IRS2092S sounds like a tea kettle

Hello

This is my first class D build and it's giving me some issues.

With no input signal and a speaker attached, it will give me a siren/tea kettle sound.

If I input a 40hz tone to the amp, then looking at the output (with speaker connected), it looks like the upper half of the sine wave is not rising correctly, the lower half looks ok?

Looking at the output of the MOSFETs before the LC filter, with no signal input, I do get R-R oscillation but it is in what appears to be pulses. Is this normal? Or should it be continuous.

Another thing I noticed is that the more volume I give the amp, I see the V+ rail start climbing. My rails are +/- 54V, positive rail will climb to 77V whereas the negative rail will stay around 54V give or take a few tenths. When the positive rail hits ~77V the amp will start making a popping sound. If I decrease or remove audio, the positive rail will fall back to 54V and it will stop popping but continue making a tea kettle noise.

I've attached some scope images and schematic.

Note: In the schematic I made a mistake for VCC 12V power. It is referenced to ground. In the actual circuit I am using another power supply referenced to V- rail to VCC. I am also only using 1 pair of output FETs at the moment.

Thanks
 

Attachments

  • irs2092s_sch.PNG
    irs2092s_sch.PNG
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  • Output to speaker with 40HZ input.jpg
    Output to speaker with 40HZ input.jpg
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  • Yellow - Output before LC, Purple - Output to Speaker.jpg
    Yellow - Output before LC, Purple - Output to Speaker.jpg
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