W
Walter Harley
- Jan 1, 1970
- 0
So, before throwing out the plugboard, I decided to try the circuit again,
with resistors a few orders of magnitude smaller than before: the voltage
divider to the + input was a 10k and a 10R, the resistor from the - input to
ground was a 10k, and the feedback resistor from output to + input was
either absent, 100k, or 10k. And... it still oscillates. Now, I know
there are parasitic capacitances and inductances in that plugboard, but I
don't think they're THAT big.
So, I did more or less as Mac suggested, and threw the ST Micro TS393
comparator into the trash.
Then, I tried the circuit again using an LP339 from TI. This is a
micro-power CMOS comparator, like the TS393, but it's a different
manufacturer (and it's a quad rather than a dual). I built the circuit with
the original high impedances, with the voltage divider being 3.3M and 3.3k,
feedback of 3.3M, and the - input being 10M to ground. On the plugboard,
mind you.
No oscillation. Dead stable, no matter what I threw at it. Does exactly
what I want.
Conclusion: I threw out all my other TS393's, too. Yay, TI! Boo, ST Micro!
with resistors a few orders of magnitude smaller than before: the voltage
divider to the + input was a 10k and a 10R, the resistor from the - input to
ground was a 10k, and the feedback resistor from output to + input was
either absent, 100k, or 10k. And... it still oscillates. Now, I know
there are parasitic capacitances and inductances in that plugboard, but I
don't think they're THAT big.
So, I did more or less as Mac suggested, and threw the ST Micro TS393
comparator into the trash.
Then, I tried the circuit again using an LP339 from TI. This is a
micro-power CMOS comparator, like the TS393, but it's a different
manufacturer (and it's a quad rather than a dual). I built the circuit with
the original high impedances, with the voltage divider being 3.3M and 3.3k,
feedback of 3.3M, and the - input being 10M to ground. On the plugboard,
mind you.
No oscillation. Dead stable, no matter what I threw at it. Does exactly
what I want.
Conclusion: I threw out all my other TS393's, too. Yay, TI! Boo, ST Micro!