On Thu, Feb 13, 2003 at 11:30:05AM -0800, Robert Ritchey enlightened us thusly
> Declan,
> This is my problem. My client already uses regulated 5V wall-warts for his
> USB hub rated at 2.1A. He wants to use the wall-wart for the device I just
> designed. Actually I just got PCBs back today, no protection. Anyway, it
> uses all 5V and is not tolerant of anything less than 5V. I can't get away
> away with 4.5V or 4.6V using a LDO regulator rated at about 1A or 1.5A
> (most LDOs of this size have 400mV-600mV dropouts at rated load).
> Scare tactics don't work here, I will just lose my work if I start arguing.
> I
> came too close a year ago arguing a digital fact I knew a lot about. I need
> the work, not much else out there right now.
That's worth a lot more than theoretical nuances. If you have the pcbs
back, and give up on the triac circuit, and other suggestions, just put
in the tranzorb. The max breakdown voltage is is 6.8V, they'll take a good
whack in reverse and they save 5V circuitry. One circuit I got to know had
THE WORST pcb ever, and 24V inputs with motor noise & mains spikes. Some
dweeb put in the tranzorb because RS were out of zeners. It killed a lot of
the crap on the 5V line, and saved the chips when regulators or power
supplies gave out. He didn't need reverse protection, but did need over
voltage, because the cheapo power supplies had a "5V" line that wandered
depending on the current :-/.
--
With best Regards,
Declan Moriarty.
--
Author: Declan. Moriarty
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