In earlier questions I raised a problem about a DC-DC booster that destroyed itself when its load was disconnected by drawing a large current from its input power source. This was specific when using Lead-Acid batteries (probably because a LA can deliver a large burst).

The task was (for me) to find a current-limiter solution on the input. I have tried a simple solution with a resettable (push) fuse, but that is too slow.

I have then found this device, based on a Allegro current sensor ACS712.

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With this I can get a corresponding voltage reading from its current flowthrough.

So here we go. How do I use some external discrete components to activate a relay that disconnect the input power to the DC-booster? I know about electronics - but not that much. My simple guess is a zener that controls a transistor that powers the relay. But it must be good (with good I mean quick acting) and reliable.

From the curve, I can see that the wanted breaking point is around 3,2V at 6-7Ampere (It must break from 6A and up).

Below, links to my earlier questions about this problem

Fuses - Are there any voltage conversion for the break-off

How to prevent large inrush current without a reset-fuse

DC-DC booster fails with lead-acid battery source


simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ NTC (+relay) didn’t work out for you? \$\endgroup\$ – winny Jul 12 '18 at 14:50
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    \$\begingroup\$ NTC’s are also called ICL protective chips \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 12 '18 at 14:57
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    \$\begingroup\$ An NTC (stands for negative temperature coefficient) starts out at higher resistance when cold to limit the current. As it heats up the resistance drops to avoid excess losses. So yes, it "is about sensing temperature" (its own) and it is not "too late" because it STARTS at higher resistance. \$\endgroup\$ – John D Jul 12 '18 at 15:16
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    \$\begingroup\$ Diode is reversed. Put it with cathode upwards \$\endgroup\$ – Gregory Kornblum Jul 12 '18 at 18:18
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    \$\begingroup\$ Stop scratching for thermistors. You can find NTCs for inrush current limiting for almost any arbitrary value. \$\endgroup\$ – winny Jul 12 '18 at 19:13

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