Double comparator with delay gives more accuate trip?

[cupoftea]

Hi,

My sincere apologies, i meant to put this in the Analog Electronics section.

Do you agree that this “double comparator with delay” method is superior to just a single comparator with hysteresis?
The trouble with a “single comparator with hysteresis” is that the up-going and down-going trip points are too different. The double comparator method shown, allows up-going and down-going trip points to be pretty much the same.
There is some delay in the trip, but very often you do not care about this.

So why is this method not more used?

 

[FvM]

Used to achieve what? You don't tell which problem should be solved with this circuit.

 

[crutschow]

So why is this method not more used?

Because, unless you really need the up and down trip points to be identical (which is often not the case), then it just adds unnecessary complexity.

 

[cupoftea]

Thanks, need to charge supercap up to 2.4V......as close as possible...will be inconvenient having much hysteresis....eg, if it charges up to 2.4V....then discharges down to say 2.1v before it starts charging again due to the hysteresis...that would be bad.

 

[mtwieg]

Do you agree that this “double comparator with delay” method is superior to just a single comparator with hysteresis?
The trouble with a “single comparator with hysteresis” is that the up-going and down-going trip points are too different.

Different applications call for different amounts of hysteresis. The thresholds can be arbitrarily chosen with component selection.

The double comparator method shown, allows up-going and down-going trip points to be pretty much the same.
There is some delay in the trip, but very often you do not care about this.

So why is this method not more used?

Ok so it's a comparator with some hysteresis followed by a delay/debouncing circuit. Maybe useful in some applications, but certainly not a general replacement for a simple comparator with hysteresis.

 

[cupoftea]

Ok so it's a comparator with some hysteresis followed by a delay/debouncing circuit. Maybe useful in some applications, but certainly not a general replacement for a simple comparator with hysteresis.

Thanks, as you know, the double comparator doesnt have jittering at the actual output. So would be better than a comparator with hysteresis you would think...just that it has the delay, and of course, uses two comparators.
The first comparator my jitter, but who would care.

 

[FvM]

Thanks, as you know, the double comparator doesnt have jittering at the actual output. So would be better than a comparator with hysteresis you would think

It may well have "jittering" (arbitrarily varying output), depending on the input signal. The problem is, that you are apparently presupposing specific parameters of you application, assuming they are common to all comparator applications and proposing circuit implementations based on this narrowed perspective.

I agree with the analysis by mtwieg.

 

[BradtheRad]

I chose a single op amp with hysteresis, when constructing my homebrew charge controller for my solar panels and batteries. I thought I was being clever, keeping a low parts count. But I was not clever.

The range of hysteresis was only a couple volts (for a 24V system). I took a long time adjusting the levels of charge-On-charge-Off. It was tedious because it involved turning one pot, waiting to see the effect, then turning a second pot and waiting to see the effect. Then repeat. Etc.

I should have gone for a window comparator using two op amps. That makes it easier by setting just one voltage threshold per op amp.