This Circuit was Designed by me in 2002 to control the
12 Volt, 5 Amp Fan on the propane furnace in my truck.
It saves killing the battery when the truck is not running.
It works VERY NICELY and also acts as an On/Off switch.
For best Stabiliy, it is recommended that these units be connected
"directly to the car battery".
If you don't, it can trip because of voltage drops in your cars electrical
wiring, Especially as you turn things on.
The "First Schematic" shows a Mosfet Driving a "Load" by grounding
it to the negative of the supply.
In this Situation, the Mosfet SINKS the Negative of the load to Ground.
Alternately, The "Second Schematic", created Mar 2008 uses a
P-Mosfet to supply power to loads that are presently grounded.
NOTE: The 47K resistor may need to be adjusted in value to
give you the appropriate range of control you require.
** This is due to Variation in these IC's.
The 5 Volt Regulator on the Circuit Boards is to Stablize the IC Supply,
Resulting in a stable trip point of the IC.
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