Diagnostic methods for abnormal switching power supply voltage output
The primary task of troubleshooting such faults is to determine whether the fault is located at the collector, base, or switching transistor. The specific method is to measure the collector and base voltages of the switching transistor. There may be the following situations:
(1) The collector voltage of the switching transistor is 0V, which is 1.4 times lower than the mains voltage. The switch tube does not have a normal operating voltage. If the voltage is 1.4 times, it indicates that the collector voltage of the switch tube is working normally, and the AC220V and rectifier filter circuit are working properly.
(2) The base voltage of the switching transistor is 0V (including the start-up time). This indicates that the starting circuit did not provide starting (conductive) voltage to the base of the switch tube, or that the related components between the base and emitter were damaged. The starting circuit, switch tube emitter, and related components should be inspected. If the voltage is between 0.6 and 0.7 (including the moment of startup), it indicates that the starting circuit, emitter, and components of the switch are normal. When the voltage is higher than 0.7V, it indicates that the starting circuit is normal, but the emitter junction or its components of the switch tube are open or the resistance value increases.
(3) The switching transistor has conductivity 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 has working 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, as well as the connection board between them.
Maintenance Techniques for Instantaneous Voltage Output of Switching Power Supply
(1) False load method (2) measures whether the protective components are damaged (3) disconnection method (4) voltage reduction method. The first point that cannot be ignored is the powerful load capacity of the civilian melting switch power supply, which can be said to be achieved based on safety and pursuit. It can be said that the civilian melting switch power supply has advantages such as high efficiency, high safety, and low loss, which cannot be separated from strong contributions. Similarly, the high-quality load capacity of Minrong Switching Power Supply is inseparable from Minrong Electric's commitment to safety and pursuit of users.
Voltage reduction detection method for various functional circuits. After determining which part of the switch power supply is faulty through the above methods, the inspection methods for each part are as follows:
(1) Check the pulse width modulation circuit and positive feedback circuit. There are two methods for replacing electrolytic capacitors in the positive feedback circuit of current switching power supplies, one is 0. 016UF0. The fault rate of 039uf capacitor is very low and can be eliminated through maintenance. Another type is an electrolytic capacitor with a capacitance of around 10uF. This capacitor can be directly replaced during maintenance.
(2) In the absence of an AC voltage regulator, for overvoltage protection faults, for safety reasons, the vulnerable parts in the circuit formed by the working voltage of the pulse width modulation circuit, namely the filtering capacitor (electrolytic capacitor ranging from a few microfarads to 100uF), can be replaced first to see if the switching power supply returns to normal.
