# Help to make an uA opto dimmer?

#### FriedMule

Hi I am run into a kind of wall! How do you make a current dimmer?
I want to dim an opto coupler via a single turn pot.

Coupler Spec is 1.2V-1.4V @ 0.1uA-50uA.

I have made a precision power supply and have tried to ad a current limiter, I have also tried to use a current divider but with no great result.
At the moment do the power supply deliver 5V 1A but it can be changed.

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#### jan.didden

Paid Member
A resistor of 10k between the 5V and the 1.4V input of the opto conducts max current of 0.36mA.
For 100k it is 36uA. So a pot of a few 100k with a fixed resistor in series to limit the max current will do it.

Are you sure about the 50uA? Isn't it 50mA?

Jan

#### FriedMule

A resistor of 10k between the 5V and the 1.4V input of the opto conducts max current of 0.36mA.
For 100k it is 36uA. So a pot of a few 100k with a fixed resistor in series to limit the max current will do it.

Are you sure about the 50uA? Isn't it 50mA?

Jan
Thanks, yes it sounds low but the schematic states that min(berly on) is 0.1uA to max(full on) 50uA. they demands 1.2V min and 1.4V max.

Sorry for this noob question but to me does it sound like an extremely low current to adjust via a pot, would it not be more "stable" to let a higher current go trough the pot and then "divide" it afterward?

#### PRR

Paid Member
> it sound like an extremely low current to adjust via a pot, would it not be more "stable" to let a higher current go trough the pot and then "divide" it afterward?

Pots come in very high values. Figure out the simple way, then look to see if it has practical problems.

Show us this coupler and the current limiter.