Hello Peter,

> I want to switch 9 volts DC. I normally use a PNP and NPN transistor but I
> thought someone had a method using a single FET??

    if you're using a PIC and it's open-collector output is available, I
think you could use something like the circuit below. I have not done it
myself through.

                 9VDC
                 |
                 |
            +----+
            |    |
            /    |
        10KR\    |
            /    |
            \    D
    RA4-----+----G
                 S
                 |
                 |
                LOAD
                 |
                 |
               GROUND


     When  the PIC output is high (open, high impedance) the resistor will
maintain the Gate voltage at 9V and the FET will conduct. When the PIC
output is low (like a short-cirtuit to ground) the gate will be at ground
voltage and willn't conduct.

    Best regards,

    Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2685  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
www.citronics.com.br
-----------------------------------

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