On Thu, 15 Aug 2002, Dave Tweed wrote: >Brendan Moran wrote: >> > I don't suppose you know of any 3volt three pin reset generators >> > that have an open collector output that can withstand the 13volts >> > Vpp on a PIC? Seems like no-one makes such a beast. >> >> I'd say don't worry about the open collector, and put a diode in >> series with the ouput. > >The reset generator still needs to withstand 13V if you don't want any >current to flow in the diode when the anode is at Vpp. It's unlikely that a >totem-pole device would meet this requirement with a 3V supply. One could use an inexpensive NJFET with the gate wired to +Vcc, D and S between the reset chip and the PIC MCLR pin. Raising S (MCLR) a few volts above Vcc will close the JFET so the 13V won't reach the regulator. The reg would see at most a few volts more than Vcc (Vcc + Vg0). A resistor in the gate is mandatory for when the MCLR is pulled low (probably 1meg or larger but not really critical). Any JFET would work here. It should accept -Vgs >= -10V imho. Buying these in bulk should not impact on the project cost imho. An inexpensive MOSFET could also work here and eliminate the resistor but beware the reverse bulk diode. I've also thought of using a single CMOS schmitt (TCxxx) gate as reset driver/brownout detector. I've also though of using its output to power the PIC directly for when the MCLR pin is taken. Not tried. Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads