Fault detection method of switching power supply
After having a basic understanding of switching power supply, let's look at the fault detection and maintenance methods.
First, observe whether the power fuse is damaged. If the fuse tube is damaged, it can't be replaced in a hurry. You must first check whether there is a short circuit in the power supply. Methods: Test the AC end behind the fuse of the power supply (test point 1) with the electric block of a multimeter, and its normal resistance should be above tens of thousands of ohms. If the resistance is zero, it indicates that there is AC short circuit in the power supply. In addition, we should also focus on checking whether the AC filter capacitor of the power supply is damaged; At the same time, if there is a varistor, you should also check this resistor.
If the above test results are normal, we should then test the four rectifier diodes of the power supply (test point 2). Under normal conditions, the forward resistance of the diode is several k (measured by multimeter× 1k), and the reverse resistance is close to infinity. If it is found that the test result is abnormal, it needs to be replaced. Following the investigation, the next thing to do is to test the DC resistance of the power supply (test point 3), and its normal resistance is also several K. If the resistance is zero, it means that there is a DC short circuit. There are many reasons for DC short circuit, such as the short circuit damage of filter capacitor, the damage of power supply oscillation tube, the damage of oscillation integrated block and peripheral circuit, which may all cause short circuit. Here, it should be noted that before replacing the power supply oscillating tube, it is necessary to ensure that the oscillating integrated block and peripheral circuits are normal, otherwise the power supply tube will be damaged again.
After eliminating the above problems of switching power supply, it shows that most faults exist in oscillation control circuit, sampling feedback circuit or load. At this time, we should first check whether the power supply circuit of the oscillating integrated block is normal (test point 4), and its normal voltage should be about 10V (special reminder: since the test voltage should be conducted under the condition of electrification and there is high-voltage commercial power on the power board, we should pay special attention to personal safety, and do not try to directly touch any part of the power supply).
If there is no voltage at this point or the voltage is very low, first check whether the step-down resistor is damaged; Secondly, check whether the oscillation integrated block and its external power supply circuit are normal. If no fault is found in the peripheral circuit, it is recommended to replace the oscillation integrated block. Of course, sometimes the power supply can't output voltage normally, which may also be caused by the short circuit of the load to protect the power supply. For this power supply, we only need to unplug the output line and check whether the output voltage is normal (test point 5), and then we can determine the fault position. After the previous troubleshooting, we should finally check the feedback circuit. Generally speaking, this part of the fault mainly focuses on the photoelectric coupler and its amplification circuit, so we should pay special attention to it.
summary
Of course, the above method can't solve all the problems of power supply, but it is effective for some problems that are easy to occur in daily switching power supply. I hope that this introduction can play a role in attracting jade and help everyone solve the small problems encountered in switching power supply.
