At 10:44 PM 1/24/2006, Rob Robson wrote: >I have an LM1972 uPOT on +/-5V rails feeding a TL072 on +/-12V rails >wired as a unity gain buffer as per the LM1972 datasheet. I've used >this circuit for years with a linear power supply without any >problems, but when the circuit was ported to a system with a >(noisier) switching power supply, the TL072 would latch up after >only a few hours of operation . First problem: I had put the TL072 >on +/-5V rails without consulting its spec sheet (too low, as it >turns out), so I substituted the more forgiving LF353. The latch-up >condition would still occur after several hours of operation. Which latch-up condition do you refer to? There are two: SCR type latch-up where the chip draws significant current *or* phase-inversion latch-up where the output of an op-amp swings hard to one rail because one or both inputs went out of the common-mode voltage range. I'm assuming a phase-inversion type latch-up but it would be useful to have that confirmed. Like Bob, I've been using the TL07x family for a couple of decades, in at least a hundred different products (probably way more than 100) without incident. The TL07x family does include the positive supply rail within the common-mode voltage range. Can you try adding an external negative supply such that the negative rail is at least 3V lower than the lowest expected signal? I'd suggest starting off at -8V or -9V. Leave the + supply rail at 5V. Then let the thing run and see if the problem occurs. Are the TL072 inputs exposed directly to the outside world? What signal range are you expecting? dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 21 years of Engineering Innovation (1984 - 2005) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist