13 – square-inch version works ✔

A project log for Universal undervoltage lockout up to 34V input

Feature-packed over-discharge protection. Set the cell-count, minimum cell voltage and dip-time below threshold. Fully hackable!

JanJan 09/18/2019 at 07:070 Comments

Update 2019-10-03

finally working version - see the 10 ohm resistor :)

Phew, that was a journey. This project really started killing me slowly... It worked at first but the damn thing tried to die randomly. As I put a 5V6 zener directly into the 5V rail (the reg. has a short circuit current of 20mA only so the zener does not need an resistor) at least the Attiny861 follow the regulator each time it blew...

I tried everything and always thought: Ah, this works now. UNTIL it blew again. Mostly on (re)connecting the LiPo battery. So it had something to do with the inrush current.

When I talked with @Simon Merrett about the issue, he suggested to limit the inrush current to the regulator with a resistor. First I though this is a bad idea because additional resistance in the path means more (quiescent) current.

But I gave it a go. In the above picture you see a 10 ohm botch-resistor. It effectively kills the inrush-current to something which doesn't destroy the regulator.


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Just tested the board with a 6S LiPo and a electronic load. You can switch a constant 175-180W without the MOSFET getting more than luke warm.

Off-current is 13µA. A bit much for my taste (should be more like 5...8µA) but I guess it's got something to do with the reverse leakage from the 5.6V protection zener (though the datasheet says 2µA reverse current max...).

I'll do some more tests soon.