Power adapter for overheating protection circuit!

The heat source of power adapter is mainly Schottky rectifier diode, high frequency switching transformer, power MOS tube, filter electrolytic capacitor, among which the power MOS tube, high frequency transformer and rectifier Schottky diode temperature rise is more prominent. In order to prevent the power adapter from overheating and damage, the design of switching power adapter not only requires the use of electronic components with good high temperature characteristics, but also requires the printed PCB board, heat sink, high frequency transformer and other reasonable design, advanced production technology, and the need to take overheating protection measures, these are in order to ensure safety must have the conditions.

In order to restrain the temperature rise of the power adapter, in addition to choosing the power MOS tube with small leakage current and short storage time, it is also necessary to install a heat sink for the power MOS tube. It has been proved that the stability of the power adapter will be greatly improved and the loss rate will be significantly reduced after the MOS tube is installed with heat sink. The function of the electronic switch overheating protection is to cut off the AC input line of the power adapter or force off the modulated pulse output to stop the high-frequency oscillation before the temperature of the hot-prone component or power housing in the power adapter exceeds the specified limit.

The types of overheating protection for power adapters can be classified as automatic reset, manual reset, non-renewable, non-reset, and various other types that provide equivalent overheating protection.

Overheating protector and switching power supply constitute a whole, need to pay attention to the location, distance to accept heat source, replaceable difficulty, etc. The most basic placement requirements are not subject to mechanical collision, easy to disassemble and assemble; When the function of the protector is related to polarity, it is connected with a flexible wire. The device with no polarity plug should have a overheating protector on the two leads; When the circuit of the protector is disconnected, it does not affect the normal operation of the power adapter, nor can it cause fire or damage the electrical equipment. Usually, the circuit board area of the power adapter and the space in the plastic shell are relatively small, so it is difficult to use the overheating protector. If the heat protector is difficult to fit in, a temperature fuse or thermistor can be used as the heat protector. Stick it on the surface of the heat sink of the high-frequency transformer or power MOS tube. When the temperature rises to a certain value, the overheating protection switch can automatically cut off the power supply, or force the output of the modulation pulse to stop the high-frequency oscillation.

If the power adapter uses a control driver IC with overheating protection function, then do not need to add any peripheral components or only need to add very few peripheral components, can play the role of overheating protection. Because the power adapter uses the control drive integrated circuit has built in the PN junction temperature sensor, containing overheating off circuit. The driver IC without built-in PN junction temperature sensor needs to be connected with a temperature sensing element outside it. The use of drive integrated circuit with overheat shutdown circuit, so that overheating protection becomes very simple, and the price of integrated circuit itself is very low, its performance price ratio is very high.