fan speed control with temperature

[pankajwillkillu]

OK , directly expressing the problem scenario .
I have a temperature sensor [IC LM 35], comparator [IV 741 opamp] , a fan [18V D.C fan], thyristor [SCR TYN612M].

Now, i want to use them over to form a circuit capable of controlling my fan speed in proportional to temperature.
Is there a way out to form a simple but effective circuit out of this?
HELP !



i know what to do but don't know how to do (eg, i don't know what values of L-C pair should i employ for simple commutation of SCR)

 

[pankajwillkillu]

transistor

SCR needs to be ruled out of scene i am thinking of using BJT transistor with enough rating to start working with LM35 output being fed to its base.
Will it work?

If yes, then what rating of transistor should i choose and are there any other pheriferals(resistors,capacitors etc) required