Hey all,

I've just fired up my class D audio amp design for the first time using the IRS 2092 (great little chip from international rectifier). I have attached the IRS2092 equivalent circuit.

Vaa/Vss ~= +4V/-4V.

I see the COMP pin happily bouncing between +4V and -4V seemingly in modulation to my input audio signal, as would be expected (~100-200kHz). This implies to me the integrator is working fine.

The problem comes in because the output "LO" gate drive signal never bothers to come on. I have confirmed Vcc is +12V to COM, so the UVLO circuit shouldn't be active. The only thing I could think of was the lo side over current protection, however that wouldn't be activated until it at least tried to drive once (as it is in synch with a 'high' on "LO" and sensing the Vds of the low side fet) and with this type of current sensing it will just keep retrying and being interrupted, so I should at least see activity.

I just thought I might be over looking something stupid and you all could help. The high side error protection is abstracted from the low side, so I am currently only focusing on the fact I never see a pulse on "LO" ever.

Regards,

James

 

The 2092 is a minefiled for those new to class d.
High speed high current switching is a minefield.

I found I needed 100nf across b+/b-, b+/gnd and b-/gnd.
The VCC rail needs 100uf on it.

I found mine was fussy about the inductor, the recommended 22uh made the 2092 reset quite early before clipping. I found winding my own inductor of 30uH was much better.