Big crowbar module for <4VDC?
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From: krw on 20 Dec 2008 15:41 In article <oZidnV8jv4oy3dDUnZ2dnUVZ_rbinZ2d(a)earthlink.com>, mike.terrell(a)earthlink.net says... > > Jim Thompson wrote: > > > > 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 ;-) > > > I would rather you had put the first donkey into orbit. A dummy payload? -- Keith
From: Michael A. Terrell on 20 Dec 2008 15:49 krw wrote: > > mike.terrell(a)earthlink.net wrote: > > > > I would rather you had put the first donkey into orbit. > > A dummy payload? A good description, or the first sub orbital load dump. If somebody could really design good audio equipment we could even hear his last pathetic, little girlie screams. The Telemetry equipment designs I worked on passed from DC to 40 MHz at -3dB. ;-) -- http://improve-usenet.org/index.html aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy.
From: krw on 20 Dec 2008 16:02 In article <0aadnYLs3eXJx9DUnZ2dnUVZ_r6dnZ2d(a)earthlink.com>, mike.terrell(a)earthlink.net says... > > krw wrote: > > > > mike.terrell(a)earthlink.net wrote: > > > > > > I would rather you had put the first donkey into orbit. > > > > A dummy payload? > > A good description, or the first sub orbital load dump. SSSSSHHHHHHIIIiiiiiitttt IIIIiinnnnn SSSSSpppppaaaaccceee!! > If somebody could really design good audio equipment we could even hear his > last pathetic, little girlie screams. The Telemetry equipment designs I > worked on passed from DC to 40 MHz at -3dB. ;-) I hope you never passed a dump like the Dumb Donkey. Ow! -- Keith
From: Jim Thompson on 20 Dec 2008 17:19 On Sat, 20 Dec 2008 15:05:25 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: [snip] > >Occurred to me what I _would_ accept: > >Crowbar output of regulator, BUT... > >Use an electronic circuit breaker on the primary to quickly open >circuit it. > >That would alleviate my heartburn over having all that path under >stress until a fuse clears. > > ...Jim Thompson Not very clear was it? I mean for electronic circuit breaker to be triggered by same circuitry that triggered crowbar. ...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: Nico Coesel on 20 Dec 2008 18:12
Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Thu, 18 Dec 2008 09:53:45 -0800, Joerg ><notthisjoergsch(a)removethispacbell.net> wrote: > >>Jim Thompson wrote: >>> On Wed, 17 Dec 2008 15:44:48 -0800, Joerg >>> <notthisjoergsch(a)removethispacbell.net> wrote: >>> >>>> Hello All, >>>> >>>> After modding a 5V linear to 3.3V I feel a bit iffy about the crowbar, >>>> considering the Dollar amount that is going to be connected to it. The >>>> original crowbar is partially under (!) a big electrolytic, a bear to >>>> modify. Plus it probably isn't a good one to begin with, couldn't see a >>>> TL431 in there. >>>> >> >>Ideally yes. Reality, no. Most crowbars are across the output terminals. >>They do their job because typically the supply is toast anyway if the >>crowbar has to kick in. IOW one of the pass transistors has fused shut >>and then it doesn't matter where the crowbar sits. > >Nonsense! Regulator loop fails, pass device can't pass enough current >to blow fuse. > >> >> >>> Short series loop of input electrolytic and fuse and SCR... phzzzzt >>> ;-) >>> >> >>And that's the problem ... the SCR needs to be huge. > >Again nonsense! Sounds like you've never actually designed a >crowbar-protected supply ?? > >I did my first 33 years ago, before simulation capability, worked >perfectly ;-) > >>There is a really >>fat one in the supply (>>TO220) but to get there would require major >>surgery. > >Doesn't take a big "fat one". > >The clue to your learning process is I^2*t From experience: I have an old HP6002A power supply. The previous owner used it to charge a battery. However, he modified to fan to be quiet. So, overtemperature kicks in, crowbar sees Vout > Vset and kicks in as well. Result: traces burned from the PCB but the tiny SCR is still alive. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... "If it doesn't fit, use a bigger hammer!" -------------------------------------------------------------- |