GRAPHITE SHEET USED IN SWITCHING POWER SUPPLY

There are a lot of high-power semiconductor devices such as rectifier bridge stack, high current rectifier tube, high-power triode or field effect transistor. If the heat of these parts with large heat output cannot be reasonably discharged, the normal operation of switching power supply will be affected. In order to improve the stability of switching power supply, in the thermal design of switching power supply, then heat dissipation has become a very important part in the design of switching power supply. Several methods commonly used in the thermal design of switching power supply are: using passive heat dissipation (radiator, cooling fan), metal PCB, graphite sheet (in practical application, the above methods should be applied to the switching power supply with the best and most reasonable scheme according to the requirements of customers). The following describes the application of thermal conductive graphite sheet in switching power supply to solve the heating problem:

1. From the point of view of heat dissipation, it is better to install the printed board vertically, and the distance between boards should not be less than 20 mm. 

2. The devices on the same printed circuit board shall be arranged according to their calorific value and degree of heat dissipation as far as possible. The devices with small calorific value or poor heat resistance (such as small signal transistors, small scale integrated circuits, electrolytic capacitors, etc.) shall be placed at the top stream (entrance) of the cooling air flow; devices with high heat output or good heat resistance (such as power transistors, large scale integrated circuits, etc.) are placed at the downstream of the cooling air flow.

3. In the horizontal direction, the high-power devices should be arranged close to the edge of the printed circuit board as far as possible to shorten the heat transfer path; in the vertical direction, the high-power devices should be arranged close to the top of the printed circuit board as far as possible, so as to reduce the influence of these devices on the temperature of other devices. 

4. The temperature sensitive devices should be placed in the lowest temperature area (such as the bottom of the equipment), and it should not be placed directly above the heating device. Multiple devices should be staggered on the horizontal plane. 

5. The heat dissipation of printed circuit board in the equipment mainly depends on air flow, so the air flow path should be studied in the design, and the device or printed circuit board should be reasonably configured. When air flows, it always tends to flow at the place with small resistance, so when configuring devices on the printed circuit board, it is necessary to avoid leaving a large space in a certain area. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.