 will generate an induced voltage on the leakage inductance and stray inductance when it is cut off, so that the switch is easily damaged due to overvoltage . [0003] In order to reduce the voltage stress on the switch, an absorption or snubber circuit will be added to the switching device in the actual circuit, su...

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Problems solved by technology

However, this kind of circuit has the following disadvantages: due to the leakage inductance of the transformer and the stray inductance in the actual circuit, the switch Q1 will generate an induced voltage on the leakage inductance and stray inductance when it is cut off, so that the switch is easily damaged due to overvoltage

[0018] In this case, the loss of D2 is also greatly increased, which reduces the performance of the lossless absorption circuit. In order to solve this problem, it is necessary to choose a diode with high withstand voltage and fast switching speed, but according to the characteristics of the diode, the higher the withstand voltage of the diode, the The slower the switching speed, the two requirements are contradictory, limiting the range of applications for this circuit

In order to solve this contradiction, it is necessary to select a high-performance diode on the one hand, and on the other hand, it is necessary to control the minimum conduction time of the switch Q1 so that it is always greater than the resonance time Td of the L1, C1, and D2 circuits, that is But this will lead to a smaller adjustment range of the power supply. At the same time, the minimum duty cycle cannot be 0, and the power supply cannot be unloaded, which limits the application range.

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