What is the high voltage of the switching power supply?
The switching power supply has a high pulse state and belongs to a special type in the analog circuit. The high frequency circuit wiring principle must be followed when laying the board.
1. Layout: The pulse voltage connection is as short as possible. The input switch is connected to the transformer and the output transformer is connected to the rectifier. The pulse current loop is as small as possible as the input filter capacitor is positive to the return capacitance of the transformer to the switch. Output part of the transformer output to the rectifier to the output inductor to the output capacitor return transformer circuit X capacitor should be as close as possible to the input end of the switching power supply, the input line should avoid parallel with other circuits, should be avoided. The Y capacitor should be placed at the chassis ground terminal or FG connector. The total inductance is kept at a certain distance from the transformer to avoid magnetic coupling. If it is not handled well, a shield can be added between the common inductor and the transformer. The above items have a great influence on the EMC performance of the switching power supply.
The output capacitor can generally be used with two ones close to the rectifier and the other should be close to the output terminal, which can affect the output ripple index of the power supply. The parallel effect of two small-capacity capacitors should be better than using a large-capacity capacitor. The heating device should be kept at a certain distance from the electrolytic capacitor to extend the life of the whole machine. The electrolytic capacitor is the bottle strength of the switching power supply life. For example, the transformer, the power tube, the high-power resistor must be kept away from the electrolysis, and the heat dissipation space must be left between the electrolysis. , conditions allow it to be placed at the air inlet.
The control part should pay attention to: the high-impedance weak signal circuit should be as short as possible as the sampling feedback loop. When processing, try to avoid the interference, current sampling signal circuit, especially the current control type circuit. The accident, there are some tricks, the effect of the 3843 circuit is better than the obvious superimposed spike on the current waveform when the oscilloscope is fully loaded. Since the interference current limit is lower than the design value, there is no such phenomenon in Figure 1. There is also a switching tube driving signal circuit, and the switching tube driving resistor is close to the switching tube, which can improve the working reliability of the switching tube, which is related to the high DC impedance voltage driving characteristic of the power MOSFET.
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