Using a FET as a relay

[imagineerdan]

Hi, I have been playing with FETs like the IRF540 and was wondering how I would hook it up as a relay. I want to PWM it from the stamp so I can drive a larger current set of Luxeons. I am having trouble with the gate, drain, source and such. How would it be wired? Thanks!

Dan

[JonnyMac]

I've not used this circuit myself, but it does come from a reliable source: Al Williams (a friend, but we're not related).

[imagineerdan]

Ok that works greatwith PWMing an LED which uses an off board power source, BUT I am finding now the ULN is getting very hot, what do you think is causing this?

[JonnyMac]

The only reason the ULN will get hot is that you're running too much current though it.  The circuit above should be connected to a TTL output pin, not a ULN output (terminal block).