Class D Audio Amp - IRS2092

Discussion in 'The Projects Forum' started by Skeebopstop, Oct 31, 2009.

  1. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
    358
    3
    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
     
  2. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    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.
     
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