[sdiy] SSM2164 last time buys

[Scott Juskiw]

The first thing I thought of was a relay based solution, but that seemed a bit overkill for one PCB. I was hoping there was something simple that could be built onto a PCB with a few cheap components, rather than a system wide solution.

>> Last week I was thinking of a way to
>> enforce a both-rails-or-neither rule.
>> 
>> Resettable fuses in thermal contact might or might not work. The
>> best solution I've found is a DPST 24 V relay, of the normally
>> open type, driven by both rails in series. Bad idea ? You tell
>> me.
>> 
>> Probably not suitable for protecting individual modules as
>> relays draw not insignificant current.
> 
> A decent system-wide method would be good if you have a known 5V
> supply. You set comparators for both +V and -V rail and feed those
> into an AND gate which uses a common line to turn on and off a pair of
> MOSFETs in series with the +/-V rails. Only when both +V and -V rails
> are stable and happy does the logic circuit turn on the FETs. Of
> course you'd need a pair of gate drivers as well to make sure they
> clamp on and off, but that's a small price to pay system-wide.
>