Power opamp.. output "near" the rails.

Hi all, browsing power opamps at DK. I need something with at least 300mA of output current at least +/- 5V power supplies, and with an output that will get within a volt of the rails. I've used the rail-rail opa569, but not enough voltage. The OPA561 looks like it would work... "not recommended for new designs".

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replaced with the opa564,
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Which at the moment looks like the only "winner".

Anything else I might look at?

George H. (Apex parts need not apply.)

(the LT1970 might work... separate output supply pins, but I couldn't find the spec for the voltage drop on the output... it's also LT-spendy.)

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Reply to
George Herold
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You might parallel a bunch of these

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It's a cheap little rail-to-rail amplifier, but the output stage can deliver quite a lot of current - 80mA. Put a quad package's worth - MC33204 - in parallel and you might get your 300mA.

The quad costs a a couple of dollars in small quantities, and Farnell/Newark seem to have plenty. Joerg wouldn't like it, but your customers have deeper pockets.

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Bill Sloman, Sydney
Reply to
bill.sloman

What about this bad boy right here?

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Or bootstrap the supply rails? Or both?

Reply to
bitrex

Hmm OK thanks Bill, the power opamps I'm looking at are ~$5 so price is OK. It will have to dissipate ~1 Watt (worse case) (I forgot to share that spec.) I was looking for something with a thermal power pad or similar.

George H.

Reply to
George Herold

I've got that bad boy in my parts box... never used. It might have to dissipate 1W.. which makes me a little nervous.

I'm not sure what you mean by boot strapping the supply rails?

George H.

Reply to
George Herold

TCA0372, dual 1 amp, 45 cents.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

Golly Mr. Wizard, good suggestion!

Reply to
bitrex

By Apex, are you referring to a specific trade mark or something else?

What is your frequency response requirement ?

Some amplifier for low voltages use voltage amplifier output stages (not emitter followers) so you get close to rail to rail.

An car audio amp would work with at least +/- 7 V and would deliver sufficient currents for your requirements.

Reply to
upsidedown

We've used them in several products, and they seem well behaved. Not c-load stable, but you can work around that.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Oh sorry, Apex makes HV and power opamps. They were part of my digikey search. I had some bad luck with one of their HV opamps and I've scratched them off my list... well unless I need them again in the future :^) They are spendy too.

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Yeah frequency is modest, DC to 10k Hz. Actually this thread should be stopped. I made a mistake in my power calculation and the I can run this off 15 volts rails with lots of head room, ~2W of dissipation. and a power opamp in stock (opa544). (I multiplied 0.2 by 10 and got 5... go figure.)

George H.

Reply to
George Herold

This is driving a coil. What sort of power dissipation?

George H.

Reply to
George Herold

Driving coils dynamically can get nasty, because it can put an opamp into a high-dissipation quadrant. Better Spice it.

Here's a TCA0372 acting as a programmable power supply with loat of capacitance in the loads. The real thing will use DACs instead of pots.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Hmm... this is fairly low frequency (DC - 10 kHz.) I'm not even sure of the coil parameter, R = 10 ohms, air coil. Can I guesstimate a problem frequency as when I get above the L/R time?

It's someone else's design, I was laying out the circuit and thinking about worse case power dissipation. (which I screwed up.)

George H.

Reply to
George Herold

So use a handful of single or dual parts. One watt spread across several packages isn't going to be a problem.

One watt at 300mA is a 3.3V drop. A resistive load to ground from +/-5V supplies would give a peak dissipation in the op amp at +/-2.5V times 150mA which is 0.375W.

You spec did need more detail.

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Bill Sloman, Sydney
Reply to
bill.sloman

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