static precaution, fet opamp

such as TL062 (but could be anything low current). This thing is going to be used in uncontrolled conditions in the 3rd world, and needs to be relati vely reliable.

xtra static protection do I need. What I've added so far is a diode from 0v to the outwide world input, and another diode from opamp -in to the half V cc rail, which has 0.5M resistance and 0.22uF smoothing cap. (Its very high impedance for a reason.) The 2nd diode goes to half Vcc not Vcc since its smoothed, I don't want the diode capacitance coupling psu crap to the opamp input.

d them doing too. I'm thinking 2 diodes + resistor on the output. Power inp ut is protected by a reverse diode plus a very small reservoir cap.

Just to clarify I basically am looking for the minimum configuration that'l l do the job. Otherwise I'd stick diodes & resistors all over it and not wo rry. Thank you.

NT

p, such as TL062 (but could be anything low current). This thing is going t o be used in uncontrolled conditions in the 3rd world, and needs to be rela tively reliable.

extra static protection do I need. What I've added so far is a diode from

eed them doing too. I'm thinking 2 diodes + resistor on the output. Power i nput is protected by a reverse diode plus a very small reservoir cap.

'll do the job. Otherwise I'd stick diodes & resistors all over it and not worry. Thank you.

There isn't really any effective short cut is there. :)

NT

What voltage range?

What supply range?

What devices are available (clamp diodes, zeners, TVS, galena crystals and other floor sweepings...?!)?

How much capacitance/resistance load is permissible? What bandwidth? Distortion specs?

Also, presumably you have a feedback resistor to -in somewhere, or at least a bias resistor to ground. Otherwise that input's flapping in the breeze and will eventually saturate one way or another...

Tim

-- Seven Transistor Labs Electrical Engineering Consultation Website:

The outside world goes to -in via 68k + 47nF. Question is what level of extra static protection do I need. What I've added so far is a diode from 0v to the outwide world input, and another diode from opamp -in to the half Vcc rail, which has 0.5M resistance and 0.22uF smoothing cap. (Its very high impedance for a reason.) The 2nd diode goes to half Vcc not Vcc since its smoothed, I don't want the diode capacitance coupling psu crap to the opamp input.

The opamp has no static protection on other pins yet, I daresay it'll need them doing too. I'm thinking 2 diodes + resistor on the output. Power input is protected by a reverse diode plus a very small reservoir cap.

Enough? Overkill? Completely wrong?

NT

The TL062 is a jFET input op amp; it's unlikely to take harm from the small charge of a static jolt, because it doesn't have a thin oxide that can be punctured. There's plenty of protection diodes, accidentally built in. Thermal overload can happen, though; you can protect it with a fuse or fusible resistor against that, or use back-to-back zeners. If you use protection diodes, and 220VAC is applied, there might be over half a watt dissipated in the 68k resistor; can it take that?

the least possible cost devices from scrap electronics. I'm going so far with unspecced small diodes plus resistor.

its driving around 1mA load. I don't want to increase that current by much. Power consumption is the big deal on this one.

audio

'meh' is the official distortion spec

sure, I'm not worried about it saturating though.

NT

I presume one can't count on either of those with random opamps.

I can't see that being a problem in this circuit.

It doesn't need to survive 220v. If it were applied, its a gamble as to whether the input cap would take it. 47nF so likely ceramic, so the odds aren't bad. If it did, everything else would hold up ok.

NT

amp, such as TL062 (but could be anything low current). This thing is going to be used in uncontrolled conditions in the 3rd world, and needs to be re latively reliable.

of extra static protection do I need. What I've added so far is a diode fro m 0v to the outwide world input, and another diode from opamp -in to the ha lf Vcc rail, which has 0.5M resistance and 0.22uF smoothing cap. (Its very high impedance for a reason.) The 2nd diode goes to half Vcc not Vcc since its smoothed, I don't want the diode capacitance coupling psu crap to the o pamp input.

need them doing too. I'm thinking 2 diodes + resistor on the output. Power input is protected by a reverse diode plus a very small reservoir cap.

at'll do the job. Otherwise I'd stick diodes & resistors all over it and no t worry. Thank you.

ok, on the output I've got 390R then diodes to 0v and Vcc. I think the answ er to the next question is no: can I rely on those diodes to also protect a gainst wrong battery polarity? They'd limit Vcc to about -2v.

NT