Help with the feedback control loop of the flyback switching power supply

西里古1992

Help with the feedback control loop of the flyback switching power supply [Copy link]

In the picture, the feedback control loop of the reference voltage chip based on TL432, 1 is the sampling circuit, 2 is the feedback loop, what is 3 and what is its function?

PowerAnts

Search for Type I, II, III compensators by yourself

西里古1992

PowerAnts posted on 2020-5-19 11:42 Search for type I, II, and III compensators

Master, this is a 68W flyback switching power supply based on LM5021 that I am testing. The problem now is that when the load exceeds about 40W and the input voltage exceeds DC300V, the current sampling waveform detected by R62 and the MOS tube driving waveform begin to become gradually disordered, the transformer makes a sizzling sound, and the output voltage drops below 12V and close to 11V. I guess the resistance value of R62 is not selected properly, because changing the resistance value does cause different abnormal situations each time. This problem will not occur above 0.4Ω, but the sampling value is too large, causing the start-up voltage to even reach DC200V before starting. If the resistance is selected below 0.4Ω, there will always be problems with disorder and abnormal noise. What is the most likely reason for this?

西里古1992

PowerAnts posted on 2020-5-19 11:42 Search for type I, II, and III compensators

Master, I used a fan to blow on the MOS tube and the rectifier tube this afternoon, and found that it was much better. When the load reached 50W, it output about 12V stably. When the fan was turned off, the previous phenomenon occurred. It stopped working when the load reached 90%. Is the heat dissipation not done well? Here are the temperature data of the MOS tube and the rectifier tube, which are also in the specification.

PowerAnts

You should focus on understanding the three types of compensators, and design them according to your own topology and working mode. Don't pile up circuits randomly.

maychang

PowerAnts posted on 2020-5-20 08:55 You should focus on understanding the three types of compensators, and design them according to your own topology and working mode. Don't pile up circuits randomly

The original poster doesn't even know what the resistor connecting the source of the MOS tube to the ground (R62 in the picture on the third floor) is used for (otherwise it wouldn't be changed back and forth between 0.4Ω and 0.4Ω). How can he understand the relatively complex issue of feedback compensation?