source:Industry News Popular:adapter release time:2021-05-11 11:17:20 Article author:sznbone
Switching power supply with 12V use widely in life, such as monitoring camera, security protection, router, ADSL, interchanger, LCD monitor, LED lamp, portable DVD, speaker, etc. So, how to solve the problem when 12V switching power supply not work?
Fuse burning
Checking big filter capacitor, rectifier bridge and switching tube which above 300V, problem with anti-jamming circuit also causes fuse burning and become black. Attention that fuse burning causes by switching tube strike will burn current sense resistor and power supply controller.Negative termperature coefficient thermistor is easy to burn together with fuse.
SMPS no output, fuse ok
This describes SMPS doesn’t work or be protective. Firstly, test the starting point of the power controller and see if there is starting voltage. If no starting voltage or it is too low, then check the starting resistance and the component disjunctive to tarting point and see if there is electric leakage. If the power controller works noamal, it can find the problem asap after the above check. If there is starting voltage, checking the output of the controller and see if there is high or low change, if no, it obviously know that the controller broken, outer ascillating circuit or protective circuit with problem. Under this circumstance, change the controller, and check the outer components; if there is jump, it is normally switching tube broken.
There is output voltage but higher enough
This is from stabilibolt sampling and voltage stability control circuit. DC output, resistance sampling, error sampling amplifier such as TL431, optocoupler, switching controller and other circuits form a close contol loop, any problem will cause output voltage rise.
Output voltage lower enough
Except for the voltage stability control circuit which causes low voltage, below reasons also cause low voltage:
1. There is short trouble with the switching power supply(especially DC/DC converter short circuit or performance poor), at this moment, all loads should be switched off, so that to distinguish the problem with SMPS circuit or load circuit. If voltage output ok when switch off load circuit, it causes by overload; if not work, it is problem with SMPS circuit.
2. Switching transformer not work not only cause output voltage drop, but also cause switching tube damage.
3. Judge through method of substitution for the failure of output voltage of commutation diode and filter capacitor.
4. Performance reduction of switching tube must lead to the normal breakover of switching tube, enhance the internal resistance of SMPS, reduce the load capacity.
5. 300V filter capacitance failure leads to a poor load capacity, the output voltage will be reduced once loading.
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