Does Anyone Know How to Change X-Drive Setting With Resistors?

[scumbagatheist]

Hi All. I've got a couple of the X-Drives, preset @ 290mA. I'm using them for a couple of 2 cell PL520 builds, and would like to get a little more current out of them.

Does anyone know which resistors are the set resistors and what the formula for calculating current with this switch is?

Thanks all.

 

[Cyparagon]

I don't know anything about the X-drive, but this method will work with all constant current drivers you are unfamiliar with:

The sense resistor will be of low value and therefore easy to find. Usually <1Ω, but possibly a bit higher for lower current settings. First calculate the feedback voltage using ohm's law: you have current and resistance, you can get voltage. The driver will drive the output until it sees this voltage on the sense resistor, you see. So set up a new ohm's law equation with the known feedback voltage and plug in the current you want. Solve for the new resistance.

 

[jander6442]

I believe these are the ones to be set.

 

[scumbagatheist]

Cyparagon, thank you again for your mathematical assistance. By 'feedback voltage', do you mean the combined Vf of the diode and the driver? When you say I have current, I assume you mean the current output of the driver. But, resistance? Am I just using the sense resistor for that variable in the equation?
I've found two lower resistance resistors:
R4 = 1R47
R5 = 2.0
I think I'm getting close...

 

[Blord]

The formula is .25/R=I

R4 = 1R47 --> 170mA
R5 = 2.0 --> 125mA

The total is 295mA.

 

[scumbagatheist]

ahh...so, .25 is the reference voltage? Thanks Blord. You're great. Now...I just doubt I can get a small amount more w/ the resistors I have on hand. I don't want to go above 315mA.

Rep for all if it lets me!

Edit: thanks again everyone...now, if I can just find a 1.8ohm resistor, I can get the 310mA I'm shooting for. If it proves to be more than just an exercise in CE analysis, I'll leave it alone.