Step 1: Immediately Cut Power and Check External Factors
When the switching power supply triggers over-voltage protection (OVP), first disconnect the input power. Check whether the input voltage exceeds the rated range of the power supply and whether there is a sudden change or open circuit in the load. After ruling out external factors, proceed to diagnose the power supply itself.
Step 2: Focus on Inspecting the Feedback Loop and Regulation Circuit
The most common cause of over-voltage protection is a failure in the feedback loop. Focus on checking the TL431, optocoupler, and surrounding resistors for cold solder joints, open circuits, or degradation. If the voltage divider ratio of the sampling resistors is incorrect, it will cause the output voltage to spike and trigger protection. Also, check the output filter capacitors for bulging or leakage.
Step 3: Test Key Components and Replace
After powering off, discharge the output filter capacitors. Use a multimeter to measure the Zener diode, the VCC of the PWM control chip, and the reference pin voltage. Once the faulty component is identified, replace the feedback resistor, optocoupler, or control chip with one of the same specification. Before powering on again, it is recommended to connect a dummy load, gradually adjust and test the voltage, and confirm that the output voltage is stable within the normal range before putting it into formal use.