PWM for three 60w 120v bulbs (In a Traffic Light)

I built this interface using nothing but parts from a dead de-humidifier and two dead computer power supplies. Found the powersuplies in the garbage. ;). It’s been working great for about 48Hrs

Okay.. Um... how do I post the schematic?

stick it up somewhere eg. imageshack, photobucket, flickr etc

Then link to it.


You know, a bit smaller would be good :p

No auto-resize on here and I haven't got my multi monitor desktop set up yet ;D

OH dear lord it’s HUGE!
My humble apologies

OH dear lord it's HUGE! My humble apologies

Hehe no worries, good thing I have left/right scoll on this mouse as well as up/down.

Firefox zooms too :p

Let's see now.... and then maby

This deserves a pic :p

Mowcius ;D

Ya I deserved that.. nice screen rez BTW

nice screen rez BTW

The res was only 1280x1024 (shrunk to 1024x768 for the pic). I just zoomed it with firefox but when I get my quad screen setup sorted I will have: 4200x1400 ;D

So what do you think of the circuit? I realize the 20A 600V FET's are overkill.. but hey they were in the garbage and I have very limited resources down here in the trailerpark

Are you sure about that 14.5V transformer? Watch out that the peak voltage doesn't exceed the gate-to-source voltage rating of your MOSFET's. If it's 14.5Vrms NOMINAL from 120VAC NOMINAL then peak voltage is 20.5V, divided down by 91% gives 18.6V, let's say 18V after the optoisolator. That's a bit high for my taste. Maybe kick that 10k resistor down to 8.2k?

-- Check out our new shield:

It’s rated @ 30v±

You're right...that's one tough MOSFET.

-- Check out our new shield:

So what do you think of the circuit?

Looks like a good working circuit. However if you are going to be controlling it with a Arduino you can certainly simplify it a lot. If you convert to true LOGIC level mosfets (rated for the voltage/current required) you can eliminate all the opto-isolators and resistors and the low voltage power section. An Arduino output pin can directly drive a logic level mosfet gate terminal. Just be sure you add a wire from the high voltage minus terminal to a Arduino ground pin and you are good to go.