On Fri, 12 May 2006, Edward Cooper wrote:

> I wondered if it was something like that, I'll look into swapping my diode 
> for a
> schottky I really want to keep this simple though.
>
> (Its a fan controller for a compact amp I've built and I'm aiming to get the 
> fan
> running at something near full speed at 1 v rms output - which is pretty 
> loud)

How about two transistors with less than 50mV 'switch on voltage' ?:

          +--+----- +5V for fan
          |  +--+
         R2 FAN C2
          |  +--+
          |  C
        E-+-B  Q2 NPN
IN-C1+B     E
     R1 C    |
      +-+----+----- GND
       Q1 PNP

For a sine wave input the voltage on C2 will be 1/2 Vcc so you can use 
12V to get 5V out.

Peter
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist