Setting up to do some higher power load testing. A long time ago I built a 0-20V +/-120A sync buck unit, working with a 24V (lead acid) reservoir, with CC/CV/programmable behavior. Well, that's great if I'm powering loads big or small, but strong sources can easily overwhelm the battery (I have a pair of 12V 122Ah deep cycle batteries hooked to it), particularly if it's discharged a bit (between float cycles) so the ESR is high. (The converter unit is protected against overvoltage, it simply turns off if its input rises too high -- OVLO. But that's obviously a non-starter for sustained operation.)
So I'm making a load dump to wire in parallel with it:
https://www.seventransistorlabs.com/Images/ShuntBallast.pdfSimply a shunt regulator, with switches into fixed resistors, so, hysteretic control. Quite straightforward.
The relatively large capacitors guarantee that the cycle time is no faster than a few hundred microseconds; and they need low ESR (ca. 17mΩ ea.) so that the zero in the transfer function doesn't increase frequency a dangerous amount.
Here's typical operation with a 10 ohm load resistor and a moderately soft rectified supply:
Switching is quite well behaved, given the modest drive strength. (An emitter follower is needed, to save on pulldown resistance, but otherwise things are quite relaxed.)
Note the overshoot due to the inductive load resistor, clamped by the TVS. I've actually got SMCJs in here (handy), but SMAJ is more than enough.
Now to build the frame to support the resistors, and, well, the rest about the power supply I'm going to test with it...
Tim