I am trying to build a supply-voltage supervision circuit based on the design suggested in 2nd answer here (the one with the CircuitLab schematic): What is the simplest way to turn off some circuit when supply voltage reaches a minimum level?

I do not have much of an electronics background so I cannot say if the suggested solution might already be flawed or if I just picked unsuitable components for the voltage range that I am interested in:

As compared to the original thread, I am trying to build a circuit that shuts down supply voltage at a minimum threshold of around 3V while switching through anything bigger, up to around 5V (the goal is to replace my uP's built-in brown-out detection with something that draws less power).

I am using a DN1509N8-G (see http://cdn-reichelt.de/documents/datenblatt/A200/DN1509_DS.pdf) for M1 (same as in original schematic) and a MAX810-T (see https://datasheets.maximintegrated.com/en/ds/MAX803-MAX810Z.pdf) for U1 (which - as I have verified - outputs any input voltage smaller than 3.08V "directly" on its RESET pin but switches the RESET to 0V as soon as 3.08V is reached/exceeded.. the MAX810-T has a push-pull output and I am therefore not using an R1).

When measuring the OUT voltage (at drain of M1) I do not get the desired switching behaviour, i.e. 0V for any input below 3.08V and original input voltage for anything above 3.08V - instead I always seem to get roughly the same voltage which is input (at least in the range from 2-4V) somewhat lowered by some kind of forward voltage drop. It seems that M1 does not provide the desired functionality - at least with the voltages that I am dealing with.

What would I need to change (and how) in order to make this circuit work within a voltage range of 0-5V with shut-down threshold of ~3V?


My bad!

That's actually my error in the post, thanks for catching it! I had the FET connected with D and S swapped so the body diode was forward-biased instead of being reverse biased. So, swap D and S on your FET and the circuit should start working.

  • \$\begingroup\$ You probably should explicitly annotate where D and S is on your schematics. G is always clear, but D and S are always confusing. \$\endgroup\$ – Ale..chenski Dec 6 '17 at 1:48
  • \$\begingroup\$ Just switched D and S and now the circuit does switch - but just the wrong way: supply voltage is switched off when at least 3.08V are reached. (I had earlier switched from MAX809 to MAX810. According to the specs I had felt that it would be the correct version to use. Now I guess I'll revert back to the MAX809 and see what happens.) \$\endgroup\$ – wothke Dec 6 '17 at 11:21

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