Humongous Op-Amps - Electronic Circuits Projects Diagrams Free

dknguyen · 28th December 2006, 07:43 AM

So it never occured to me that there existed ginormous op-amps that are capable of driving motors since all I have ever seen are the little IC things that amplify mA signals. I was looking at a link for a motor controller IC that someone asked about on the forum and their example circuit and it just had this measly little op-amp on the circuit driving what I assumed to be a motor. So I looked up this op-amp and it was huge! 10A! And then I looked into it more and found humongous 50A+ op-amps. I guess it never occured to me that people would scale up the op-amps I normally see to do these things.

I also found switching amplifiers which were pretty basic (just an H-bridge with drivers all mounted into one nice neat package)- those I understand. But I didn't know they had "linear" op-amplifiers that handled currents so high. Don't they dissipate tons of heat? Or do I need to brush up on my transistor knowledge?

I don't work with audio or anything like that- just robotics so I assume I would have run into these much sooner if I did. I guess they're just called "amplifiers" now instead of op-amps. I guess you would need them in things like really big speakers where you can't just switch on and off a transistor really fast...lol...Well I guess that's what a switching amplifier is isn't it? I guess there was a time when it was all analog and linear and not so much high frequency switching. I can't quite understand how a switching a signal on and off really fast can make something like DVD-quality sound though, but there's probably more to the system than that and some inductiveness going on to average out the voltage like in a motor, or some other mechanism. EDIT: Low-pass filter is the word I'm looking for.

But using an op-amp to drive a motor <-----blows my mind

I didn't know that switching amplifiers (well I didn't even know such things existed, or at least were considered amplifiers) were basically glorified H-bridges.

They don't seem to be cheap though. Well at least the ones from Apex are each $500+ even from the 150mA ones to the 50A op-amps or "linear amplifiers". Then again, the 150mA can run at 900V which is something you don't see in little IC op-amps. Still, expensive. The PWM amplifiers also cost the same. I could do the same thing for $20 with some transistors but it would probably only work for something like motors and not something where signal quality is needed like audio.

Hero999 · 28th December 2006, 12:29 PM

Quote:

Originally Posted by dknguyen

I also found switching amplifiers which were pretty basic (just an H-bridge with drivers all mounted into one nice neat package)- those I understand. But I didn't know they had "linear" op-amplifiers that handled currents so high. Don't they dissipate tons of heat? Or do I need to brush up on my transistor knowledge?

It's probably using class D amplification, nothing special.

**Nigel Goodwin** · 28th December 2006, 02:58 PM

You should bear in mind, most audio amplifiers are essentially just a high power discrete opamp!.

Analog · 28th December 2006, 03:10 PM

Philbrick corp made tube op-amps back in the 50s. Apex makes pretty high powered opamps today.

**Nigel Goodwin** · 28th December 2006, 03:20 PM

Quote:

Originally Posted by Analog

Philbrick corp made tube op-amps back in the 50s.

That's when opamps date from, they were used in analogue computers (which is where the name 'operational' comes from) - it's really only the development of cheap IC ones which made them a standard electronic component.

Hero999 · 28th December 2006, 05:16 PM

Quote:

Originally Posted by Nigel Goodwin

You should bear in mind, most audio amplifiers are essentially just a high power discrete opamp!.

Indeed, I don't see the point in buying a big op-amp when an audio amplifier IC connected to a small op-amp will do the trick.

**Nigel Goodwin** · 28th December 2006, 05:21 PM

Quote:

Originally Posted by Hero999

Indeed, I don't see the point in buying a big op-amp when an audio amplifier IC connected to a small op-amp will do the trick.

Except you already have!, your audio amplifier IC is a 'big opamp' - although often limited in some way.

ikalogic · 1st January 2007, 02:22 AM

so an op-amp like the lm386 could be used to drive mini motors?

dknguyen · 1st January 2007, 02:56 AM

I guess so!

**Nigel Goodwin** · 1st January 2007, 09:45 AM

It depends on the particular amplifier, often they don't give you all the connections you need externally - in particular the gain is often preset internally, with only minimal changes possible.

Hero999 · 1st January 2007, 11:55 AM

The gain would also be restricted to 20 because the capicitor that's normally used to boost the gain won't work at DC.

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28th December 2006, 07:43 AM	(permalink)
dknguyen	Humongous Op-Amps So it never occured to me that there existed ginormous op-amps that are capable of driving motors since all I have ever seen are the little IC things that amplify mA signals. I was looking at a link for a motor controller IC that someone asked about on the forum and their example circuit and it just had this measly little op-amp on the circuit driving what I assumed to be a motor. So I looked up this op-amp and it was huge! 10A! And then I looked into it more and found humongous 50A+ op-amps. I guess it never occured to me that people would scale up the op-amps I normally see to do these things. I also found switching amplifiers which were pretty basic (just an H-bridge with drivers all mounted into one nice neat package)- those I understand. But I didn't know they had "linear" op-amplifiers that handled currents so high. Don't they dissipate tons of heat? Or do I need to brush up on my transistor knowledge? I don't work with audio or anything like that- just robotics so I assume I would have run into these much sooner if I did. I guess they're just called "amplifiers" now instead of op-amps. I guess you would need them in things like really big speakers where you can't just switch on and off a transistor really fast...lol...Well I guess that's what a switching amplifier is isn't it? I guess there was a time when it was all analog and linear and not so much high frequency switching. I can't quite understand how a switching a signal on and off really fast can make something like DVD-quality sound though, but there's probably more to the system than that and some inductiveness going on to average out the voltage like in a motor, or some other mechanism. EDIT: Low-pass filter is the word I'm looking for. But using an op-amp to drive a motor <-----blows my mind I didn't know that switching amplifiers (well I didn't even know such things existed, or at least were considered amplifiers) were basically glorified H-bridges. They don't seem to be cheap though. Well at least the ones from Apex are each $500+ even from the 150mA ones to the 50A op-amps or "linear amplifiers". Then again, the 150mA can run at 900V which is something you don't see in little IC op-amps. Still, expensive. The PWM amplifiers also cost the same. I could do the same thing for $20 with some transistors but it would probably only work for something like motors and not something where signal quality is needed like audio. Last edited by dknguyen; 28th December 2006 at 07:57 AM.

28th December 2006, 02:58 PM	(permalink)
Nigel Goodwin	You should bear in mind, most audio amplifiers are essentially just a high power discrete opamp!. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

28th December 2006, 03:10 PM	(permalink)
Analog	Philbrick corp made tube op-amps back in the 50s. Apex makes pretty high powered opamps today. __________________ "Everything that is done in the world is done by hope." -Martin Luther "There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."-Albert Einstein

1st January 2007, 02:22 AM	(permalink)
ikalogic	so an op-amp like the lm386 could be used to drive mini motors? __________________ Ibrahim Kamal check my electronics and robotics page: http://www.ikalogic.com/

1st January 2007, 02:56 AM	(permalink)
dknguyen	I guess so!

1st January 2007, 09:45 AM	(permalink)
Nigel Goodwin	It depends on the particular amplifier, often they don't give you all the connections you need externally - in particular the gain is often preset internally, with only minimal changes possible. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

1st January 2007, 11:55 AM	(permalink)
Hero999	The gain would also be restricted to 20 because the capicitor that's normally used to boost the gain won't work at DC. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez