Comparator vs. OpAmp: pros & cons?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I was thinking about a more complex follower driven from the voltage of a small capacitor. This capacitor would be either charged or discharged through complementary current sources activated by the classic rail threshold comparator.

This is efficient while still feeding little content to the output through the C-B capacitance.

For a worst-case +-150V design the maximum required slope would be just 10V/us, much smaller than the 3KV/us slopes usually found in off-line SMPS. Note that the amount of EMI generated is proportional to these slopes, as switch dissipation is, though...
 
Hi all,

Going back:

Joseph Hynes said:
are there any advantages to using a hi-speed comparator vs a high-speed opamp connected as a comparator?

No one seems to have mentioned that some op-amps go crazy when their input differential voltage gets "too large", i.e. phase reversal of the output, if I recall right; comparators are designed not to do this...

Cheers!!

Clem
 
maybe it's a OT, but I am using LM393 and I need your help:
I want to build if-sound-comes-then-led-flash "unit".

It is like a detector: if a sound comes out from my PC-s soundcard, comparator must detect it and at the same time flash LED in the comparators output.
Sensitivity could be adjustable.
And one more thing: I want to effect, that if the signal comes for a short time, then the led should not only flash but burn for about 4 secs(or more).
Power supply is +15V.

Can I realize all this?

Thanx!
 
The '393 should be fine - you'd want to configure it as a window comparator, which can easily be done since the '393 is a dual. Capacitor-couple the signal in and pull it to some "middle" voltage. Then, configure one stage to trigger when the input exceeds a certain threshold in the positive direction, configure the other one in the opposite direction.

Parallel the outputs and connect to a one-shot to give you the 4-seconds or more 'flash'.

Cheers!
 
I can think of a way that MIGHT work with just one comparator, but it would require playing around with the values and it would be much more messy. Also, you'd have to choose which signal excursion polarity you'd want to trigger on. That's probably an acceptable compromise. I'll try to draw out something and post it when I get to the office tomorrow... :)

Cheers
 
Hi peranders,

Agreed if you want to trigger on the basis that the input signal may be going "up" or "down" compared to reference "no signal", you'd definitely need two. But if you assume that 'eventually' the signal (since it's an AC, even often assymetric) will cross-over to the other polarity and trigger, wouldn't it be OK to do it with just one?

What I find messy is to get a time constant of 4sec with just one comparator - sounds like a job for high-capacitance with positive feedback on the reference voltage of the comparator....

Cheers!
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.