Jim Thompson wrote:> On Sun, 02 Dec 2012 00:53:21 -0500, legg <legg@nospam.magma.ca> wrote: > >> On Sat, 01 Dec 2012 16:49:06 -0800, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Jim Thompson wrote: >>>> On Sat, 01 Dec 2012 15:49:26 -0800, Joerg <invalid@invalid.invalid> >>>> wrote: >>>> >>>>> Jim Thompson wrote: >>>>>> On Sat, 01 Dec 2012 13:35:06 -0800, Joerg <invalid@invalid.invalid> >>>>>> wrote: >>>>>> >>>>>>> Fred Abse wrote: >>>>>>>> On Fri, 30 Nov 2012 14:17:47 -0800, Joerg wrote: >>>>>>>> >>>>>>>>> #3 is the only option I ever consider. Personally I like to have the SCR >>>>>>>>> right at the circuit side of the fuse. If the fuse were at the input and >>>>>>>>> the SCR were at the output you'd have the upper FET and the inductor in >>>>>>>>> the path. This will slow down the fuse tripping and there is a chance that >>>>>>>>> the FET grenades before the fuse trips, something that is generally not >>>>>>>>> desired. >>>>>>>> Seconded. >>>>>>>> >>>>>>> Hey, we have the absolute majority in the house now :-) >>>>>> Sounds like a couple of amateurs when it comes to computing I^2*t >:-} >>>>>> >>>>> Huh? >>>>> >>>>> This works, and fast, done it many times. One has to make sure that the >>>>> SCR triggers with gusto and is big enough. >>>> I misconscrewed you as the one saying "inductor"... or maybe not >:-} >>>> >>> That was my point, ideally you don't want to have the inductor in the path. >> Presence of the inductor will not reduce the effectiveness of ovp >> crowbar protection that is located on the output terminals. Neither >> will a grenading fet. >> >> RL > > Presence of an inductor slows the rise of current in the fuse AND the > SCR, adding more risk to the I^2*t margin. >But the *PHUT* sound will be more pronounced :-) -- Regards, Joerg http://www.analogconsultants.com/
Over Voltage Protection Crowbar Circuit
Started by ●November 30, 2012
Reply by ●December 2, 20122012-12-02
Reply by ●December 2, 20122012-12-02
On Sun, 02 Dec 2012 08:49:16 -0800, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>The way to tell the difference is to put current into it for a while, then see >if the car starts. Thses electronic chargers are smart enought to current and >voltage limit. They are even smarter, in that they refuse to make any current >below some terminal voltage. That sells more batteries.I'm not so sure about the Exide brand chargers sold by Kragen. One of the battery chargers in my picture tried to charge a battery with a shorted cell and cause the electrolyte to eventually boil. Just about everything in the radio vault had some form of corrosion damage. Maybe the newer variety of battery charger has a circuit to detect terminal voltage and refuse to charge anything below 10.5VDC or such.>>>I had a zero volt battery, some light left on for a weekend or something. I went >>>to Kragen Auto Parts and bought a charger, and it wouldn't even try. Zero output >>>measured current. I took it back and they said the battery was destroyed and >>>that I needed a new one. >> >>Then the battery charger controller did it's job. It protected itself >>from a potential hazard. > >What hazard? Current limiting?The battery that boiled the electrolyte was probably not hot enough to start a fire. Spraying hot acid all over the wall didn't do much for the unistrut, coax cables, and connectors on the wall. I could have sued Kragen or Exide for not providing adequate protection on their chargers. It's possible that someone did sue, resulting in a redesign that would prevent any furthur such incidents. (I know, I'm guessing). That might explain why it refused to charge your totally dead battery.>Its job is to sell suckers new batteries.Yeah, I guess that's the net effect, but that probably wasn't the intent. A trickle charge, until the terminal voltage increased, would have solved the problem, but that's apparently not a feature of the low end chargers. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Reply by ●December 2, 20122012-12-02
