Switching power supply maintenance skills
1. For the failure of the fuse burning or exploding, mainly check the large filter capacitor on the 300V, the diodes of the rectifier bridge and the switch tube and other parts. The problem of the anti-interference circuit will also cause the fuse to burn and turn black.
Note: The fuse burning due to the breakdown of the switch tube will generally burn out the current detection resistor and the power control chip. Negative temperature coefficient thermistors are also easy to burn out along with fuses.
2. For no output, the phenomenon that the fuse is normal indicates that the switching power supply is not working or has entered a protection state. Electrician world
First, measure whether the start-up pin of the power control chip has a start-up voltage. If there is no start-up voltage or the start-up voltage is too low, check whether the start-up resistor and the components connected to the start-up pin are leaking current. If the power control chip is normal, the above inspection Faults can be found quickly.
If there is a start-up voltage, measure whether the output terminal of the control chip has jumps of high and low levels at the moment of power-on. If there is no jump, it means that the control chip is damaged, the peripheral oscillation circuit components or the protection circuit have problems, and the control can be replaced first. Chip, and then check the peripheral components; if there is a jump, it is generally a bad or damaged switch.
3. For the fault with output voltage, but the output voltage is too high, it generally comes from the voltage stabilization sampling and voltage stabilization control circuit. (www.dgjs123.com) The DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits together form a closed control loop, any problem will cause the output voltage to rise.
4. The load of the switching power supply has a short-circuit fault (especially the DC/DC converter is short-circuited or has poor performance, etc.). At this time, all loads of the switching power supply circuit should be disconnected to distinguish whether the switching power supply circuit or the load circuit is faulty.
If the voltage output of the disconnected load circuit is normal, it means that the load is too heavy; or if it is still abnormal, it means that the switching power supply circuit is faulty.
5. For the failure of the rectifier diode and filter capacitor at the output voltage end, it can be judged by the substitution method.
In short, the maintenance of switching power supply faults is easy or difficult, but as long as you grasp its core things, that is, fully familiar with the basic structure and characteristics of switching power supply, it can quickly eliminate switching power supply faults and achieve multiplier effect.
