Big crowbar module for <4VDC?
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From: John Devereux on 20 Dec 2008 10:49 Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: > On Sat, 20 Dec 2008 15:10:11 GMT, Jan Panteltje > <pNaonStpealmtje(a)yahoo.com> wrote: > >>On a sunny day (20 Dec 2008 10:06:18 GMT) it happened Jasen Betts >><jasen(a)xnet.co.nz> wrote in <giig2q$kmd$7(a)reversiblemaps.ath.cx>: >> >>>On 2008-12-19, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >>>> On a sunny day (Thu, 18 Dec 2008 18:32:11 -0800) it happened Joerg >>>><notthisjoergsch(a)removethispacbell.net> wrote in >>>><TID2l.10279$yr3.2278(a)nlpi068.nbdc.sbc.com>: >>>> >>>>>> http://www.hobbyprojects.com/thyristor_triac_and_diac/thyristor_as_a_crowbar.html >>>>>> >>>>> >>>>>Has the author ever heard of a gate trigger voltage? Assume 1.5V for >>>>>now: Zener 5.1V plus Vgt = 6.6V. Phssst ... crackle ... pop ... *BANG* >>>>>... there goes the majority of connected logic chips. Many of those >>>>>won't take anything above 6V. >>>>> >>>>>The proper way to do a crowbar is with a TL431. >>>> >>>> Crowbars are to protect the LOAD, not the supply, and should be at the OUTPUT. >>>> In case of a 100K$ load and a 100$ supply, the choice is easy. >>>> Shorting before the regulator does not guarantee energy in any caps and >>>> or inductors in the circuit does not make it to the load. >>>> Simple. >>> >>>You can put the crowbar SCR across the input to the regulator and the >>>over-voltage detector across the output - a kind of feedback. >>>I suspect that is how Jim designs his. >> >>Yes you can do that, and he even showed a small kid diagram with a 7805 IIRC. >>But that will _not_ protect what happens on the supply line. >>Jimmy has the typical rightist republican thinking: >> His method protects his own design, not the load :-) > > Jerk, Learn to read. AND: I DIDN'T post any diagram. AND: It DOES > PROTECT the load... some people here are just TOO STUPID to understand > simple solutions. I suppose it would not protect the load against externally- or load- generated overvoltages. -- John Devereux
From: Jim Thompson on 20 Dec 2008 11:14 On Sat, 20 Dec 2008 15:49:59 +0000, John Devereux <john(a)devereux.me.uk> wrote: >Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: > >> On Sat, 20 Dec 2008 15:10:11 GMT, Jan Panteltje >> <pNaonStpealmtje(a)yahoo.com> wrote: >> >>>On a sunny day (20 Dec 2008 10:06:18 GMT) it happened Jasen Betts >>><jasen(a)xnet.co.nz> wrote in <giig2q$kmd$7(a)reversiblemaps.ath.cx>: >>> >>>>On 2008-12-19, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >>>>> On a sunny day (Thu, 18 Dec 2008 18:32:11 -0800) it happened Joerg >>>>><notthisjoergsch(a)removethispacbell.net> wrote in >>>>><TID2l.10279$yr3.2278(a)nlpi068.nbdc.sbc.com>: >>>>> >>>>>>> http://www.hobbyprojects.com/thyristor_triac_and_diac/thyristor_as_a_crowbar.html >>>>>>> >>>>>> >>>>>>Has the author ever heard of a gate trigger voltage? Assume 1.5V for >>>>>>now: Zener 5.1V plus Vgt = 6.6V. Phssst ... crackle ... pop ... *BANG* >>>>>>... there goes the majority of connected logic chips. Many of those >>>>>>won't take anything above 6V. >>>>>> >>>>>>The proper way to do a crowbar is with a TL431. >>>>> >>>>> Crowbars are to protect the LOAD, not the supply, and should be at the OUTPUT. >>>>> In case of a 100K$ load and a 100$ supply, the choice is easy. >>>>> Shorting before the regulator does not guarantee energy in any caps and >>>>> or inductors in the circuit does not make it to the load. >>>>> Simple. >>>> >>>>You can put the crowbar SCR across the input to the regulator and the >>>>over-voltage detector across the output - a kind of feedback. >>>>I suspect that is how Jim designs his. >>> >>>Yes you can do that, and he even showed a small kid diagram with a 7805 IIRC. >>>But that will _not_ protect what happens on the supply line. >>>Jimmy has the typical rightist republican thinking: >>> His method protects his own design, not the load :-) >> >> Jerk, Learn to read. AND: I DIDN'T post any diagram. AND: It DOES >> PROTECT the load... some people here are just TOO STUPID to understand >> simple solutions. > >I suppose it would not protect the load against externally- or load- >generated overvoltages. The "load" generated its own over-voltage ?:-) This thread started as protecting the load from failure of a simple 3.3V linear regulator. Exotic systems would require case-by-case analysis... for example... After the Challenger disaster a complete system-by-system, component-by-component analysis was ordered to determine any possible fault mechanisms. It was yours truly (consulting at Sperry Space, later Honeywell Space) who found the power supply redundancy fault... one supply down, they all go down. It needed a fix that _wasn't_ a complete redesign (requiring all kinds of compliance/qualification testing). So I came up with a fix using HexFETs... all we had to qualify was the HexFET itself (they had no prior "S" rating). So I have the honor of getting the first HexFET into space ;-) == Simple crow-barring of a power supply output, without any well-defined relief/release mechanism seems down-right stupid to me. Citing that everyone is doing it doesn't make it good... it only means it's "cheap" ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | If I'm talking, you should be taking notes.
