What about a soft start circuit? LTC makes one that first watches the input voltage ramp (divider circuit) and then controls the gate to a FET, and if the voltage drops, it shuts off the FET.


--- On Thu, 10/2/08, Alan B. Pearce <Alan.B.Pearce@stfc.ac.uk> wrote:

> From: Alan B. Pearce <Alan.B.Pearce@stfc.ac.uk>
> Subject: Re: [EE] Undervoltage crowbar circuit
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Date: Thursday, October 2, 2008, 1:21 AM
> >What I'm after is something that will when the
> voltage droops to a
> >set point basically short the cap and de-energise the
> system.
> >Physically small is a constraint. An easy to use IC
> would be nice.
> 
> I would be very tempted to use a switching regulator to
> supply the 
> electronics, with some form of analogue comparator on the
> battery to signal 
> the low voltage condition to the electronics. Having the
> switching regulator 
> will ensure that the electronics has enough volts present
> the whole time to 
> make the thing go safe in a controlled manner. 
> 
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