How to perform maintenance operations on switching power supplies and what are the commonly used maintenance methods. Here are four methods for maintenance of switching power supplies, including short circuit method, false load method, etc. Let’s understand them together.
Four methods for switching power supply maintenance
The first is the short circuit method, the second is the series light bulb method, the third is the false load method, and the fourth is the exchange method.
1. Short circuit method
Most of the switching power supplies of liquid crystal displays use direct sampling voltage stabilizing control circuits with photoelectric couplers. When the output voltage is high, the 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 from the input circuit and stringing a 60W/220V light bulb across both ends of the fuse. After the AC voltage is applied, if the light bulb is very bright, it means there is a short circuit in the circuit. The light bulb has a certain degree of resistance. For example, a 60W/220V light bulb has a resistance of about 800n (referring to thermal resistance). The light bulb plays a certain current limiting role.
First, the circuit defects can be roughly judged intuitively through the brightness of the light bulb. Second, the current limiting effect of the light bulb will not immediately burn out the components of the short-circuited circuit.
After cleaning the short circuit defect, the brightness of the bulb will dim, then remove the bulb and install the fuse.
3. False load method
When repairing the switching power supply, in order to determine whether it is a defect in the load circuit or the power supply itself, it is often necessary to disconnect the load and add a dummy load to the output end of the switching power supply (usually 12V) for testing.
The reason for choosing to connect a false load is that during the cut-off period of the switching tube, the energy stored in the primary winding of the switching transformer will be released to the secondary. If a false load is not connected, the energy stored in the switching transformer will have nowhere to be released, which will easily lead to breakdown of the switching tube. damage.
Regarding the selection of dummy load, generally 30-66W/12V light bulbs (used in cars or motorcycles) are selected as the dummy load. The advantage is that it is intuitive and convenient. Based on whether the light bulb emits light and the brightness of the light, you can know whether the switching power supply has voltage output. and the output voltage up and down.
In order to reduce the startup current, you can also use a 30W electric soldering iron or a high-power 600Q-1kn resistor as a dummy load.
4. Exchange method
In liquid crystal display switching power supplies, a power control chip is generally used, and such power control chips are very cheap.
Therefore, when it is estimated that there is a problem with the power control chip, you can consider replacing it with the replacement method.
Post time: Mar-25-2024