Love the Femtobuck, but for my project I want to have it adjusted to a fixed current different from the preset of 0.333A it comes with. I know I can use the 0.5-2.5V in to regulate but I wonder if I can just replace R2=0.3Ohm with a different resistor to 0.6 Ohm to lower it to 0.15A? If yes, where are the limits to that?
Also which one is R2? The inner or the outer one?-)
Thanks, G
If I am reading the schematic correctly I think you are correct. If you reduce the output current by 50% you would want to double the resistor value of both resistors. This is what the hook-up guide says about increasing current output:
“If even 660mA isn’t enough current for you, it is possible to increase the maximum current of the FemtoBuck board up to 1A per channel. To do so, replace the current sense resistors with smaller values. To calculate the new value for the resistor, use this formula:”
So I think changing R1 and R2 to 0.6Ohm while combining them should work, however, I am not 100% sure.
I think if you use your DMM and do a continuity test see which one is currently tied to VIN. Than should say which is which. I feel like the left one is R2 as I don’t see it have a direct connection to the jumper like the right one has.
Hope this helps.
Good points, I will try and report. If I fry one thats ok as I bought a few - just in case …
Quick test : R2 is the inner one, and yes one can adjust the max current by adjusting R2, at least for the few combinations I tried. Will get a pot to be flexible moving forward.
Will report back if it breaks at one point … G
R2 is the current shunt; all of the load current must pass through it. Keep that in mind when choosing the potentiometer. It won’t be easy to find an (affordable) low resistance high power pot. You would be looking for something in the 1-2 ohm range capable of 1A current or so.
/mike