Lack of over voltage protection in programmers - Page 1
Forum section: electronics / general

author: vvanders
author_rank: Regular Contributor
timestamp: December 25, 2012, 04:05:04 am
content: Was doing some experimentation w/ some 6v battery configs with my AVR, didn't realized that my AVR Dragon was connected to my VCC until I saw the puff of smoke and smell of burnt electronicsWould it hurt companies to put just some marginal over voltage protection in their programmers? I'm sure I'm not the only one who's done this before, now off to order another Dragon...

author: zaoka
author_rank: Frequent Contributor
timestamp: December 25, 2012, 04:14:35 am
content: Its not designers, its investorsTheir mantra is always "Save"

author: cwalex
author_rank: Frequent Contributor
timestamp: December 25, 2012, 04:30:51 am
content: AVR dragons are known for their habit of letting out the magic smoke. At least they were, I don't know if they fixed the design but there were lots of people experiencing it when they first came out.

author: Unknown
author_rank: Unknown
timestamp: December 25, 2012, 09:11:22 am
content: The more expensive programmers aimed at professionals (eg. the various incarnations of the JTAGICE) tend to have beefier input protection. The Dragon was obviously an attempt to offer the most bang/buck with very aggressive cost optimizations (not even budget for case, cables or headers).Plons from avrfreaks.net has designeda buffer circuit between the Dragon and the DUT. This was a simpler version ofwork done by KKP. An alternative approach isusing opto-couplers.If you want Atmel to do this work for you, then you clearly need to pay them the extra $50 or so for a JTAGICE Mk. 3 (assuming you use AS6). I haven't studied the protection circuit for the JTAGICE Mk. 3, but it was quite decent in the JTAGICE Mk. II.

author: vvanders
author_rank: Regular Contributor
timestamp: December 25, 2012, 09:09:43 pm
content: Thanks for all the detailed information, I figured the JTAGICE3 had better input protection but wasn't sure. I think I'll pick up one of those this time instead of another Dragon.

author: ptricks
author_rank: Frequent Contributor
timestamp: December 26, 2012, 12:33:23 am
content: After having replaced enough parts over the years there are a couple modifications I do to any new hardware like programmers.1. Zener on the input to shunt anything over the voltage it requires, if the zener blows I don't care and it is enough time for me to notice the problem. Could put crowbar circuit, but the 1W zeners have served me well over the years.2. Reverse power connection protection using a diode - started doing this after I got some china USB cables that had the + on the black wire and the - on the red wire, that screw up cost me some LCD displays that burned out from the wrong polarity.3. Current limiting all my test gear connections. Current limiting parts are so cheap now that it just makes sense. If you know that a programmer only needs 50ma don't rely on the hope of nothing going wrong and it powered by a 5A supply.4. Anything that interfaces with 3.3V and not 5V or 1.8V and not 3.3V, I install buffer or level converter chips. In the past with that kind of stuff , I added it if what I was working on needed it. Like using chips where some ports are 5V compatible, but others are not I would just use the 5V ports, I'm not using the 3.3V ports that burn out at 5V so why bother ? I bother because I learned that something always finds its way onto the other pins where it doesn't belong and kills the 3.3V part.