On Friday, November 30, 2012 4:17:59 PM UTC-5, panfilero wrote: You need a combination of everything. Ckt below is based on data for 5A Fast Blo http://www1.cooperbussmann.com/pdf/6d98543c-8f41-4e37-9ba5-0349eff27a02.pdf and will clear ciruit in 10ms maximum. Check your blocking diode surge ratings. Please view in a fixed-width font such as Courier. . . . SD . .------|<|-------------. . | | . FUSE | -------- + | . 100VDC>--/\/\-----+---+----+-|>|->>| 24VDC |-->>-+----->> TO LOAD . 5A F | | | | | . | | | SUPPLY| | . | R | -------- | . | [1R] | | . | | - - | . C | | /// | . +| | | . 7500uF === | | . -| | __ ------- . | |A _| TRIG| OVP | . | --- ---+----------------| DETECT| . | \ //G | | CKT | . | --- | ------- . | |K [470] | . | | | | . >----------+---+------+--------------------+-----> . | | . --- GND --- . /// /// . . . 2 . AMP SECONDS CALC: . . | . | . IPK| * . | * * . | * * . | * * . | * . | * * . | * * . | . ----+------------------------- . | . TIME -> . . . . T 2 . / 2 IPK . E = | (IPK exp(-t/RC)) dt= --- RC (1- exp(-2T/RC)) . / 2 . 0 . . T usually taken to be 50% current amplitude point T50 . . T50= RC LN(2) . . T50 must exceed fuse rated maximum melt time at IPK . which is 10ms for F-rated fuse . . 2 . IPK 2 . E = --- RC X 0.75 or C= 2 x E /(IPK x R x 0.75) . 2 . . Using Bussman TR1/MCRW5A Fast Blow with 300A interrupting . . rating at 125 VDC, E= 3 A^2 x s . . . Then select R= 1R so IPK is 50A minimum with allowance for other . . limiting effects such as ESR of C of addional 1R. . . . 2 . making C the larger of C= 2x3/(50 x 2 x 0.75)= 1600uF . . . and T50/(RLN(2))= 10ms/(2 x 0.7)= 7500uF . .
Reply by ●December 2, 20122012-12-02
On Saturday, December 1, 2012 12:23:11 AM UTC-8, upsid...@downunder.com wrote:> On Fri, 30 Nov 2012 15:50:55 -0600, Jon Elson <jmelson@wustl.edu> > wrote:> >Yup, a well-sized SCR is probably the best at producing a low-drop short > >when called upon, and surviving the event.> Please remember to put some ferrites in series with the SCR gate > drive.Maybe not in the gate, but at the anode? SCRs have a dI/dt limit to be observed, and this a capacitor-being-discharged event. It'd be a shame to blow both the fuse and the protective SCR in each event (but the SCR is likely to fail short, which is at least safe). Some surge protect schemes expend fuse and SCR together.
Reply by ●December 2, 20122012-12-02
On Friday, November 30, 2012 4:17:59 PM UTC-5, panfilero wrote:> I'm needing an over-voltage protection circuit to put at the output of a switching regulator that takes in 100V input and drops it to 24V... I'd like to protect the output from going over 28V. > > > > Here's the 3 options I was considering: For all the options the point is to blow my 5A fast acting fuse that's at the input, so I'm trying to decide on a way to short my output > > > > 1. A Zener - I'm thinking these get rather bulky for higher current handling, and they're not very accurate > > > > 2. A TVS - Probably better than the Zener option as far as current handling and bulkiness... I think TVS kills Zener for this application > > > > 3. An SCR - I could trigger an SCR off of a LM431 to get an accurate trip voltage and I think I could probably find a decently sized SCR that could handle the current required to make the fuse pop > > > > Anybody have any thoughts or recommendations for OVP circuits like this... I'm likeing the SCR option right now > > > > much thanks!Would help to discharge the C thru the fuse: Please view in a fixed-width font such as Courier. . . . SD . .------|<|-------------. . | | . FUSE | -------- + | . 100VDC>----+---/\/\---+----+-|>|->>| 24VDC |-->>-+----->> TO LOAD . | 5A F | | | | . | | | SUPPLY| | . | R | -------- | . | [1R] | | . | | - - | . C | | /// | . +| | | . 7500uF === | | . -| | __ ------- . | |A _| TRIG| OVP | . | --- ---+----------------| DETECT| . | \ //G | | CKT | . | --- | ------- . | |K [470] | . | | | | . >---+------+---+------+--------------------+-----> . | | . --- GND --- . /// /// . . . 2 . AMP SECONDS CALC: . . | . | . IPK| * . | * * . | * * . | * * . | * . | * * . | * * . | . ----+------------------------- . | . TIME -> . . . . T 2 . / 2 IPK . E = | (IPK exp(-t/RC)) dt= --- RC (1- exp(-2T/RC)) . / 2 . 0 . . T usually taken to be 50% current amplitude point T50 . . T50= RC LN(2) . . T50 must exceed fuse rated maximum melt time at IPK . which is 10ms for F-rated fuse . . 2 . IPK 2 . E = --- RC X 0.75 or C= 2 x E /(IPK x R x 0.75) . 2 . . Using Bussman TR1/MCRW5A Fast Blow with 300A interrupting . . rating at 125 VDC, E= 3 A^2 x s . . . Then select R= 1R so IPK is 50A minimum with allowance for other . . limiting effects such as ESR of C of addional 1R. . . . 2 . making C the larger of C= 2x3/(50 x 2 x 0.75)= 1500uF . . . and T50/(RLN(2))= 10ms/(2 x 0.7)= 7500uF . . .
