How to carry out maintenance operations for switch mode power supplies, and what are the commonly used maintenance methods? Here are four methods for switch mode power supply maintenance, including short circuit method, false load method, etc. Let's understand together.

Four Methods for Maintenance of Switching Power Supply

There are three methods: short circuit method, series bulb method, false load method, and exchange method.

1. Short circuit method

The switching power supply of LCD displays mostly uses a direct sampling and stabilizing control circuit with a photoelectric coupler. When the output voltage is high, a short circuit method can be used to distinguish the defect range.

2. Series light bulb method

The series light bulb method refers to removing the fuse of the input circuit and using a 60W/220V light bulb to string at both ends of the fuse. After applying communication voltage, if the light bulb is very bright, it indicates that there is a short circuit in the circuit. A light bulb has a certain level of resistance, such as a 60W/220V light bulb, which has a resistance value of about 800n (referring to thermal resistance), and the light bulb plays a certain role in limiting current.

One is that the brightness of the light bulb can be visually used to roughly determine the defects of the circuit, and the other is that the current limiting effect of the light bulb does not immediately cause the short circuited circuit to burn out the components.

After cleaning the short circuit defect, the brightness of the bulb will decrease, and then the bulb will be removed and fused.

3. False load method

When repairing a switching power supply, in order to distinguish whether it is a defect in the load circuit or a defect in the power supply itself, it is often necessary to disconnect the load and add a false load to the output terminal of the switching power supply (usually 12V) for testing.

Choosing to connect a fake load is because during the cut-off period of the switch tube, the energy stored in the primary winding of the switch transformer needs to be released to the secondary. If the fake load is not connected, the energy stored in the switch transformer has nowhere to be released, which is prone to causing breakdown damage to the switch tube.

Regarding the selection of fake loads, it is common to choose a 30-66W/12V light bulb (used on cars or motorcycles) as a fake load. The advantage is that it is intuitive and convenient. Based on whether the light bulb can emit light and the brightness of the light, it can be determined whether the switch power supply can have voltage output and the up and down of the output voltage.

To reduce the initiating current, a 30W soldering iron or a high-power 600Q-1kn resistor can also be used as a false load.

4. Exchange method

In the switching power supply of LCD displays, a power control chip is commonly used, and this type of power control chip is cheap for ten people.

Therefore, when it is estimated that there is a problem with the power control chip, one can consider using the exchange method to replace it.