[sdiy] LM311 woes

[Ian Fritz]

Thanks,Paul.

I thought I was being fairly careful with the design and layout, but I'm 
sure it's not perfect.  Input impedances are under 5k.  PS bypassing is 
within 1 cm of the pins.  Circuit is over a ground plane.  Inputs and 
outputs run in opposite directions (except for a hysteretic feedback 
cap).  Input R's are close to the pins.

I haven't been able to see any oscillations.  The symptoms are that the 
output is high when it should be low!  (-)In = -2.2V, (+)In = -2.6V, Out = 
(+) rail.  Just sits there!

Is it possible that the new units slew faster?  Perhaps a switching spike 
could then knock the device into latchup?  I didn't see anything about that 
in the data sheet.

Ian


At 07:06 PM 1/27/2009, Paul Perry wrote:
>I think the problem relates to the fact that the open loop gain of any
>comparator is very high. And so is the input impedance, and so stray
>capacitances are much more critical in comparator circuits than (for
>example) audio frequency amplifiers etc.
>I must say, I have had more grief with comparator circuits than anything
>else..
>At a guess the 'new' comparators have more gain & are oscillating.
>
>paul perry Melbourne Australia
>
>
>_______________________________________________
>Synth-diy mailing list
>Synth-diy at dropmix.xs4all.nl
>http://dropmix.xs4all.nl/mailman/listinfo/synth-diy