From: John Devereux on 20 Dec 2008 11:36 Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: > On Sat, 20 Dec 2008 15:49:59 +0000, John Devereux > <john(a)devereux.me.uk> wrote: > >>Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: >> [...] >>> Jerk, Learn to read. AND: I DIDN'T post any diagram. AND: It DOES >>> PROTECT the load... some people here are just TOO STUPID to understand >>> simple solutions. >> >>I suppose it would not protect the load against externally- or load- >>generated overvoltages. > > The "load" generated its own over-voltage ?:-) Sure, I was thinking of something like a motor controller, or perhaps JL's NMR machine. > This thread started as protecting the load from failure of a simple > 3.3V linear regulator. > > Exotic systems would require case-by-case analysis... for example... > > After the Challenger disaster a complete system-by-system, > component-by-component analysis was ordered to determine any possible > fault mechanisms. > > It was yours truly (consulting at Sperry Space, later Honeywell Space) > who found the power supply redundancy fault... one supply down, they > all go down. > > It needed a fix that _wasn't_ a complete redesign (requiring all kinds > of compliance/qualification testing). > > So I came up with a fix using HexFETs... all we had to qualify was the > HexFET itself (they had no prior "S" rating). > > So I have the honor of getting the first HexFET into space ;-) Sounds like the "oring controllers" some of the semi manufacturers seem to be peddling. > Simple crow-barring of a power supply output, without any well-defined > relief/release mechanism seems down-right stupid to me. Citing that > everyone is doing it doesn't make it good... it only means it's > "cheap" ;-) No argument here. -- John Devereux
From: Jan Panteltje on 20 Dec 2008 12:06 On a sunny day (Sat, 20 Dec 2008 15:49:59 +0000) it happened John Devereux <john(a)devereux.me.uk> wrote in <87prjmj17c.fsf(a)cordelia.devereux.me.uk>: >I suppose it would not protect the load against externally- or load- >generated overvoltages. This is exactly one of the important points. I know at least about one case where a guy connected the 24 V PLC power to the 5 V logic. If you have a crowbar at the output, passively measuring the output (thyristor + zener), then you have a better chance of keeping the replacement cost low. In this case they had to order new boards for a huge amount of money. There are many ways, with a probability much higher then a series regulator failing, how a high voltage can land on a low voltage line, circuit failures in other electronics that use both supplies could happen too. The 'evidence' case the republican Tommy refers to, does not hold if for example 24 V is applied to the output of a 3.3V regulator with crowbar before the regulator, as it may destroy the regulator anyways. Anyways, just short the output, there may even be fold back still working, I have seen drifting supplies too, bit high voltage, crowbar active. The old Philips K9 chassis had a crowbar in the series switcher 160V (IIRC) output, to protect the horizontal output and every other thing in the set getting supply from that. It has a primary fuse too, but those switch mode would just go tick tick tick if the transistors were not kaput. Protect the load.
From: Joerg on 20 Dec 2008 12:22
Jim Thompson wrote: [...] > > Simple crow-barring of a power supply output, without any well-defined > relief/release mechanism seems down-right stupid to me. ... The relief/release mechanism _has_ been shown in this thread. There is: a. Primary fuse b. Current sense resistor c. Transformer thermofuse Of course, all (not just one alone) need to be calculated, tested and qualified to do a graceful job, meaning no loud bang or serious plume of smoke or whatever else the client requires. The goal must be that only the primary fuse goes as that is panel accessible by field service folks. They often aren't allowed or equipped to open unit panels and dive into the circuit board level. > ... Citing that > everyone is doing it doesn't make it good... it only means it's > "cheap" ;-) > Nope. If all the major manufacturers do it one should at least consider it and find out why they do it that way. I know for a fact that they also cater hi-rel markets. Just one more reason although I am sure your opinion is cast in concrete here: If a sense line is shorted or one of the supply lines comes loose a bit for some reason the supply will think it needs to shovel some more coals ... crowbar comes. Both your crowbar and mine will tackle that. But in my case the field service guy can just re-affix the wires and swap a panel fuse. In your case the power supply box must be opened. This is mostly not desired and field personnel is often not allowed to do that -> PSU swap -> send back -> $$$ Aside from the fact that high-amperage fuses in DC paths are very frowned upon by agency compliance guys and by me (arcing). -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |