[sdiy] LM311 woes

[cheater cheater]

Just to get this out of the way..
but maybe this one doesn't have the smoke anymore?

On Wed, Jan 28, 2009 at 2:35 AM, Ian Fritz <ijfritz at comcast.net> wrote:
> 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
>>
>>
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