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The heat sources of linear power adapter are mainly Schottky rectifier diode, high frequency switching transformer, power MOS transistor and filtered electrolytic capacitor. The temperature rise of power MOS transistor, high frequency transformer and rectified Schottky diode is more prominent. In order to prevent the linear power adapter from being damaged due to overheating, the switch design requires not only the use of electronic components with good high temperature characteristics, but also the reasonable design and advanced production process of printed circuit board, heat sink and high-frequency transformer, as well as the need to take overheating protection measures, which are necessary to ensure safety.
In order to suppress the temperature rise of linear power supply adapter, in addition to selecting power MOS transistor with small leakage current and short storage time, it is also necessary to add heat sink to power MOS tube. It has been proved that the stability of the linear power adapter will be greatly improved and the loss rate will be significantly reduced after the MOS tube is equipped with heat sink. The function of electronic switch overheating protection measures is to cut off the AC input line of linear power adapter, or force the modulation pulse output to stop high-frequency oscillation before the temperature of components or power supply shell in linear power adapter exceeds the specified limit value.
The overheat protection types of linear power adapter can be divided into the following categories:
Automatic reset type, manual reset type, non renewable, non reset type and other types that can provide equivalent overheating protection.
It is necessary to pay attention to the placement position, the distance of receiving heat source and the difficulty of replacement when the overheat protector and switching power supply are integrated. If the linear power adapter adopts control drive IC with overheat protection function, it can play the role of overheat protection without adding any peripheral components or only a very small number of peripheral components. Because the control drive IC of linear power adapter has built-in PN junction temperature sensor and overheat shutdown circuit. The driving IC without built-in PN junction temperature sensor needs to be connected with a temperature sensing element outside it.