Electronics > Projects, Designs, and Technical Stuff

LT3045 crowbar

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Geoff-AU:

--- Quote from: gman76 on July 08, 2022, 08:07:52 pm ---Why not use an OV/UV supervisor, like the LTC2912?  Use it as an independent circuit that monitors Vout.  You can tie the /OV pin to the 3045's EN pin.
--- End quote ---

If the LT3045's pass BJT failed short circuit for some reason, fiddling with the enable pin isn't going to do anything useful.

nealix:

--- Quote from: Terry Bites on July 01, 2022, 11:08:59 am ---As noted you cant rely on the LT3045 to trigger a crowbar. You can improve the trip point accuracy and speed by using a TL431 as a precision comparator. A small PNP inverts the 431s output and provides plenty of gate current. C1 creates a miller integrator to filter out fast transients and prevent false triggering. Icrowbar is for illustrative purposes.

R1 R2 set the theshold.
Vt= (1+R2/R1)*Vref
Vref=2.5V for the TL431.

--- End quote ---

I like what Terry shows above, but due to 10 ohm sense resistor and BJT, it is not going to be great for much current in a load.
But the idea is widely used;   Rather than a crowbar and fuse, which places stress on the power supply parts and is slow, a lot
of people, even in commercial products, are now using a fast comparator and MOSFET switch to OPEN the load rather than short
the power supply.   I use two 40 amp DC load distribution bars that have the MOSFET and comparator built in.   When I dial up
the output voltage on the 50 amp power supply, the moment it hits the trip point everything simply turns off.   No blown fuses.

Neal

Geoff-AU:
MOSFET to open the load works great and less destructive, as long as you aren't in danger of overvolting the MOSFET.  If you are, adding an extra fuse/sidactor on the input would be an easy protection method that would only activate if things got really bad.  (you can get some properly impressive MOSFETs these days though, so it's unlikely you'd need to).


matthuszagh:
FYI Based on the interesting discussion here I asked another question concerning a comparison between the crowbar and comparator + MOSFET approaches (https://www.eevblog.com/forum/projects/comparison-of-overvoltage-protection-methods/).

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