4quad supply

It is a great part, except that its theta-JC is ridiculously large. (I expect they crippled it on purpose to restrict it to audio because it's so cheap.)

On +-15V supplies, it runs noticeably warm with no load, because its quiescent bias current is 8 mA typ, iirc. If they'd put it in a D2PAK or something, it would be a beast. I've used it for things like rail splitting, but only when the main load goes across the real rails.

I'd be nervous about subjecting it to the outside corners of quadrants 2 and 4 for very long at the levels you're talking about--it would be liable to toast itself.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

It really needs a power pad. Too many pins for a dpak.

I think I'll be OK. I'll heat sink the four Vee pins, and put a good ground pour under the body. So if I need to, I can put something thermally conductive under the chip, some Bergquist gap-pad stuff maybe. I already need to blow some air on this part of the board.

I could glue a heat sink to the top if things got grim, but I expect it won't come to that.

A few opamps admit to being c-load stable. A few more are good without it being advertised. Most aren't. It's hard to predict. Even if people give us an equivalent schematic, it's not always true.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Hmmm. 10*C/W. (DIP-16)

OnSemi seems to push it as general-purpose--

"The TCA0372 is a monolithic circuit intended for use as a power op-amp in a wide range of applications, including servo amplifiers and power supplies. No deadband crossover distortion provides better performance for driving coils."

One wonders if OnSemi's package 966 version (SO-16) has better thermal performance, but their spec sheet doesn't give thermal data for that package.

It *is* a nice-looking part.

Cheers, James Arthur

It seems to be well behaved.

I'm using the wide SO16, which is rated 12 j-c and 80 j-a. I might dissipate a watt worst-case, maybe a little less, so I should make some modest effort to get the heat out.

Mount a tiny tea kettle on top?

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Hmm. With +-15V supplies, sinking 100 mA from +12 is 2.7 W. Per section. (Tweet! Goal posts in motion. Five yards, second down.) ;)

They could make a single that would go in a D2PAK or TO220--it would only need 4 pins plus the pad.

The power handling is in the LM317 class, which makes the packaging ridiculous. 30V, 1.4A, SO-16. Weird.

Cheers

Phil Hobbs

Huh... I've got that part in my drawers* but I've never applied power. (I keep waiting for the right project... more than 30 mA, less than 300 mA.) But I was going to ask if anyone had tried it for driving coils. (which is my typical high current app.)

Oh I've got another question too. I've used the classic circuit for slowing down the opamp for driving a big capacitance... (shown in JL first picture above.) Is there something equivalent when driving a coil? (All I've every done is a Zobel thing across the coil.)

George H.

Hope it's not the DIP. Yeeouch! ;)

Audio is one big application, so it ought to be okay driving a speaker, at least.

Since the coil's impedance ought to be largish up near the unity gain cross, I wouldn't think it would be a big issue. Anyway, unless the coil's self-resonant frequency is low, the phase will be leading, which won't hurt stability.

(I haven't built a coil driver since my audio projects as a teenager.)

Cheers

Phil Hobbs

I don't expect to hit total chip dissipation above one watt. It's complicated.

It does thermal limit, so mounting/heatsinking experiments can be done. The board that I'm laying out now is a little test tile, and I can futz with that before we attempt the real thing... if the other parts work.

I'm making a pulse generator output stage, and the opamp supplies programmable Vhi and Vlo. That's the easy part.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

It would almost need a constantly emitting can of cold spray.

Except with capacitive loads. When I have to drive capacitive loads I like class D amps.

Or the wort pot, for the next batch of IPA. Can't wait to get started.

--
Regards, Joerg 

http://www.analogconsultants.com/

I'm driving a capacitive load, but he voltage doesn't change between manual settings. I don't *want* the voltage to change

It seems to thermal limit OK, so there would be no damage. Worst case, I can change the specs to say "Don't Do That!"

Tiny beers?

