This project came about from my need for a light source for my Franken-ebay stereo microscope. I will have another instructable that will cover using this driver / dimmer card in a fiber optic setup. It is now available here:

Main design goals for this project were:
  1. Small size
  2. 10 dimming levels + off
  3. minimum 10W power handling 
  4. Fan control (on/off + PWM)
 Board files, logic, firmware, and source code can be found on my web page here

Here is a video of me taking the prototype card though it's paces:

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Step 1: Some math

Picture of Some math
Before starting the build there is a little bit of math required to select the LED, LED current limit resistor, and power supply. 

LED selection:
This circuit can drive either a single led or a string of leds as long as they fall under the following conditions:
  1. Max forward current of the string is 1A (1000mA) or less
  2. Max forward voltage of the string is 24.5V or less

LED current limit resistor:
The CAT4101 datasheet includes the following table for setting LED current. 
LED current in mA current limit resistor value in Ohms
100mA 4990 Ohms
200mA 2490 Ohms
300mA 1690 Ohms
400mA 1270 Ohms
500mA 1050 Ohms
600mA 866 Ohms
700mA 768 Ohms
800mA 680 Ohms
900mA 604 Ohms
1000mA 549 Ohms

Power supply selection:
There are 3 conditions the power supply must meet to be used with this driver.
  1. Unloaded voltage (floating / LEDs off) less than 25V
  2. 0.5V greater than max LED (or string) voltage
  3. Less than 6V over the LED (or string) voltage when LEDs are on) 
  4. Output current of the power supply is greater than the forward current of the LED (or string) + 100mA

In my case I am using a LED with a on voltage of 10V to 12V and a forward current of 1A (1000mA) (this is from the LED data sheet)
12V is less than 24.5V so ok there. 
1A (1000mA) looked up in the current limit resistor table results in a 549 Ohm resistor
12v (LEDVmax) + 0.5v = 12.5v is the minimum output voltage that the power supply can put out and be usable. 
10V (LEDVmin) + 6V = 16V is the maximum output voltage that the power supply can put out and be usable. 
1A + 100mA = 1.1A is the minimum output current that the power supply can put out and be usable. 
In my junk pile I happened to have a 16V @ 4.5A power supply from an old laptop. This meets all the requirements calculated above for the LED I picked. 

GrfxGawd9 months ago
This is quite, enlightening.
I'm working on a 5A laser diode driver using the PIC12F752. The requirements are a bit more stringent than driving an LED. I hope you don't mind if I examine your source code. :D
wireb (author)  The Lightning Stalker9 months ago
Follow the link to my website all the source is in the zip with the board file. FYI the pic on mine just handles the PWM control for dimming. All the current control is handled by the CAT4101 so even if the PIC goes haywire the led will be fine.
apalacios29 months ago
Where did you get that Kearsarge 522 Laboratory Timer?? I want one!! Nice article. Just what I needed!
wireb (author)  apalacios29 months ago
Actually found it in the trash back in school. Needed to be cleaned out but once that was done has worked since. If anyone ever sees a manual for it let me know. Looked on and off over the years but never found one online.
apalacios2 wireb9 months ago
WHAT!? In the thrash!? You are so lucky, man! If I ever come across a manual for it, I'll let you know.
wireb (author)  apalacios29 months ago
It was in really bad shape not sure what the stuff was they dumped on it but was sticky and really gummed all the buttons and switches up. Took me a few weeks to take everything apart and clean the goop out.
apalacios29 months ago
You never show the LED you chose. Any details?
wireb (author)  apalacios29 months ago
If you follow the link to the fiber light post at step 2 had the information on the LED. I used a DC-LE14274 from sure electronics in that application. Wrote this instructable up to be more generic so folks could use this driver with any led or string of leds that fell under the 24.5V @ 1A maximum.
apalacios2 wireb9 months ago
Cool! Thank you!
audreyobscura9 months ago
"Franken-ebay stereo microscope." Perfect.