Reply by ●December 2, 20122012-12-02
On a sunny day (Sun, 2 Dec 2012 10:33:46 -0800 (PST)) it happened bloggs.fredbloggs.fred@gmail.com wrote in <37c61395-3021-46f4-b926-608edddbf158@googlegroups.com>:>On Friday, November 30, 2012 4:17:59 PM UTC-5, panfilero wrote: > >You need a combination of everything. Ckt below is based on data for 5A Fast Blo >http://www1.cooperbussmann.com/pdf/6d98543c-8f41-4e37-9ba5-0349eff27a02.pdf and will clear ciruit in 10ms maximum. Check your blocking diode surge ratings. > > Please view in a fixed-width font such as Courier. > >. >. >. SD >. .------|<|-------------. >. | | >. FUSE | -------- + | >. 100VDC>--/\/\-----+---+----+-|>|->>| 24VDC |-->>-+----->> TO LOAD >. 5A F | | | | | >. | | | SUPPLY| | >. | R | -------- | >. | [1R] | | >. | | - - | >. C | | /// | >. +| | | >. 7500uF === | | >. -| | __ ------- >. | |A _| TRIG| OVP | >. | --- ---+----------------| DETECT| >. | \ //G | | CKT | >. | --- | ------- >. | |K [470] | >. | | | | >. >----------+---+------+--------------------+-----> >. | | >. --- GND --- >. /// /// >. >. >. 2 >. AMP SECONDS CALC: >. >. | >. | >. IPK| * >. | * * >. | * * >. | * * >. | * >. | * * >. | * * >. | >. ----+------------------------- >. | >. TIME -> >. >. >. >. T 2 >. / 2 IPK >. E = | (IPK exp(-t/RC)) dt= --- RC (1- exp(-2T/RC)) >. / 2 >. 0 >. >. T usually taken to be 50% current amplitude point T50 >. >. T50= RC LN(2) >. >. T50 must exceed fuse rated maximum melt time at IPK >. which is 10ms for F-rated fuse >. >. 2 >. IPK 2 >. E = --- RC X 0.75 or C= 2 x E /(IPK x R x 0.75) >. 2 >. >. Using Bussman TR1/MCRW5A Fast Blow with 300A interrupting >. >. rating at 125 VDC, E= 3 A^2 x s >. >. >. Then select R= 1R so IPK is 50A minimum with allowance for other >. >. limiting effects such as ESR of C of addional 1R. >. >. >. 2 >. making C the larger of C= 2x3/(50 x 2 x 0.75)= 1600uF >. >. >. and T50/(RLN(2))= 10ms/(2 x 0.7)= 7500uF >Nice
Reply by ●December 2, 20122012-12-02
On Sunday, December 2, 2012 1:45:51 PM UTC-5, Jan Panteltje wrote:> On a sunny day (Sun, 2 Dec 2012 10:33:46 -0800 (PST)) it happened > > bloggs.fredbloggs.fred@gmail.com wrote in > > <37c61395-3021-46f4-b926-608edddbf158@googlegroups.com>: > > > > >On Friday, November 30, 2012 4:17:59 PM UTC-5, panfilero wrote: > > > > > >You need a combination of everything. Ckt below is based on data for 5A Fast Blo > > >http://www1.cooperbussmann.com/pdf/6d98543c-8f41-4e37-9ba5-0349eff27a02.pdf and will clear ciruit in 10ms maximum. Check your blocking diode surge ratings. > > > > > > Please view in a fixed-width font such as Courier. > > > > > >. > > >. > > >. SD > > >. .------|<|-------------. > > >. | | > > >. FUSE | -------- + | > > >. 100VDC>--/\/\-----+---+----+-|>|->>| 24VDC |-->>-+----->> TO LOAD > > >. 5A F | | | | | > > >. | | | SUPPLY| | > > >. | R | -------- | > > >. | [1R] | | > > >. | | - - | > > >. C | | /// | > > >. +| | | > > >. 7500uF === | | > > >. -| | __ ------- > > >. | |A _| TRIG| OVP | > > >. | --- ---+----------------| DETECT| > > >. | \ //G | | CKT | > > >. | --- | ------- > > >. | |K [470] | > > >. | | | | > > >. >----------+---+------+--------------------+-----> > > >. | | > > >. --- GND --- > > >. /// /// > > >. > > >. > > >. 2 > > >. AMP SECONDS CALC: > > >. > > >. | > > >. | > > >. IPK| * > > >. | * * > > >. | * * > > >. | * * > > >. | * > > >. | * * > > >. | * * > > >. | > > >. ----+------------------------- > > >. | > > >. TIME -> > > >. > > >. > > >. > > >. T 2 > > >. / 2 IPK > > >. E = | (IPK exp(-t/RC)) dt= --- RC (1- exp(-2T/RC)) > > >. / 2 > > >. 0 > > >. > > >. T usually taken to be 50% current amplitude point T50 > > >. > > >. T50= RC LN(2) > > >. > > >. T50 must exceed fuse rated maximum melt time at IPK > > >. which is 10ms for F-rated fuse > > >. > > >. 2 > > >. IPK 2 > > >. E = --- RC X 0.75 or C= 2 x E /(IPK x R x 0.75) > > >. 2 > > >. > > >. Using Bussman TR1/MCRW5A Fast Blow with 300A interrupting > > >. > > >. rating at 125 VDC, E= 3 A^2 x s > > >. > > >. > > >. Then select R= 1R so IPK is 50A minimum with allowance for other > > >. > > >. limiting effects such as ESR of C of addional 1R. > > >. > > >. > > >. 2 > > >. making C the larger of C= 2x3/(50 x 2 x 0.75)= 1600uF > > >. > > >. > > >. and T50/(RLN(2))= 10ms/(2 x 0.7)= 7500uF > > > > > > > NiceI deleted that post on Google- see follow-up with capacitor on other side of fuse - <smacks self in head >
