I think this will work.
One charm of the old parts is that the data sheet includes a transistor-level schematic.
-- John Larkin Highland Technology, Inc The cork popped merrily, and Lord Peter rose to his feet.
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
1 volt of my +24 positive rail. I just don't want to give up any more swing in the driver amp.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
10 cents.-- John Larkin Highland Technology, Inc picosecond timing precision measurement
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.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement
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 +
0.6 V. Should go to the positive rail, though.Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
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,
32 volt supply. That's rare. OPA2990 is a candidate, 48 cents at 1K.My fave, OPA197, is a single SOT23 for 68 cents by the reel.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement
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
-- Dr Philip C D Hobbs Principal Consultant
opa2197?
197/2197/4197, single/dual/quad
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
-- Dr Philip C D Hobbs Principal Consultant
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