LM358 RRO

I don't know this opamp. Like the LM324 we've been discussing?

Does rail to rail out mean ~ 1 saturated transistor (Vce) drop?

I'm afraid I don't 'get' the circuit. You're loading the opamp with ~1.5 mA current source. This keeps the pnp output transistor to the neg power rail always on. Is the power opamp a buffer? Isn't the rail to rail performance limited by the power opamp?

George H.

The LM358 specs look identical to an amp in a LM324N. The LM358A has somewhat better Voffset and input bias current tolerances.

It's basically a dual version of the 324.

I'd like it to go within millivolts of the positive rail. "RRO" usually means all the way.

The power amp is a TCA0372 as a follower, which will pull up to within

Since my load on the 358 is an opamp, I guess the depletion fet could be replaced with a pullup resistor. The opposite of what people usually do to an LM324.

I can't add gain to the big amp, which would solve the swing problem, because it messes up my clamp thing.

TCA0372 is amazing. A dual 1-amp opamp for 47 cents. The LM358 costs

Hmm, well a resistor voltage divider here and one on the opamp. If it's just a diode clamp, those (for me) have mussy corners and temp. dependence anyway.

I had some TCA0372's I started to use 'em for a few projects and then didn't like something and used a spendier opamp. This would have been audio AC stuff.

George H.

I want to protect my GaN fets from being reverse biased very much. They don't exactly have substrate diodes but could be damaged by reverse voltage drain to source.

Doesn't look as though the current sink on the output stage is enough to overcome the LND250's 1.6 mA, so I sort of doubt it'll pull below V_EE +

Cheers

Phil Hobbs

Regards, Clemens

I really want it to swing to the positive rail.

I guess I could add yet another opamp to stock. I'd want RRIO, dual,

My fave, OPA197, is a single SOT23 for 68 cents by the reel.

OPA2171, about 90 cents in thousands.

OPA2140. 40V single supply, RRO, 5 nV noise, 20-Hz 1/f corner (amazing for a JFET amp), 120 uV VOSmax, 1uV/K TCmax, 10 MHz, 20V/us. $3 in thousands. (Otherwise it stinks.)

OPA2141, worse input accuracy, otherwise very similar. $1.50 in thousands. Not a bad deal at all.

Cheers

Phil Hobbs

opa2197?

OPA192 is useful for current measurement off the positive rail- 36V, low Vos, RRIO. Worth stocking, IMHO.

A bit pricey though, ~1.20 USD in 1K.

Best regards, Spehro Pefhany

A pretty nice part though--40V RRIO JFET, with offset trims done after packaging. Weirdly the N-channel input stage is ~10 dB noisier than the P-channel one. Discrete N-cnannel parts are way quieter than P-channel ones.

Cheers

Phil Hobbs