Rob Robson wrote: >Thanks very much for the suggestions. The load impedance change was caused >by a change in resistor values around the 5532 summing amp that follows the >latching-up LF353. I've now reduced those values by a factor of 10 and I'm >retesting. It took about 22 hours for the fault to appear each time, so >it's too early to tell whether this change will fix it. > >In researching this problem, I came across an article that claims that the >TL072 is particularly susceptible to latch-up, although I've used them for >years without problem. I'll provide the link if I can find it again. > > I'd like to see it. Wow, TL072 is in hundreds of designs, never a failure. >This is a 2-layer board with an external switcher, but the bottom layer is >virtually all ground. Should that suffice? > > That should be enough. >What would be the simplest way to protect the op amp input from spikes? >Zener to ground? > > Try current-limiting with resistors, if you can, if it won't screw up the design. 100 ohms might do the trick. Zeners are no good for transient suppression. Use Transorbers or other TVS types. The good news is that there are TVS in 0603 packages, and they work great! --Bob >Thanks again, >RR > >----- Original Message ----- >From: "Gerhard Fiedler" >To: >Sent: Wednesday, January 25, 2006 3:46 AM >Subject: Re: [EE]: op amp latch-up problem > > > > >>Rob Robson wrote: >> >> >> >>>Besides power supply noise, the only other difference betwee n the >>>functioning legacy circuit and the faulty new one is the impedance >>>they're each looking into: 2.7k for the former; 22k for the latter. Does >>>anyone have any ideas about what might be causing the op amp to latch >>>up? >>> >>> >>Not really. But possibly you're one step further if you check whether your >>circuit works with a 3k resistor from the output(s) to ground (so simulate >>the earlier impedance). >> >>What did you change to cause the impedance change? >> >>Gerhard >> >>-- >>http://www.piclist.com PIC/SX FAQ & list archive >>View/change your membership options at >>http://mailman.mit.edu/mailman/listinfo/piclist >> >> >> > > > > -- Note: To protect our network, attachments must be sent to attach@engineer.cotse.net . 1-520-850-1673 USA/Canada http://beam.to/azengineer -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist