----- Original Message ----- From: "Tony Goetz" To: Sent: Monday, August 13, 2001 6:12 PM Subject: Re: [EE]: MOSFET H-bridge > Russell Hedges wrote: > > << The on resistance of the IFR510, with a gate voltage of 10 volts, is > .54 ohms. What is the supply voltage? In any case, I think you want an > FET with lower on resistance. All FET's with lower on resistances. Low > RDS-ON is the parameter you need to worry about most. Higher current > FET's (with much lower rds-on) should source/sink more current through > your motor. And they are amazingly inexpensive. >> > > > The problem seems to have been in the transistors that turned the mosfets on > from the PIC. When connected exactly as the schematic shows (link at bottom) > the mosfets aparently wouldn't turn on all the way. The design uses one > transistor to turn on the P-channel mosfet, which would then turn on the > corresponding N-channel mosfet. Perhaps I didn't have enough power running > through the bridge to completely turn on both mosfets, but after hooking up a > transistor to each mosfet, it worked fine. Thanks for your input. > > http://www.cs.uwa.edu.au/~mafm/robot/blanch-h-bridge.html > > -Tony Glad to hear the boat is sea-worthy again =) I noticed you refer to transistors turning on the mosfets from the PIC. I've found it very helpful to use opto-isolators with appropriate biasing resistors to separate the PIC from the usually higher voltage H-Bridge and it's possible noise from the motors. Not sure if they are essential as I'm also a novice roboticist, but just thought I'd mention it as an alternative to the transistors. =) Cheers, Gygar -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body