Here's one I use that I don't think has been suggested. I use a MOSFET in series at the input, arranged to switch off on over-voltage. I didn't notice what current your circuit draws, but if you use a T0220 with a few milliohms resistance you get only a few millivolts drop when on. Because you switch it off on over volts, no power is dissipated. Use something like 100V device and it's bulletproof.
To protect against reverse voltage you have little choice other than a reverse diode across the input. BTW What is the total current drain of your circuit? On Thu, 13 Feb 2003 11:30:05 -0800 Robert Ritchey <[EMAIL PROTECTED]> wrote: > 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. > > At 09:45 AM 2/13/03 -0800, Declan. Moriarty wrote: > >I had backed out of this one, but now feel like getting back in. A triac is > >an A.C. device, with two scrs back to back. Why is it suggested as a > >crowbar? Probably in case you had an A.C wall wart. Personally, I think > >it's not the way to go at all. The idea with a triac is that you control > >A.C. I would use an SCR if you have to have a crowbar. I would never try > >to fire one with simply a zener. Gates get sensitive in the heat ... > > > >You are going to fart around and lose a week with the triac unless you > >find an application and copy it. > > > >Have you considered a low drop regulator? I recently used a LP 2981 > >which is guaranteed max 0.1V drop at full load. Put a schottky in > >series, use a 6V supply and you're smiling. You may just need a little > >more bottle with whoever is telling you to use a 5V regulated external > >supply, which leaves your circuit exposed. Tell him it cannot be done > >safely. He must hold his face up if/when the solids hit the ventilation > >as his part of the design goes down the tubes. Write a memo warning them > >- that is a great scare tactic, and your backside is covered. > > With best Regards, > > Declan Moriarty. > > -Bob > -------------------------------------------------------------------- > Robert Ritchey > Quest Engineering & Development > 1328 East Cottonwood Lane > Phoenix, AZ 85048-4765 > Tel: (480) 460-2652 > FAX: (480) 460-2653 > E-Mail: [EMAIL PROTECTED] > E-Mail: [EMAIL PROTECTED] > E-Mail: [EMAIL PROTECTED] > E-Mail: [EMAIL PROTECTED] > WWW: www.QuestEngDev.com/ > WWW: www.Smart-Fly.com/ > -------------------------------------------------------------------- > > -- > Author: Robert Ritchey > INET: [EMAIL PROTECTED] > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > San Diego, California -- Mailing list and web hosting services > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). -- Author: Peter Vogel INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
