> Date: Wed, 27 Oct 1999 17:13:07 -0400 > Reply-to: pic microcontroller discussion list > From: Andy Kunz > To: PICLIST@MITVMA.MIT.EDU > > > > > > It is all connected as follows: > > gate porta-0 source 5v drain to motor Am i being a complete tit ? > > Not a complete one > > You should have the FET between the motor and ground. This is called a > "low-side" operation. > Im afraid Andy is a bit on the wrong side here... The IRF 9530 is a P channel device as Aaron stated but it is not a logic level device, so even though the connections are correct there is insufficient drive voltage to 'enhance' the channel(turn it fully on). Most non logic level mosfets turn on fully around 11 volts. So a P channel mosfet will turn on fully when the gate is 11 volts LOWER than the source. So +5V source will need a -6 volt gate drive, sad but thats Physics. The problem can be fixed by a logic level Mosfet as I stated in an earlier posting BUT beware a Pchannel Logic Level Mosfet will switch properly with a +5 volt (some will be on at 3 volts) source BUT if you up the source to 12 volts the mosfet will switch fully on at +5 volt as this is 7 volts lower at the gate than source so your 0 to 5 volt drive will result in the mosfet on in all circumstances. Just a trap for newbies... one of my first mistakes.. thats why I prefer N channel, apart from being cheaper. _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand www.psych.auckland.ac.nz _____________________________