[sdiy] Sequencer good (and bad) news update

[Ian Fritz]

Hi Harry (et al.) --

Thanks for the further clarification. I never used the LM324 single-supply 
before my recent project, so I'm glad to learn about potential booby traps.

My system does, in fact, have two comparator circuits. Since I was picking 
thresholds off a somewhat noisy source, they both were designed with a bit 
of hysteresis. Maybe this is the difference in our results!

Circuit 1 is a follows:
+ input pin through 3.3k to signal source and through 150k to output pin 
(positive feedback)
- input pin to junction of 39k/1k voltage divider between PS and gnd. (0.16 
V threshold ref.)
output pin through 3.3k load resistor to gnd.
Quiescent output voltage is 0.5 mV. (Yes, half a millivolt.)

Circuit 2 (inverting comparator):
- input pin directly to signal (another 324's output)
+ input pin through 100k to ref. voltage (consisting of a voltage divider 
and a cap.) and through 4.7M feedback resistor to output pin.
output pin to 3.3k load
Quiescent output voltage is 0.9 mV.

I vaguely remember having trouble running comparators open loop, but I 
don't recall exactly what the problem was.

We still haven't heard back from Tony as to how he got a 1.2 V saturation.  :)

   Ian


At 08:21 PM 4/18/2002, harry wrote:

>Hmmm... My  application was used as a comparator... so I would
>have expected it to work quite well near ground as well. I don't think
>the 500mV was offset voltage ???
>
>How light was your load ?   Mine was fairly heavy (like 2mA)
>
>H^) harry