I can't drink IPA, and that's 90% of the boutique beers these days. It's a hops arms race, competition to see who can make the most bitter beer. That must be easy to brew: use enough hops and nobody can taste anything else.

Grrrrr.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

But I assume you want it to regulate out load changes which is where opamps can develop serious attitude issues.

IME stuff that hits the thermal protection peg all the time does not have a long average life expectancy.

It looks like the maker scene has produced some fruits in that direction:

Yes, it sure is. I wish there were more classics such as Pilsener and clean (meaning non-sweet) bock beer. One of my bicycle watering holes often has Koelsch Style which you'd probably like. Brewed right there. When they do I bring home a growler.

Tonight will be the first time I'll bring home a growler via a long gnarly mountain bike trail which is the only bike connection to Placerville. Wish me luck. I sure hope it won't explode on me in the pannier because that is right behind my left leg.

I like hoppy taste. My current favorite is a beer they seem to only serve at their pub and it's not on the list, called "Reckless Use of Hops". 10.2 volts, by these guys:

--
Regards, Joerg 

http://www.analogconsultants.com/

I don't know of any 4-quadrant voltage regulators that would do what I want. Maybe one of the rail splitter things? That TCA0372 opamp is pretty good, with a little help: dual, cheap, swings close to the rails.

LT1010 is OK, but old and expensive and has enough offset and Zout that I'd have to close a loop around it, too. I need an opamp somewhere anyhow, since my DACs won't swing 20 volts.

Free engineering is welcome.

Lawnmower beer? That sounds disrespectful.

Well, OK. I put five or six packets of sugar in my coffee.

Some of the Japanese beers are good, like the Asahi super-dry stuff. Comes in giant bottles.

The new Guinness Blonde is good. Harp is nice.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Ah, so not very four-quadrant, not like a Kepco BOP, say.

The last time I used a TCA0372 was to move the tip bias voltage of the TIA in the Qcept zillion gigohm front end.

The simplest way to get stable performance was to move the power supplies and the local ground, so I had a couple of three-terminal regulators referenced to the output of the TCA0372, and a instrumentation amp to get rid of the offset afterwards.

Fun.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

FYI, you want the R1+C1 feedback network (i.e. a "type 2 compensator") equal in time constant to the series R2 and C2 load. So, R1C2 = R2C2. Give or take.

Tricky when C2 varies (variable length cables? general piezo driver?), in which case you need to pick the worst case and just settle for crappy ramps on light loads. Meh, it's better for EMI that way I suppose.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

Four quadrants, but not all are the same size!

Right. The dropout voltage of that amp is pretty low, so one could bootstrap the supplies to the input or, for the brave, to the output. That moves most of the heat into the regulators. I could do that if I get into trouble.

Sometimes bootstrapping to the outputs has interesting side effects. Did yours work OK?

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

It doesn't have to be an ideal crossover; mine sure isn't. I just grabbed some handy parts. I guess transient-load regulation is optimized when the time constants are close.

I don't know the open-loop output impedance of that opamp, so breadboarding is as good as trying to do the math.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Have you looked at this one?

--

John Devereux

Worked great. The output impedance of the TCA0372 is super low, so the regs didn't even notice. Of course the op amp was running off fixed supplies--it was just the +-5 TIA supply that moved. (BF862s are nice and happy with 2V D-S. That keeps down the drift and avoids impact ionization gate current.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Huh! I'm brewing a Honey Blonde ale as we speak.

I had a Track 7 Beeline Honey Blonde months ago and fell in love with the taste. The cans just don't taste the same as on-tap though.

They even posted some of their specs, so I tried to make my own.

Munich and Vienna malts. Fuggles, Magnum, Tetnang hops.

Fermenting with honey is weirder than your regular fermentation... takes about twice as long, and foams all over the place (I've been cleaning the airlocks daily.)

Will let it sit for a week before the cold crash :)

Michael