I have a question for you. I made a buck circuit, but the inductor whistles when it is loaded. What is the reason?

MartinFowler

I have a question for you. I made a buck circuit, but the inductor whistles when it is loaded. What is the reason? [Copy link]

As shown in the figure below, after reducing the 35V voltage to 28V output and adding 158 voltage feedback, it will howl when loaded. If it is not added, it is normal. I don't know what the reason is.

maychang

There is something wrong with the component values in this figure.

The internal reference voltage of LMR14050 is 0.75V. If R17 is 510 kilo-ohms and R19 is 12 kilo-ohms, the output voltage should be 0.75/(12/(510+12))=32.6V.

maychang

The purpose of adding RS2 and LM158 (U6A) is obviously to limit the current. However, the voltage across RS2 should be compared with a reference voltage to limit the current. After adding LM158 (U6A), which voltage is the voltage across RS2 compared with? From the figure, LM158 (U6A) works in an open loop and is not compared with any voltage.

maychang

As for the U6B below, I don't know what the OP means.

Where did the OP's picture come from?

qwqwqw2088

If it is normal without adding, what is normal?

The howling is caused by the self-excitation of the inductor.

What is the output of 158 connected to?

qwqwqw2088

The switching frequency of the LMR14050 chip is very high. The device routing layout and inductor selection are very critical. Nothing is explained.

How much load does it start to call?

木犯001号

Increase EC4 and reduce or remove EC5

The current sampling resistor is too small, so direct comparison is not suitable. Use dual op amps to amplify all the way and then compare.

不亦心

maychang posted on 2020-5-27 14:56 The purpose of adding RS2 and LM158 (U6A) is obviously to limit the current. However, the voltage across RS2 should be compared with a reference voltage to limit the current. Floor...

There is a Ref2.5V reference, CC/CV

不亦心

The loop is not adjusted properly. It will be easier to adjust if the op amp is changed to negative logic control.

maychang

Bu Yixin published on 2020-5-29 21:55 There is a Ref2.5V benchmark, CC/CV

Yes. I missed it. There is a 2.5V voltage, divided by 1%.