Lowering excessive amp supply voltage using diodes?

Question

I need a rail to rail amp to replace the INA amp here: Multiple ground

After a short search I only found RRIO amps whose supply voltage go to max 5.5 V.

Now my supply is +-2.85 V, would it be correct to lower the supply for the op-amp with a diode?

Is a Schottky diode's voltage drop about 0.3 V?

Would it be OK or there is a better way?

could you link to a datasheet of the amplifier IC you're referring to? It's not clear to me which you mean. — Marcus Müller, Nov 10 '21 at 15:14
None in particular. I have seen 6/7 RRIO op-amps from different manufacturer that go as high as 5.5v max — Status Re, Nov 10 '21 at 15:27
um, so then your question is simply based on the assumption that no RRIO opamps work with supplies exceeding 5.5 V. That assumption is wrong. — Marcus Müller, Nov 10 '21 at 15:35
I’m voting to close this question because it's based on a wrong assumption. — Marcus Müller, Nov 10 '21 at 15:35
Not so fast please. I said that i couldn't find one. So the real question is if I can lower my supply with diode's (you see, where the question marks are) — Status Re, Nov 10 '21 at 15:40
re your last question: the better solution would almost certainly be just using a opamp with an appropriate supply voltage range. — Marcus Müller, Nov 10 '21 at 15:43
Just to give an example, Texas Instruments currently lists 92 RRIO op amps that will take 6V and more. — DamienD, Nov 11 '21 at 13:15

score 3 · Answer 1 · answered Nov 10 '21 at 15:49

You can add some LDO regulators eg. +/-2.5V.

Diodes have relatively high impedance and you might have other issues as a result of trying to use them. If you throw away power by adding bias resistors and bypass capacitors it might be usable but you'd have to carefully evaluate the effects of the dynamic supply voltage variations and PSRR on the output accuracy and distortion. Simulation may not adequately model such effects.

However, I agree with @MarcusMüller 100%, just do a longer search so as to find and use an in-amp that is happy with the higher voltage.

yep, that's certainly a way to go. Checked: +-2.5V LDOs are back in stock at farnell, so the world's turning slowly normal again. — Marcus Müller, Nov 10 '21 at 15:54

score 2 · Answer 2 · answered Nov 10 '21 at 15:46

Is a Schottky diode's voltage drop about 0.3V?

Can't be said in general: your diode only has a voltage drop if there's current flowing through it, and what current leads to which drop depends on the diode!

Now my supply is +-2.85V, would it be correct to lower the supply for the op-amp with a diode?

So, until current starts flowing, the opamp will be exposed to overvoltage, which might or might not cause an excessive current flow through some internal circuitry.

So, you'd need

a specific diode's datasheet with which you can deduce the voltage drop given a current,
an opamp datasheet that at least suggests how much current can be safely injected in an overvoltage situation.

Would it be OK or there is a better way?

Simply use any of the many opamps that have a larger supply voltage range.

Thank you all. I'll do a Better longer search – Status Re Nov 10 '21 at 16:00 — Status Re, Nov 10 '21 at 16:00

Lowering excessive amp supply voltage using diodes?

2 Answers2