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Well, Dang, It Doesn't Work

A project log for Affordable Reflectance Transformation Imaging Dome

A simple and inexpensive way to image and analyze subtle surface details on objects.

Leszek PawlowiczLeszek Pawlowicz 11/10/2016 at 00:450 Comments

Logged about a possible alternate approach to the low-side LED matrix driver, where I use n-channel MOSFETs to switch on the LED, and a single CAT4101 to gate/control the current running through all the n-channel MOSFETs. Seemed to work fine at low to moderate currents, so I thought I'd prototype the low-side driver board using this design (cheaper than my original, and easier to work with). Before I did, I thought I should probably check it on a breadboard at the maximum current of 1A. Well, it doesn't get to 1 A; the best I could do was 0.8A, which is probably OK for most applications, but I still want full power. I suspect that there's some issue with the I-V characteristic of the MOSFET that's causing the current to saturate prematurely at a lower level. I may revisit this at some point in the future, but for now, the low-side driver board design will stay fixed with 8 CAT4101s both switching the LEDs in the matrix rows and controlling the current.

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