At 05:04 PM 1/28/03 +1300, Jinx wrote: >The 12V sealed lead battery in a piece of equipment has been >left connected to a circuit long after after the mains charging was >switched off. It's got almost 0V across it and is poked. I'd like to >add a low battery switch so this doesn't happen again. > >Example via Google How much current? That example seems like serious overkill for the kind of current consumption that most portable equipment would consume. How about a P-channel MOSFET combined with an open-drain low voltage reset controller? I'm thinking of the modern equivalent of the old Intersil 7211 / 7212 battery monitor chips. I know Microchip, Motorola, Seiko, Maxim all make these - available in 3 legged TO-92 packages as well as SMT. So long as the open drain output can handle the voltage of the gell cell at end of life voltage, it should be OK. I see a circuit consisting of the MOSFET, the reset controller, 2 resistors to set the threshold on the controller and a G-S resistor on the MOSFET to ensure that it turns off when the reset controller goes to the open drain condition. I just had a look at the Microchip offerings - none of those seem suitable since they spec that the open drain lead is constrained to within the range of Vss to Vdd. But I'm sure that I've seen others that allow the open drain lead to go to +18V or so - I just can't put my finger on the part number right now. Anyways - just one idea. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' 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 hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics