PWM with timer on a 12v constant voltage power supply?

I have 5 - 12v LEDs running in parallel. Each lamp has it's own heat sink, fan and resistor,. Each one steadily uses about 850ma. I'm hoping to add a timer of sorts, something that adjusts the light level on a schedule. I've read about people using something like a 555 and/or the Arduino, but I'm kinda lost. Any pointers?

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Use a MOSFET driven by the arduino pin, or by a simple 555 timer.

You'll probably have to connect the fans to the supply directly though, because they aren't going to like running on PWM at low duty cycles.
lford4 (author)  steveastrouk5 years ago
How do I go about picking out the correct one? To save myself some trouble with the arduino sketch I'm hoping to only use one for this project at first. But I would like to know how to pick them out so that I can apply it again on the next project, which will probably be adding the MOSFET to each of the LED's for better control.

Should the source-drain be exactly 12v - 4.250 amps?

How about figuring out what the gate should be rated. Some of these are showing 20v, and don't mention anything about the pulse.
Don't worry to much about any other part of the rating but Vgs sat, and Rds on.

The MOSFET is purely a switch here. It needs to be turned on hard, so its Rds is as low as possible. Since you only have a logic pin to drive it, you really need a "logic level MOSFET", Like an IRL 540 - The IRL indicates its a low voltage gate.

So long as the Vds max > 12V, and the maximum Drain current is >5 x 0.85 A, you're good to go.

lford4 (author) 5 years ago
Perhaps use the Arduino to signal a NPN transistor that's able to handle the amps?