Simple Op Amp Selection

[fantasymick]

Hi, I'm looking to boost a signal from ~1V to 5V to trigger a function generator, which will then generate a pulse in burst mode. It's currently not triggering at all because of the low voltage of my input signal, which is a saw tooth waveform, 1V peak to peak, that repeats ~100Hz. Can someone recommend a general purpose op amp for this purpose?

I plan to build something similar from this site:
**broken link removed**

Thanks,
Michael

 

[Torben]

Hi, I'm looking to boost a signal from ~1V to 5V to trigger a function generator, which will then generate a pulse in burst mode. It's currently not triggering at all because of the low voltage of my input signal, which is a saw tooth waveform, 1V peak to peak, that repeats ~100Hz. Can someone recommend a general purpose op amp for this purpose?

I plan to build something similar from this site:
**broken link removed**

Thanks,
Michael

Hi Michael,

What supply voltage do you have available?

Any general-purpose op-amp should easily be able to handle your job. I've got a whole whack of ancient LM358s and I'd be tempted to use one of those if I was building this thing, just to try to use one up. And it'd only use half of it. Or maybe an old 741 or something. Normally I don't think anybody would recommend these old beasts for anything anymore but they should have no problem with your job. If you want better op-amps for about the same price you could try a TL071 or TL081.


Good luck,

Torben

 

[fantasymick]

I am thinking about powering it from a 12V AC adapter. I think all of these op amps require a +/-ve voltage supply. Is there a model, or do you know any circuit setup that I can use that needs only one power supply for my application?

Thank you for the suggestions. You can tell I'm not too familiar with circuits. I guess I kind of want something that just works.

Michael

 

[audioguru]

Any opamp will operate from a single polarity supply if you bias its inputs correctly.
A few opamps have an input and an output that still work at the negative supply voltage which is 0V if there is only one supply.

 

[Torben]

Hi Michael,

Check the sticky message Dual or single supplies for opamps in General Electronics Chat. Audioguru made a diagram showing how to connect op-amps for either dual or single supplies.

If you have any questions ask away. It's also been covered a few times already so searching the forums should turn up some existing explanations.


Good luck,

Torben

 

[fantasymick]

Thanks, I will search more carefully next time.

I think with the given single supply circuit, the output voltage from 0V would be 6V? (Correct me if I'm wrong) Since I want the output to vary between 0 and 5V, maybe I do need a -ve supply. Would this chip work?
**broken link removed**

It seems like a simple solution.

Thanks,
Michael

 

[ericgibbs]

hi Michael,
Since your function gen dosn't 'see' the 1v saw tooth tigger, a simple single supply opa would do fine.
If you power say a LM358 from +6V, the output will limit at about +0.5V thru +5V anyway.

As Torben suggests, at 100Hz, a LM358 is an inexpensive choice.

A point to measure, is the driving sawtooth referenced to ground.?

That is, does it swing +/- about the 0V line or is it referenced above 0v.?

What form does the FG trigger input expect, eg: fast edge or will it accept a slow sawtooth.?

Is it important on which part of the sawtooth the FG triggers.?

The reason I am asking so many damn questions, you may require a comparator that generates a 'edge or gating pulse' to the FG, rather than an amplified saw tooth.

Hope you follow this..

 

[fantasymick]

Appreciate all the advices. I got the triggering working with a simple voltage regulator (LM311) after reading more about it. With a POT, there's the added advantage of this setup for setting where during the sawtooth I would like the trigger to happen.

Thanks,
Michael

 

[ericgibbs]

Appreciate all the advices. I got the triggering working with a simple voltage regulator (LM311) after reading more about it. With a POT, there's the added advantage of this setup for setting where during the sawtooth I would like the trigger to happen.

Thanks,
Michael

hi,
For future reference a LM311 is a Comparator, not a Voltage regulator.