×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

comparitor stability

comparitor stability

comparitor stability

(OP)
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

RE: comparitor stability

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>

RE: comparitor stability

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

RE: comparitor stability

using an Schmitt trigger as comparator may help but
adding an ST after the comparator doesn't.

<nbucska@pcperipherals.com>

RE: comparitor stability

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...

RE: comparitor stability

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources