×
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

Comparator with constant offset

Comparator with constant offset

Comparator with constant offset

(OP)
I'm working with two voltage levels where I need a comparator to switch when the difference between the two pass 100 mV.
Problem is, the common-mode voltage varies, so I can't make the offset between the two inputs using resistors.

One voltage is DC, the other is 16 kHz pulses.

Can anyone point me in the right direction?
Do comparators exist with built-in constant offset?
Or can you suggest a different way of "injecting" 100 mV into one input?

BTW, supply voltage is 12 V, the signal is somewhere in between.

Thanks,

Benta.
 

RE: Comparator with constant offset

"...when the difference between the two pass 100 mV..."

Is that difference in both directions? In other words, 100mV of hysteresis? If so, then easy (?).

 

RE: Comparator with constant offset

(OP)
No, not hysteresis, rather pure DC offset.
But it must be the heat affecting me...
A summing amplifier before the DC input to the comparator can of course add the 100 mV offset.
As usual, this came to my mind when driving home from work (emptying your brain suddenly brings solutions, which is why it's important to take a 5...10 min break regularly).

Thanks for replying, sorry I wasted your time.

Cheers,

Benta.
 

RE: Comparator with constant offset

smile
 

RE: Comparator with constant offset

You can also just add the offset directly to one of the comparator inputs.  Say the the positive side would normally be grounded, instead have it go to your offset voltage.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Comparator with constant offset

(OP)
itsmoked:
No, the problem is exactly the varying common-mode voltage. None of the inputs are ground or positive referenced.
Anyway, I've solved it now.

Cheers,

Benta

RE: Comparator with constant offset

Glad you solved it, I'll share this anyway, it may come in handy for someone some day...

Depending on the application, another way to do this is by intentionally unbalancing the input.  For example the LM311 comparator has two balance inputs which can vary the input offset over a modest range.

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