First begin to describe the switching power supply design and production process of it, let us talk about PCB design. Switching power supply operating at high frequency, high pulse state, analog circuits are a special kind of. The principles to be followed by a high-frequency circuit wiring layout when.
1. Layout: pulse voltage wiring as short as possible, where the input switch to the transformer connection, output transformer rectifier connected to the line. Pulse current loop as small as the input filter capacitor being returned to the transformer to switch capacitor negative. Transformer rectifier output section to the end to find the output capacitor return output transformer circuit X capacitor as close to the input of the switching power supply, input lines should be avoided with other circuits in parallel, should be avoided. Y capacitor should be placed in the cabinet or ground terminal FG connector. Total touch induction and transformer to maintain a certain distance in order to avoid magnetic coupling. Such as poor treatment can add a touch shield in total inductance of the transformer room, more than a few of the EMC performance switching power supply greater impact.
The output capacitor generally adopt a near two rectifier output should be close to the other terminal, can affect the power output ripple indicators, two small-capacity capacitor in parallel with the effect should be better than using a large-capacity capacitor. Heating devices and electrolytic capacitors must maintain a certain distance in order to prolong the life of the machine, is a switching power supply electrolytic capacitors fresh bottle life, such as transformers, power management, power resistors and electrolytic must keep a distance, it must be set aside space for heat dissipation between electrolysis , conditions permitting, it can be placed in the inlet.
The control section to note: the high-impedance weak signal circuit wiring should be as short as sampling of the feedback loop, in dealing with to try to avoid interference, current sampling signal circuits, especially current control circuit, easy to deal with some unexpected bad the accident, which has some skill, is to 3843 circuit example shown in Figure (1) Figure I better than Figure II, Figure II when loaded with the current waveform on the oscilloscope observation obviously superimposed spikes, current limit due to interference than the design value low a figure no such phenomenon, as well as the drive signal switch circuit, the switch drive resistor to be close to the switch, the switch can improve reliability, this DC resistance and high voltage power MOSFET driver characteristics.