LT3083 current limiting


Posted on Feb 6, 2014

I`m using regular analog control via pots, though will use digital readouts of voltage/current. Anyhow. I HAVE watched the PSU videos, but at least in simulations I couldn`t get the single-LT308x with the transistor limiter to work properly (one, it didn`t go to 0, so a shorted output causes >2 amps to flow! - and two, it tended to oscillate a bit now and then). I`ve almost decided


LT3083 current limiting
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to go a simpler but more expensive route and simply use two LT3083s. I attached the LTSpice circuit, though without the MAX4080T current sense amp, since that component is in a separate file on my computer. It didn`t affect these questions whatsoever, though. Also, note that "Iset" and "Vset" are potentiometers wired as rheostats; I model them as resistors in LTSpice since there`s no built-in pot component. In each case, they`re controlled by a 50 µA current from the LT3083. What I`d like to do is to use Rlimit (0. 5 ohms) as the current sense resistor (with a 5x gain amp instead, of course), to eliminate the extra 250 mV drop over Rsense at the output. The reason I "can`t" right now is that there is a lot of ripple between the regulators when the current-limit mode isn`t active; the left LT3083 simply outputs as high a voltage as it can, which lets the input ripple through unchanged:




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