I need a circuit that uses 0-14.5 Vdc to control a valve that is 20W (at 12Vdc). I purchased a 0-5K ohm electric bike handle grip. The grip looks like it can only handle 0.5 Watts. I have tried to use a 2SC4793 NPN transistor with a voltage divider to control the base. I am not having any luck with this. The transistor will only output 0-6 Volts. I used one transistor to power a second transistor but that didn't work very well either. Has anyone seen any circuits like this, or could you point me in a better direction?

Thank you.

 

Can you post up the schematic of your circuit? We can make much better guesses with that in hand.

 

Try it like this:

You'll likely need a heat sink on Q1.

 

I think a valve can only be switched on and off (not something intermediate), does it?

 

Mik3, I think you're on to something.

At least if it's a pressure regulator valve. A chopper circuit would be much more appropriate - and much more efficient - along with being much more complex.

 

ZipperJeremy give more information about the valve or its datasheet.