Alex Zoghlin <[email protected]> writes: > I was going to respond and say this is something that is pretty easy to > test, but I think Casey beat me to the punch with a bit of empirical > evidence. If you look at the RRC2/3 series altimeters, they contain a big > capacitor specifically to continue to provide power in the case of a > brownout that used to happen on their old altimeters when the right > combination of ematch and battery created an extreme short that exceeded > the batteries limits, including 9 volt batteries.
Big electrolytic capacitors are a mechanical disaster, and a potential point of failure in and of themselves. So the "more cleverer" solution we came up with years ago and use on everything now is to put a diode and relatively small ceramic bulk capacitor in front of the LDO. This allows the LDO to ride through short interruptions. Then we use a comparator to watch the voltage at the LDO input, and when the cap has discharged to the point where the LDO output will soon start to droop, the comparator briefly disables the pyro channel. That "removes the short", the bulk cap rapidly recharges, and then the comparator allows the pyro channel to turn back on. The idea is that we're putting as much energy into the pyro device as we can without ever allowing for the possibility of a brownout, until the battery is fully discharged. We choose the size of the bulk cap to ensure a pyro channel with a dead short will see well over 90% "on" duty cycle. With a normal e-match, the match will fire in the first "pulse" well before the comparator trips in, so all of this is irrelevant. An upper-stage igniter or something that needs more joules can get them across multiple "pulses" from the pyro circuit. This is why I don't think the effect being seen is a "brownout" in the traditional sense. It's certainly true that a separate pyro battery means this circuit will never become part of the equation. However, separate pyro batteries also add complexity and more potential points of failure. There are no free lunches here... And, of course, it's always possible there's something going on we just don't understand yet. If you think so, please please please quote the hardware and firmware version so we don't waste time and can get right to thinking about possible explanations. Regards, Bdale
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