Does this UVLO circuit work in the real world?

[PeLa]

Hi there,

I've been struggling trying to figure out how to set up an UVLO for a 7 cell Lithium Ion Battery (max 30V, with a 21-22V cut-off).

What "I" have come up with is pieced together from various different sources. I am a bit insecure about it. Something does not look right...
The SPICE simulation looks ok to me (see below). It should turn off at around 21-22V.

The N-channel MOSFET that I have chosen should be able to handle that the current (2-8A).

Let me know, if this is complete horsesh** and doesn’t make sense at all.
Cheers,
Pete

[PeLa]

PS: Here's the design I tried to adapt.
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http://ww1.microchip.com/downloads/en/DeviceDoc/50002561A.pdf
I want the Mosfet to switch off my load, when the supply voltage drops below a threshold.
It looks like it does that in the simulation, but I am not sure why it works.

[Ian.M]

  as there's no emoj for a reeking pile of s--t being circled  by a dark cloud of flies.

If you sim something in LTspice its generally a good idea to post the .asc file and if it uss non-standard parts,  zip it it up with the 3rd party models and symbols required.

See if you are quite so happy after adding:

Code: [Select]

.step temp 0 75 25to the sim!

Also what about the approx 25W dissipation in M1 at max. load?

[PeLa]

Thanks!
Oops. Temperature... that's not gonna work. I don't think I need to attach the components after running the sim at different temperatures.
Can you point me in a direction how to do undervoltage lockout of a 30V source in a less stupid way?

[T3sl4co1l]

The NMOS is a source follower, so it will always drop a few volts when "on".

You need a low-side switch, or a PMOS and complementary enable (active low).

Have you considered a battery management IC instead?

Tim

[PeLa]

[...] PMOS and complementary enable (active low).

Have you considered a battery management IC instead?

Thanks. Battery Management IC. I believe that's the keywords I needed.
Looking into them now. Also thank you for the explanation!