Electronics > Beginners
What's the use of OpAmps?
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Darkwing:
Apart from the hijackers: thank you very much guys!  :)  ;D

The linked PDF book is a very good read, I like  that! Must read more.  8)

I understand for now, that such an OpAmp is a very flexible signal amplifier and in terms of "manufacturing tolerance" and reliability and signal quality to prefer, instead of simple BJTs.

But what I don't understand is: can they drive loads? Are they suitable for "the power stage" of a project? It doesn't seem so. I would be interested, if someone could point me to a part what I would then call an "OpAmp Driver", that can handle bigger loads.

(Maybe that's why I never saw a use for them in any of my projects so far, because I understand 'amplification' as being able to 'amplify voltage AND current'. [A MOSFET with 1.4mΩ Rdson is not even slightly impressed, when there's a current of 5A or so ... would an OpAmp be?])


However, you guys helped me a lot! Thanks!  :-+
IDEngineer:

--- Quote from: Darkwing on May 01, 2019, 08:23:03 pm ---can they drive loads? Are they suitable for "the power stage" of a project? It doesn't seem so.
--- End quote ---
There used to be "power opamps" available. Apex made some that could drive multiple amps, came in suitable heaksink-able packages, etc. I don't know if Apex is even still around anymore.

Generally opamps are used for the small-signal part of the signal chain. Then it's common to see a discrete power transistor stage driven by an opamp. Many opamps have enough output current to drive power transistors, at least the first stage, and if you need even more power you cascade another discrete power amplifier stage after the first one, with the latter acting as a preamp for the former.

Stated differently: You'd use opamps to do small-signal amplification, filtering, and other signal conditioning. Then, once the signal has been manipulated the way you like, you use power transistors as a final to get the voltage and/or current you need to drive the load.

EDIT: Apex is still around! https://www.apexanalog.com/  I see they have output currents to 50A and voltages exceeding 350V. Most likely they are simply encapsulating my above description, a traditional opamp with a discrete power final. But it is nice that they make them available in a ready-to-go package.
Darkwing:
Ok, thanks for clarification!  :)


Btw: Apex PA75CD Power Op Amp 40 bucks!?  :wtf:

Oh boy ... and that's their entry level ... This must be a nery niche product I promise to never use!  :-DD
IDEngineer:

--- Quote from: Darkwing on May 01, 2019, 09:02:35 pm ---Btw: Apex PA75CD Power Op Amp 40 bucks!?  :wtf: Oh boy ... and that's their entry level ... This must be a nery niche product I promise to never use!  :-DD
--- End quote ---
Yep, they're very proud of them, but Apex has been around for a very long time so they're selling them to someone.

They'd be useful for one-offs where you didn't know how craft your own, or your focus was on some other part of the device and you just wanted a quick solution, etc. For example, I've always thought they'd be a quick fit for a galvanometer amplifier. I'm sure there are other applications, and their continued existence seems to confirm that.
free_electron:
there's many more power opamps. open any kind of surround sound amplifier these days and you will find plenty of TDA , STK  and other series opamps.

i personally like the ICEPOWER opamps. :) no analog muckery.
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