Wiring principles for switching power supplies in high frequency circuits
Layout: The pulse voltage lines are as short as possible, including the input switching tube to the transformer line and the output transformer to the rectifier connection line. Pulse current loop as small as possible, such as the input filter capacitor positive to the transformer to the switching tube return capacitance negative. Output part of the transformer output to the rectifier to the output current to the output capacitor return transformer circuit X capacitor should be as close as possible to the input of the switching power supply, the input line should be avoided and other circuits parallel, should be avoided. Y capacitor should be placed in the chassis ground terminal or FG connection. Keep a certain distance between the common touch inductor and the transformer to avoid magnetic coupling. If it is not good to deal with the common touch inductance and transformer to add a shield between the above items have a greater impact on the EMC performance of the switching power supply.
Output capacitance can generally use two a rectifier near the other should be close to the output terminals, can affect the power supply output ripple indicators, two small capacity capacitors in parallel should be better than a large-capacity capacitor. Heat-generating devices and electrolytic capacitors to maintain a certain distance to extend the life of the machine, electrolytic capacitors is a switching power supply life of the bottle, such as transformers, power tubes, high-power resistors and electrolytic distance, electrolytic space between the heat dissipation must also be left, conditions permit can be placed in the air intake.
Control section should pay attention to: high impedance weak signal circuit connection to be as short as possible, such as sampling feedback loop, when dealing with to try to avoid interference, current sampling signal circuits, especially current-controlled circuits, poorly handled prone to some unexpected accidents, as well as the switching tube drive signal circuits, the switching tube drive resistor to be close to the switching tube to improve the switching tube reliability, which is related to the high DC impedance voltage driving characteristics of the power MOSFETs. DC impedance voltage drive characteristics.
