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Single chip switching power supply design

2015-03-21 14:42  
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Single chip switching power supply design
The typical application circuit of TOPSwitch series single chip switching power supply is shown in the diagram. High-frequency transformer in the circuit has three functions of energy storage, isolation output and voltage transformation. The diagram shows thatthe polarity of high frequency transformer primary winding Np is coincided with the opposite polarity of secondary winding Ns and the feedback winding NF. This indicates that the electrical energy is stored in the primary winding in the type of magnetic energy when TOPSwitch is broken over, and meanwhile VD2 is closed. When TOPSwitch is cut off, VD2 is broken over, energy will transfers to the secondary, namely, it is the features of fly-back switching power supply. In the diagram, BR is the rectifier bridge; Cin is the input end offilter capacitor. AC voltage u is rectified and filtered and then it will get DC high voltage V1. After passing the primary windings, it will add to the drain of TOPSwitch. In view of the TOPSwitch cut-off time, the spike voltage generated by drain of high frequency transformer can be superimposed on the DC high voltage V1 and the induced voltage Vor. It can make the brain voltage of power switching tube exceed 700V and damage the chip. So it must increase drain clamping protection circuit in the justified of primary winding.

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