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In another question (DC-DC booster fails with lead-acid battery source) I described a problem with a DC-DC booster that destroyed itself by dragging a large current when its output was disconnected.

This did not happend when the power source was a sw-mode (maybe due to its overload circuit), but when a Lead-acid battery was used who could deliver large burst current (>40A).

Apparantly this is a consequence of the DC-booster design. So I need some shut-off circuit which could be a resettable fuse, but I think that this is somewhat a primitive solution.

Maybe its possible to use some power FET, but im not much into how to design control a shut-off state at, say at 8A - and certainly not to make it well working.

Gearlos
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  • Unless he can implement a soft start in the regulator a solution could be an “ICL surge limiter” for startup only but for cutoff UVP is needed or switch the input to Reg – Tony Stewart EE75 Jul 04 '18 at 15:44
  • Resistor + relay. But soft start is way better. –  Jul 04 '18 at 15:47
  • Inrush? Maybe flyback protection from inductive wire current? – Tony Stewart EE75 Jul 04 '18 at 15:49
  • I could put another of the same DC-booster in front of the original that could limit the current of the original that want to destroy itself (both have pots for controlling the current). The front DC-DC will never have its output disconnected as it feeds the original ;) – Gearlos Jul 04 '18 at 15:55
  • Or maybe a couple of LM317 in current limiter mode. I think I can remember this shown in the fab. specs – Gearlos Jul 04 '18 at 16:00
  • No 317! Google boost inrush current and you will find plenty of examples. My precious design had NTC+relay in parallel and a by-pass diode over the entire boost converter to take the hit there to the output cap. – winny Jul 04 '18 at 16:03
  • yaya - But its not inrush current I want to prevent, but disconnect-rush (or is it the same) – Gearlos Jul 04 '18 at 16:09
  • It seems to me that the main problem is the converter doing something odd when you disconnect the load - does the converter have a schematic or data sheet? – Andy aka Jul 04 '18 at 16:24
  • Andy - It a cheap china PCB build with a Texas PWM chip. It is smart and works very well (96% efficency) but have this "little" flaw. I guess its just not complete with protection and probably intended for use with sw-mode as power source. So its no that "odd" other than You need to add some limiter when using LA batts. – Gearlos Jul 04 '18 at 16:52

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