The 12 v switching power supply maintenance method

1, 12 v switching power supply insurance burn or Fried mainly check the 300 v on the filter capacitor, the diode rectifier bridge and switch tube parts, such as anti-interference circuit problems can also lead to insurance burning, black. It is important to note: because of the switch tube breakdown will cause burning generally the current sense resistor and power control chip burn out. Negative temperature coefficient thermistor is also easy to burn with insurance. 2, 12 v switching power supply output, insurance tube this phenomenon shows that switching power supply is not normal work or go into a state protection. First of all, to measure the power control chip start feet have start voltage, if not start voltage or start voltage is too low, should check the start resistance and start foot external components whether leakage, such as power supply control chip normal at this time, after the examination can find the fault quickly. If a start-up voltage, then measuring the output of the control chip in the boot instantly if there is a high and low level of the jump, if not jump, show control chip, peripheral oscillation circuit element, or bad protection circuit has a problem, can be substitution control chip, first check the peripheral components; If a jump, generally for switch tube bad or damaged. 3, 12 v switching power supply output voltage, but the fault generally comes from the high voltage output voltage sampling and voltage control circuit. In dc output resistance, sampling, sampling error amplifier such as TL431, optical coupling, the power control chip circuit constitute a closed control loop, any problems will result in higher output voltage. 4, 12 v switching power supply output voltage is too low, in addition to the voltage regulator control circuit can cause low output voltage, and here are some reasons can also cause low output voltage: a. Switching power supply load has a fault ( Short circuit or poor performance especially in DC/DC converter, etc. ) , at this point, all the load should disconnect switch power supply circuit, to distinguish is switch power supply circuit or load circuit fault. If disconnect the load circuit voltage output is normal, that is under the heavy load; Or is still not normal of switch power supply circuit fault. b。 Output voltage rectifier diode, filter capacitor failure, etc. , can be determine by the substitution method. c。 The switch tube performance degradation, inevitably lead to switch tube can't normal conduction, increase the resistance of power supply, load ability. d。 Switch transformer is bad, not only cause the loss of output voltage, also will cause the switch tube incentive not to damage the switch tube e repeatedly. Poor 300 v filter capacitance, the power load ability is poor, a load output voltage will drop.