I have a situation where I'd like to operate an op amp as an integrator, to use in a feedback loop as a DC servo for a certain node in a circuit. The node will be at a relatively high potential (~150 volts), so I'd like to use a regular op amp with its positive and negative supplies tied to say, 160 and 140 volts respectively.
Any potential (heh) gotchas to be aware of in such a configuration?
Startup and ESD, I suppose. Voltage is difference, the amp only knows what it can can see.
Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website:
"bitrex"
** Plenty.If inputs are driven beyond the supply rail voltages or the supply voltages go outside their nominal levels for ANY reason - the op-amp will suffer damage.
Suggest you use a hefty zener to clamp the + & - rails and put reverse biased diodes from each input to each rail too.
Diodes protecting the output may be a good idea also.
Lotsa diodes.
... Phil
That sort of use requires some very careful considerations. Three-way Isolated Amplifiers have galvancially isolated supply, input and output and would be the type of device I use in this situation. There are some good ones on the market but as you haven't stated the input voltage or current levels or what sort of output you would expect it is hard to be specific about this.
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Startup as well as _shutdown_ can cause problems.
Another outdated and completely unoriginal suggestion from the pompous windbag...
Just make sure that none of the inputs can get slammed past the opamp rails.
We do this a lot, in out MRI gradient amplifiers, floating opamps on power rails a couple hundred volts off ground. The opamps are driven by floating bipolar power supplies or, if single-supply, by a zener from the big HV rail towards ground. If you need to bring in a control signal from ground, a controlled current sink will work.
Probing is tricky. Of you intend to do this a lot, get an isolated-input scope, like a TPS2024. Those are great to have around anyhow.
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I concur on the choice of scope for any probing around the circuitry. Good isolation between channels and to ground. Really handy in High Power Motor and Solenoid Drives also.
-- ******************************************************************** Paul E. Bennett IEng MIET..... Forth based HIDECS Consultancy............. Mob: +44 (0)7811-639972 Tel: +44 (0)1235-510979 Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. ********************************************************************
Is there any reason a HV transistor won't work? Inverting voltage gain is all you require of an integrator, the fully-differential sensitive inputs of an op amp are .. not required. Program a suitable emitter current with a big resistor, and you're good to go! For extra gain, a darlington is nice...
Fuck off ASSHOLE or this NG will be sabotaged.
... Phil
That may be an option. I'll look at the circuit again and see if it's possible.
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