Hello,
I'm hoping someone can help me.
I have a broken light source on a microscope that I wish to replace with an led source.

I am planning to use an Osram powerstar that produces 280lm at 700mA with a forward voltage of 2.7-3.2V

I was proposing to drive it with an RCD-24-700 with analogue dimming using a logarithmic potentiometer of 10K.

I'm wondering is the circuit below correct? I based it on the RCD series datasheet but the example they give uses the vref version of the RCD-24 which I do not have.


Thank you

 

I see no reason why it would not work correctly, connected as shown. My only question is; why did you choose the 700mA version? At that current, the LED will light up the whole room!

 

Thank you for the reply.

I selected it based on this webpage

http://www.frankshospitalworkshop.com/electronics/diy-led_microscope.html

Intially they went from halogen to led but in the end, they upgrade from a led running at 350mA to one at 700mA, so it seemed like a good idea to just go with 700mA from the start.

They based their supply on a voltage divider and transistors but it seemed handier for me to just use a RCD-24 albeit a little more expensive.

 

That is an excellent posting. He mentions that a 1W LED will give about the same amount of light as a 20W light bulb. I made one myself, several years ago, using a low powered white LED with a current of 20mA, giving a total power of 60mW. It works very well.