[sdiy] Comparator = Opamp ??

[harry]

Hail newbees!

Comparators are extremely fast... good for switching but not so good
with negative feedback as amplifiers.

Some comparators like the LM339 have an open collector output... so
they need a pull up resistor... and will switch to the negative rail in the low state.
The LM393 is the same.

The LM311 has a ground pin also... It needs a pull up resistor as well, but will
switch to whatever potential the 'ground' pin is at... somewhere between V+ and
V-  (don't HAVE to be ground)

All useful for converting analog voltages to digital levels... its a one or a zero.

Now some very fast op-amps can work as a pretty good comparator... and some
comparators can be an op-amp-of-desperation....

H^) harry

Peter van Hamersveld wrote:

> A comparator is a digital device that outputs a 'high' signal (logic 1 or about 4 to 5 Volts), when the voltage on the + connector is higher than the voltage on the - connector. If the one on the + is lower, it outputs a 'low' signal (logic 0 or 0 Volts).
>
> An Opamp has exactly the same appearance in schematics, though i get the impression (from Circuit Maker 2000 (simulation software)) that it behaves differently. Can anyone tell me the difference, or state that they infact ARE the same...
>
> tnx, thanks, tanx, thanx, tanks, tnks, thnks   (choose your favo-spelling)
> -- Peter van Hamersveld, plons at gmx.co.uk on 06-03-2001