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Issue with constant current source for LED

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Aluz:
I've been trying to build a constant current led control circuit, but I'm not sure why it's not working. I'm using the arduino output to control I_SP. Output voltage for LED is extremely low for some reason. Should be around 7-8v but for 12v supply is around 2-3v.

Any help would be much appreciated.

PCB.Wiz:
It's more common to put the LED in the FET Drain, as that gives lowest voltage loss.
As you have it now, the VGS of the fet subtracts from the VCC range.
Moving the LED eliminates that Vgs dependance.

Aluz:
Oh I see, should the wire between R3 and Imeasure exist?

PCB.Wiz:

--- Quote from: Aluz on June 08, 2023, 12:08:07 am ---Oh I see, should the wire between R3 and Imeasure exist?

--- End quote ---

Yes, that's needed for feedback.
You move the UV LED up on the SCH to connect the + to VCC and - to MOSFET Drain

magic:
Measure voltages at all inputs and output of U1 and Q1 and see what isn't behaving the way it should.

If you have a scope, check if there is no oscillation.

Not sure what's the point of R3? Maybe you copied this schematic from somewhere and R3 was meant to go to U1 IN- rather than VCC?

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