Common reasons for howling switching power supply (1)

News     |      2021-10-11 10:34

Abstract: Switching power supply controls the time ratio of switching on and off in the circuit. Maintain a stable circuit voltage output. This is a very common power supply design. But those who have been engaged in the design of switching power supply know that they often hear some whistling sounds during the testing of the switching power supply. It is similar to the leakage sound when the high voltage is bad, or the sound like the high voltage arc. So when these phenomena appear, how should they be resolved?

 

table of Contents:

1. Poor varnish dipping of transformer

2. The PWM IC grounding wiring error

3. Misalignment of optocoupler operating current point

4. The ground wire of the reference voltage regulator IC TL431 is faulty

 

Generally speaking, the reasons for the howling of Switching power supply generally have the following inducements. Here we will introduce six causes of howling in the Switching power supply and provide corresponding solutions to these six causes.

 PCB components

1. Poor dipping varnish of transformer

Including unimpregnated Van Lishui. The howling causes sharp spikes in the waveform, but generally, the load capacity is normal. In particular, the greater the output power, the stronger the howling, and the lower power may not necessarily be obvious. A 72W charger product has the experience of overloading and poor loading, and it is found in this product that there are strict requirements for the material of the PCB components magnetic core. One thing to add is that when the design of the transformer is poor, it may also cause abnormal noise due to vibration during operation.

2. The PWM IC grounding wiring error

Usually, some products can work normally, but some products cannot be loaded and may fail to vibrate. Especially when some low-power IC (PCB components) are used, they are more likely to fail to work normally.

 

3. Misalignment of optocoupler operating current point

When the position of the optocoupler’s working current resistance is connected before the second filter capacitor, there is also the possibility of howling, especially when the load is more.

Switching power supply

4. The ground wire of the reference voltage regulator IC TL431 is faulty

The grounding of the same secondary reference voltage regulator IC and the grounding of the primary IC have similar requirements; that is, they cannot be directly connected to the cold and hot ground of the PCB components transformer. If they are connected together, the result is that the load capacity is reduced, and the howling sound is proportional to the output power.