After the switching power supply is damaged, most of them can be repaired independently. All the loads are disconnected. A 22V, 100W light bulb is placed on the main load power supply as a dummy load, and a low-voltage power supply safety method is adopted. The coupling transformer is reduced to about 70V for maintenance. This maintenance method completely avoids the phenomenon of damaging the components again due to hidden dangers in the circuit. Generally, a normal switching power supply (parallel type) can start to vibrate normally at a power supply voltage of about 70 V. work, and slowly adjust the output voltage of the autotransformer. The output voltage of the switching power supply should be fixed at its preset voltage value. If the output voltage of the switching power supply changes with the change of the input voltage, it indicates that its voltage regulation Part of the problem; if there is no voltage output, it means that there is a problem with the oscillator circuit.
The first case: We take the parallel optocoupler controlled regulated switching power supply as an example to discuss its maintenance method. When the switching power supply cannot be regulated normally, the first step is to confirm the fault-causing part. The simple and quick method is: short-circuit the two control pins of the hot ground end of the optocoupler. If the circuit enters the vibration-stop state, it indicates that the fault is sampling. Comparison circuit, sampling comparison circuit problems are mostly caused by the damage of the comparison IC and the optocoupler (most of the damage of the comparison IC will cause the photocoupler to be damaged at the same time). Pay attention to the parameters of the transistor.
The second case: the circuit does not vibrate. When you are sure that the power supply voltage is normal, first check whether the start-up resistance (that is, the resistance connected between the 311V power supply and the base of the main vibration power tube) is open circuit or changing value, and also consider whether the non-vibration is caused by the action of the protection circuit. Caused, such as the 6th pin voltage of STR6309 (normally 0 V), the 5th pin of STR50213 (about 100V when normal), the 3rd pin of TEA2261 (normally 0V), the 5th pin of TDA4601, etc., if it is a protection The vibration stop caused by the circuit can be judged by this point. In addition, when there is a problem with the control circuit (such as the breakdown of the control tube), the circuit vibration will also be stopped.
