yngndrw
New Member
Hi,
I would like to build a quick and cheap adjustable current regulator for LEDs.
I have a LM317 here so it would be nice to be able to use this. The problem is that I want to be able to drive both 0.5W LEDs and 10W LEDs. (As well as anything in between.)
The 0.5W LED requires 150mA and has a voltage drop of aprox 4V.
The 10W LED requires 1.5A and has a voltage drop of aprox 8V.
Therefore I need a 0 -> 1.5A adjustable current source powered of a 12V supply to make things nice and easy.
I worked out the resistor required for both of these LEDs. The 0.5W LED requires around 8Ohms and the 10W LED requires around 0.8Ohms. The problem is that the resistor needs to be around 3Watt in order to cope with the 10W LED. (It comes out at 1.8W if I use V * I and 2.8W if I use I^2 / R.)
Obviously this would be unreasonable to expect from a variable resistor, so what can I do ?
Thanks,
-Andrew.
I would like to build a quick and cheap adjustable current regulator for LEDs.
I have a LM317 here so it would be nice to be able to use this. The problem is that I want to be able to drive both 0.5W LEDs and 10W LEDs. (As well as anything in between.)
The 0.5W LED requires 150mA and has a voltage drop of aprox 4V.
The 10W LED requires 1.5A and has a voltage drop of aprox 8V.
Therefore I need a 0 -> 1.5A adjustable current source powered of a 12V supply to make things nice and easy.
I worked out the resistor required for both of these LEDs. The 0.5W LED requires around 8Ohms and the 10W LED requires around 0.8Ohms. The problem is that the resistor needs to be around 3Watt in order to cope with the 10W LED. (It comes out at 1.8W if I use V * I and 2.8W if I use I^2 / R.)
Obviously this would be unreasonable to expect from a variable resistor, so what can I do ?
Thanks,
-Andrew.