comparitor stability

[neo11]

Hey!

I am having difficulty stabilizing the output of a op amp comparitor in my circuit. As the positive input changes and approaches the reference voltage at the negative input, the output doesnt stay stable at a high state. The next device in my circuit which detects a high to low transition is picking up on every little change at the comparitor output.

Neo11

 

[nbucska]

The usual solution is to add a positive feedback i.e. feed a small portion of the output back to the non-inverting input. <nbucska@pcperipherals.com>

 

[biomedicalEng]

you must use a schmitt trigger to have a stable comparator
by using positive fidback.
if you dunno what is a schmitt trigger you can contact me
by this email address:

kasra_ravanbakhsh@hotmail.com

or see any electronic books!!!!

such as Integrated Electronics by Millman-Halkias
McGraw-Hill Book company

 

[nbucska]

using an Schmitt trigger as comparator may help but
adding an ST after the comparator doesn't. <nbucska@pcperipherals.com>

 

[Trex77]

Two types of hystersis to condider as a fix....

1. DC (using a feedback resistor to the positive input)

2. AC + DC (using a feedback resistor in parallel with a
feedback cap with a additional resistor in series
with the cap, to the positive input)

Selecting one of the two to give the best results will depend upon your noise levels, shielding, S/N ratio and input signal type (fast/slow level changes). As a hint the feedback resistor values are usually very large to allow only 0.01 to 1% feedback and the caps are usually very small to allow faster switching (10 to 220pF typ) the resistor in series with this cap is usually 1/4 to 4x the value of the input resistance that feeds the comparitor ckt.

Hope this helps...

 

[jbartos]

Suggestions:
1. Please, could you describe the hardware and application a little, e.g. is it analog or digital comparator, high or low speed, two variable or one variable and constant, differential voltage comparator, etc.
2. Visit

http://www.ti.com/sc/docs/psheets/diagrams/ontranl_a.htm

http://www-s.ti.com/sc/psheets/sboa081/sboa081.pdf

http://www-s.ti.com/sc/psheets/slcs...ch97cgi/s97_cgi?action=View&VdkVgwKey=http://

http://www-s.ti.com/sc/psheets/slcs...arator)+<IN>+Page),+[10](comparator)+<IN>+A)&

etc. for more info