1. What is the fault if the switching power supply voltage is normal but the current is very low?
The power supply output voltage is stable, but the current output is insufficient. This could be due to the following reasons:
1. Excessive internal resistance of the power supply: The internal resistance of the power supply refers to the resistance inside the power supply. If the internal resistance of the power supply is too high, the output current of the power supply will decrease when the load remains unchanged, resulting in insufficient current output.
2. Overload: If the power supply is overloaded, the output current of the power supply will decrease accordingly, resulting in insufficient current output.
3. Insufficient power supply driving capability: If the power supply's driving capability is insufficient, the output current of the power supply will also change accordingly when the load changes, resulting in unstable or insufficient current output.
4. Output filter capacitor failure: The function of the output filter capacitor is to filter out the AC component in the power supply output voltage, making the output voltage more stable. If the output filter capacitor fails, the power supply output voltage will be unstable, resulting in insufficient current output.
The following measures can be taken to address the above problems:
1. Replace with a power supply with one that has lower internal resistance.
2. Reduce the load.
3. Replace with a power supply with one that has stronger driving capabilities.
4. Replace the faulty output filter capacitor.
II. Troubleshooting Techniques for Switching Power Supplies with No Output
No output voltage from the switching power supply is also a common fault. The diagnosis method and steps for this fault are as follows:
The primary task in troubleshooting this type of fault is to determine whether the fault lies at the collector, base, or terminal of the switching transistor. The specific method is to measure the collector and base voltages of the switching transistor. Several possibilities exist:
(1) The collector voltage of the switching transistor is 0V, which is 1.4 times lower than the mains voltage. The switching transistor has no normal operating voltage. If the voltage is 1.4 times, it means that the collector voltage of the switching transistor is normal, and that the AC220V and the rectifier and filter circuit are working properly.
(2) The base voltage of the switching transistor is 0V (including the moment of startup). This indicates that the startup circuit is not providing a startup (conducting) voltage to the base of the switching transistor, or that the relevant components between the base and emitter are damaged. The startup circuit, the emitter of the switching transistor, and related components should be checked. If the voltage is between 0.6 and 0.7V (including the moment of startup), it indicates that the startup circuit, emitter, and components of the switch are normal. When the voltage is higher than 0.7V, it indicates that the startup circuit is normal, but the emitter junction of the switching transistor or its components are open or the resistance value has increased.
(3) The switching transistor meets the conduction conditions: the base voltage of the switching transistor is 0.6~0.7V, and the collector voltage is greater than 250V, indicating that the switching transistor meets the operating conditions. The fault occurs in the positive feedback circuit, including the positive feedback resistor, capacitor, freewheeling diode, and the positive feedback winding of the switching transformer and the connections between them.
III. Troubleshooting Techniques for Momentary Voltage Output in Switching Power Supplies
(1) Dummy load method (2) Measure whether the protection element is damaged (3) Disconnection method (4) Voltage reduction method. The first point that must be mentioned is the powerful load capacity of Minrong switching power supplies, which can be said to be achieved based on safety and pursuit. It can be said that Minrong switching power supplies have advantages such as high efficiency, high safety, and low loss, which are inseparable from Minrong's strong contributions. Similarly, the excellent load capacity of Minrong switching power supplies is inseparable from Minrong Electric's adherence to safety and pursuit of user needs.
Voltage reduction testing method for each functional circuit. After determining which part of the switching power supply is faulty using the above methods, the inspection methods for each part are as follows:
(1) Inspect the pulse width modulation circuit and the positive feedback circuit. There are two methods for replacing the electrolytic capacitor in the positive feedback circuit of the current switching power supply. One method is to replace the 0.016uF to 0.039uF capacitor, which has a very low failure rate and can be eliminated through inspection. The other method is to replace the 10uF electrolytic capacitor directly during the inspection.
(2) In the absence of an AC voltage regulator, for overvoltage protection faults, for safety reasons, you can first replace the vulnerable components in the circuit formed by the working voltage of the pulse width modulation circuit, namely the filter capacitor (from a few microfarads to 100uF electrolytic capacitor) to see if the switching power supply returns to normal.
