Power Supply Troubleshooting Methods - Power Supply Troubleshooting Ideas
Switching power supply is an indispensable part of various electronic equipment, and its performance is directly related to the technical indicators of electronic equipment and whether it can work safely and reliably. Because the key components inside the switching power supply work in the high-frequency switching state, the power consumption is small, the conversion rate is high, and the volume and weight are only 20%-30% of the linear power supply, so it has become the mainstream product of the regulated power supply. The maintenance of electrical faults of electronic equipment, in line with the principle of starting from easy to difficult, basically starts with the power supply first, and then repairs other parts after confirming that the power supply is normal, and power supply failures account for most of the electrical failures of electronic equipment . Therefore, understanding the basic working principle of the power supply at the beginning, and being familiar with its maintenance skills and common faults will help shorten the maintenance time of electronic equipment failures and improve personal equipment maintenance skills.
1. No output, fuse is normal
This phenomenon indicates that the switching power supply is not working or has entered a protection state. First of all, it is necessary to measure whether the starting pin of the power control chip has a starting voltage. If there is no starting voltage or the starting voltage is too low, check whether the starting resistor and the external components connected to the starting pin are leaking. If the power control chip is normal at this time, the above inspection Faults can be found quickly. If there is a starting voltage, measure whether the output terminal of the control chip has high or low level jumps at the moment of starting up. If there is no jump, it means that the control chip is broken, there is a problem with the peripheral oscillation circuit components or the protection circuit, 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 tube.
2. Insurance burning or frying
Mainly check the large filter capacitor on the 300V, the diodes of the rectifier bridge, and the switch tubes. Problems with the anti-interference circuit will also cause fuses to burn and blacken. It should be noted that the fuse burnout caused by the breakdown of the switch tube will generally burn out the current detection resistor and the power control chip. NTC thermistors are also easily burned out together with the fuse.
3. There is output voltage, but the output voltage is too high
This kind of failure generally comes from the voltage regulation sampling and voltage regulation control circuit. 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 output voltage is too low In addition to the voltage regulation control circuit will cause the output voltage to be low, there are also the following reasons that can also cause the output voltage to be low:
a. The switching power supply load has a short circuit fault (especially the DC/DC converter short circuit or 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.
b. The failure of the rectifier diode and filter capacitor at the output voltage end can be judged by the substitution method.
c. The performance degradation of the switch tube will inevitably lead to the failure of the switch tube to conduct normally, which will increase the internal resistance of the power supply and reduce the load capacity.
