Many thanks! My plan was to have the photo-voltaic device continuously energized=20 and feed a decent-sized reservoir cap, then use a dual opto (discrete=20 NPN transistor outputs) configured as a totem-pole driver. One or=20 the other sides of the dual opto is always driven, depending upon=20 whether or not the load is energized or not. My original plan was to have the continuously-energized photo-voltaic=20 driver always feed the MOSFET gate, then use a single channel opto=20 short the gates to the sources whenever I wanted the load turned=20 OFF. No reservoir cap in this case. That is certainly the easiest. But I figured that for a few dollars=20 more, I could make it so that I can reliably turn the load OFF or ON=20 at any particular time with decent accuracy. I don't need much current rating - this device is a tester for=20 measuring the residual input voltage on devices with a=20 capacitive-style power supply. But it will also be used to measure=20 residual voltage on SM power supplies with significant EMI filtering=20 on the input. Thus the requirement for current capability of more=20 than a few hundred mA. The main requirement is that I have to turn the load OFF right at the=20 peak of the incoming AC waveform. So: can't use anything like a=20 triac or back-to-back SCRs. dwayne At 12:51 PM 6/14/2013, Denny Esterline wrote: >It's been a while since I did the design, but if memory serves, the bigger >difference between the TLP190 and TLP191 was the presence of an internal >pull down resistor on one of them. Thus one needs an external resistor and >the other does not. Fuzzy memory seems to suggest that the current >difference was naught once you added the external resistor. Bear in mind >that since the turn off time is controlled by that pull down resistor, >your're never going to get very fast switching with a PV opto. Plenty fast >for 60 Hz mains work, but you need to plan for a considerably longer time >in the linear region while switching. > >As to SSRs, not sure what you consider a "decent current rating", but a bi= t >of poking shows this candidate - good to 50A - >http://www.digikey.com/product-detail/en/D2450-10/CC1082-ND/221775 or this >one for 125A - >http://www.digikey.com/product-detail/en/H12WD48125-10/CC2007-ND/752475 >Though with your suggested loads >http://www.digikey.com/product-detail/en/S212S01F/425-2412-5-ND/720407 may >be a more suitable choice. > >Good luck >-Denny >-- >http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .