Big crowbar module for <4VDC?
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From: Jim Thompson on 18 Dec 2008 19:46 On Thu, 18 Dec 2008 16:10:36 -0800 (PST), Tim Williams <tmoranwms(a)gmail.com> wrote: >On Dec 17, 7:12 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- >Web-Site.com> wrote: >> Second question. You _are_ aware that the crowbar goes on the _input_ >> side of the linear regulator, aren't you ?:-) > >Hey Jim, you respect AoE2 last I heard, right? Why, then, do they >also recommend putting the crowbar at the output? Which is, >incidentially, the logical place to put it when you want to protect >$10k equipment powered by said supply anyway. Equipment >> supply, >protect equipment. QED. > >Tim Where did you hear that I respected AoE? It's nothing more than a compendium of circuits... somewhat on a par with Ideas for Design, are they not? Crowbar on input side of a linear regulator is ideal for speed and efficacy of fuse blowing. Crowbar on the output side is a prayer... hope it can sink more current than the faulty regulator can deliver, and that the resultant heating won't violate the various regulatory rules that Joerg worries more about than good engineering practice... when that melts, then there's the spike that takes out $BIG load anyway ;-) But I suppose there _are_ people who fret over spending $1 to protect $BIG load <smirk> ...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 | I love to cook with wine Sometimes I even put it in the food
From: Jim Thompson on 18 Dec 2008 19:58 On Thu, 18 Dec 2008 16:10:36 -0800 (PST), Tim Williams <tmoranwms(a)gmail.com> wrote: >On Dec 17, 7:12 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- >Web-Site.com> wrote: >> Second question. You _are_ aware that the crowbar goes on the _input_ >> side of the linear regulator, aren't you ?:-) > >Hey Jim, you respect AoE2 last I heard, right? Why, then, do they >also recommend putting the crowbar at the output? Which is, >incidentially, the logical place to put it when you want to protect >$10k equipment powered by said supply anyway. Equipment >> supply, >protect equipment. QED. > >Tim Pardon my quoting Maxim ;-)... http://www.maxim-ic.com/glossary/index.cfm/Ac/V/ID/1039/Tm/crowbar or Hobby Projects http://www.hobbyprojects.com/thyristor_triac_and_diac/thyristor_as_a_crowbar.html or Fairchild http://74.125.95.132/search?q=cache:yk_Mxz8_OisJ:www.fairchildsemi.com/an/AB/AB-17.pdf+%22crowbar+circuit%22&hl=en&ct=clnk&cd=11&gl=us (back into the PDF) For switchers I tend toward redundancy which can be guaranteed to take out the appropriate failure paths... but this designing, unlike that for linear supplies, must be on a case-by-case basis. ...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 | I love to cook with wine Sometimes I even put it in the food
From: Jim Thompson on 18 Dec 2008 20:22 On Thu, 18 Dec 2008 17:58:46 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Thu, 18 Dec 2008 16:10:36 -0800 (PST), Tim Williams ><tmoranwms(a)gmail.com> wrote: > >>On Dec 17, 7:12 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- >>Web-Site.com> wrote: >>> Second question. You _are_ aware that the crowbar goes on the _input_ >>> side of the linear regulator, aren't you ?:-) >> >>Hey Jim, you respect AoE2 last I heard, right? Why, then, do they >>also recommend putting the crowbar at the output? Which is, >>incidentially, the logical place to put it when you want to protect >>$10k equipment powered by said supply anyway. Equipment >> supply, >>protect equipment. QED. >> >>Tim > >Pardon my quoting Maxim ;-)... > >http://www.maxim-ic.com/glossary/index.cfm/Ac/V/ID/1039/Tm/crowbar > >or Hobby Projects > >http://www.hobbyprojects.com/thyristor_triac_and_diac/thyristor_as_a_crowbar.html > >or Fairchild > >http://74.125.95.132/search?q=cache:yk_Mxz8_OisJ:www.fairchildsemi.com/an/AB/AB-17.pdf+%22crowbar+circuit%22&hl=en&ct=clnk&cd=11&gl=us > >(back into the PDF) > >For switchers I tend toward redundancy which can be guaranteed to take >out the appropriate failure paths... but this designing, unlike that >for linear supplies, must be on a case-by-case basis. > > ...Jim Thompson And, and... for those that would impugn my systems experience... From 1962-1970 I designed primarily ASIC's for automobile application, wherein I defined the overall system. From 1970-1973 I designed hybrid SYSTEMS for (primarily) military application. From 1973-1987 I was about 50% discrete systems / 50% ASIC's. From 1987 to present I'm mostly doing ASIC's with an occasional system design, but even with the ASIC's I dominate making the whole system play as desired... _never_ trust a system architect... every time I do they "f-bomb" something up ;-) ...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 | I love to cook with wine Sometimes I even put it in the food
From: legg on 18 Dec 2008 21:15 On Thu, 18 Dec 2008 17:46:38 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Thu, 18 Dec 2008 16:10:36 -0800 (PST), Tim Williams ><tmoranwms(a)gmail.com> wrote: > >>On Dec 17, 7:12�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- >>Web-Site.com> wrote: >>> Second question. �You _are_ aware that the crowbar goes on the _input_ >>> side of the linear regulator, aren't you ?:-) >> >>Hey Jim, you respect AoE2 last I heard, right? Why, then, do they >>also recommend putting the crowbar at the output? Which is, >>incidentially, the logical place to put it when you want to protect >>$10k equipment powered by said supply anyway. Equipment >> supply, >>protect equipment. QED. >> >>Tim > >Where did you hear that I respected AoE? > >It's nothing more than a compendium of circuits... somewhat on a par >with Ideas for Design, are they not? > >Crowbar on input side of a linear regulator is ideal for speed and >efficacy of fuse blowing. > >Crowbar on the output side is a prayer... hope it can sink more >current than the faulty regulator can deliver, and that the resultant >heating won't violate the various regulatory rules that Joerg worries >more about than good engineering practice... when that melts, then >there's the spike that takes out $BIG load anyway ;-) > >But I suppose there _are_ people who fret over spending $1 to protect >$BIG load <smirk> > > ...Jim Thompson The suitability will depend on the application circuit - and access in the application. Location and method will vary. Add-on modules assume no internal access, save the supply output terminals. For linears with built-in crowbar circuitry, blowing the primary fuse from the regulator input is traditionally the safer and more predictable method. At lower voltages, higher currents and under more complex load conditions, other methods might make more sense, considering advances in power mosfet technology and integrated power supervisory bells and whistles. RL
From: Joerg on 18 Dec 2008 21:19
Jim Thompson wrote: > On Thu, 18 Dec 2008 15:39:20 -0800, Joerg > <notthisjoergsch(a)removethispacbell.net> wrote: > >> Jim Thompson wrote: >>> On Thu, 18 Dec 2008 13:40:56 -0800, Joerg >>> <notthisjoergsch(a)removethispacbell.net> wrote: >>> >>>> Jim Thompson wrote: >>>>> On Thu, 18 Dec 2008 12:48:54 -0800, Joerg >>>>> <notthisjoergsch(a)removethispacbell.net> wrote: >>>>> >>>>>> Jim Thompson wrote: >>>>>>> On Thu, 18 Dec 2008 11:16:38 -0800, Joerg >>>>>>> <notthisjoergsch(a)removethispacbell.net> wrote: >>>>>>> >>>> [...] >>>> >>>> >>>>>>>> I have here various schematics of OEM linears from reputable US >>>>>>>> manufacturers (unfortunately not at liberty to post on the web). All >>>>>>>> have the SCR connected to the output rails, just like I always did. Now >>>>>>>> all those manufacturers can't be wrong, can they? >>>>>>> They're probably all Democrats ;-) >>>>>>> >>>>>> I hope none of them read that ;-) >>>>> I guess there's no convincing you that the crowbar goes (properly) >>>>> before the linear, all the energy to blow the fuse (between capacitor >>>>> bank and linear) comes from the capacitor bank, with properly sized >>>>> fuse (fuseI^2*t << scrI^*2t), SCR doesn't even flinch. >>>>> >>>> No, not convinced. Since you don't do system level designs you probably >>>> won't have any: >>> I was doing system level stuff before you were born ;-) >>> >> But that doesn't mean us younger guys couldn't find a more cost >> efficient topology :-)) >> >> Hint: A decent fuse costs quite a bit and fuses always attract the >> scrutiny of the agency compliance inspector. More paperwork, more >> Dollars. And one likes to minimize scrutiny. >> >> >>>> There is a sizeable stash of various linear supplies >>>> here, at the ready when a prototype needs to be lashed up. All from very >>>> reputable manufacturers, in business for decades. _None_ have fuses >>>> between caps and pass devices, and _all_ that are crowbar-equipped have >>>> the crowbar short the output. >>>> >>>> >>>>> I personally consider crow-barring output, with no fuses except >>>>> primary, to be down-right stupid. >>>>> >>>> I consider it the correct method of choice. >>>> >>>> >>>>> But it's not my problem... >>>>> >>>>> My finished designs ALWAYS work ;-) >>>>> >>>> Mine, too. If you have fuses after the caps your crowbar solution is >>>> (probably) going to be ok. >>> That's where they belong. >>> >> I guess this is an area where the two of us will never see eye to eye ... >> >> [...] > > Aha! You don't care what burns up... as long as it's not the $BIG > load ?:-) > No, clients do not care. Whether a regulator loop, a transistor or a transformer failed doesn't matter. The power supply is toast and will be swapped. Of course this is very different on my own designs where power supplies are residing on the same board as the other stuff. Those usually don't get crowbars but FET disconnects. > "...fuses always attract the scrutiny of the agency compliance > inspector..." sounds like a business I don't want to play in. > Then better stay out of med, aero and so on. > Fuses are for safety, n'est ce pas ?:-) > Yes, but only where needed. The fact that they are safety devices is exactly the reason for said scrutiny. I remember a situation where I told a someone umpteen times to replace a resettable thermo-fuse with a simple and cheap non-resettable one. "But then the transformer will be dead" ... "Yes, but else you won't pass med cert in Canada". They kept the resettable version, went to the test lab and promptly ended up with egg in the face. I heard that their Canadian sales reps were very pissed. > And, done properly (aka "my way"), crowbars are _very_ fast at > accomplishing disconnect. > So are mine. Except that the pass devices are toast afterwards. Hey, maybe you should have done an apprenticeship under Earl William Muntz before going to MIT ;-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |