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Half-Bridge 0-30V, 0-20A Feedback loop problem

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paladyn:
xavier60

If I did not write about R1, I'm sorry, I had to forget.

I did a few tests, I tried without R1 resistor and with a few hundred ohms and with very large> 20KOhm but each time the effect was much worse than the calculated resistor

I think I know why the transformer is squeaking but I do not know why this is happening. I checked the symmetry of the pulses on the primary side of the transformer using an oscilloscope and I came to the conclusion that the transformer lost pulse symmeters. Sometimes, 260us are missing the upper half of the pulses while there are impulses at the bottom. Of course, my Rigol 1074Z oscilloscope does not allow very accurate measurements.

It seems to me that when there is a lack of impulses, then it may come to sub-mapping the core. The only question is why SG3525 allows such behavior?

xavier60:
I tested mine. The SG3525 can't output pulses shorter than 600ns.
When a very low duty cycle is needed, it skips pulses. Sometimes randomly, making a hissing sound. Other times there it is a regular pattern causing a small squealing sound. The drive stays mostly symmetrical.
Actually I prefer that the IC does this instead of outputting needle like pulses.

paladyn:
Add simulations in the LTSpice SG3525 in the enclosure along with a feedback loop. According to the simulation, everything is ok, but in reality it is not.

MagicSmoker:

--- Quote from: paladyn on June 17, 2019, 10:37:44 am ---Add simulations in the LTSpice SG3525 in the enclosure along with a feedback loop. According to the simulation, everything is ok, but in reality it is not.

--- End quote ---

Sigh... See my post #16. When SPICE says your circuit works fine but the real world shows it most certainly does not then the difference is in the parasitics (stray C and L) and layout.

xavier60:
Output ripple should  only contain 80Khz. A small amount of this getting to the PWM compactor shouldn't cause a big problem.
If 40Khz gets in, then it will cause a big problem.
It can be difficult getting output voltage from the output capacitors to the input of the error amp without picking up interference.
I suggest getting the voltage from the output capacitors to the input of the error amp through a temporary common mode choke.
Try a 10 turn or more bifilar winding on a core from a mains hash choke.

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