Reply by ●December 2, 20122012-12-02
On 12/2/2012 8:42 AM, legg wrote:> > OVP thresholds of the crude cowbar circuit are set higher than the > circuit function can normally achieve. This would be a voltage higher > than any battery you might attempt to charge with this normal output.> RLYou're exhibiting symptoms of the pervasive disease I seek to eradicate/prevent. It's known by various names... Tunnel vision. Not invented here. I'm too smart for my own good syndrome. Pervasive incompetence. Infected engineers get defensive and tell you why you're wrong according to their limited view of the COMPONENT. The guys you want doing your design reviews listen to what's being said in SYSTEM context and figure out how broadening their view might make their designs better. They look for learning opportunities, not arguments. Power supplies are frequently subjected to conditions not spelled out in the spec. The spec may not say much about AC line transients. Inexperienced engineers may not pay attention to that at all. Same for load transients. Pick a power supply. Grab the schematic and the designer. Ask, "what happens at this node when I rip the line cord out of the wall?" Most won't have even considered the possibility. I'm not saying that it's hard to design a crowbar circuit that doesn't have the problem. I'm saying that, if you're not paying attention, it's easy to let a bad design get through. Crowbar misbehavior is not an isolated case as evidenced by other inputs to this thread. You'll recall that I asked a question about the application. For a dedicated application, a less-than-optimal crowbar may not be an issue. Here's the backstory that gets me so excited about power supplies. I inherited a hardware group designing a computer workstation. One component was a custom power supply designed by a local power supply house. We'd seen prototypes. Our engineer went down the spec sheet running tests and signed off on the design. But when they got put into computers, we had random failures. The design firm denied responsibility because our engineer couldn't reproduce the symptom. This went on for months. I finally gave up an took one home over the weekend. I returned on Monday with a test fixture. I invited the designer and his boss in for a demo. They brought their latest revision. I put a current probe on the transformer primary and a transient load synchronized to the switcher. By moving the load transient across the timing cycle, I could change the duty factor off 50% and walk the drain current right up the saturation curve. I gave 'em safety glasses and asked them to put their fingers in their ears as I embedded pieces of FET in the ceiling. I then asked how many more they wanted me to destroy before they got the message. The problem wasn't on the spec sheet. The problem wasn't on the schematic. It was on the layout. After all that, they still couldn't get it right. I expect that if I'd suggested here that someone build a current transient tester capable of 10 amps in 10ns, I'd have been told I was an idiot. All I can say is that it's often quicker, easier, cheaper to run the test than to argue why it won't work. But I digress... Back to the story. Purchasing fired 'em and contracted with a firm 500 miles away. Long story short, the first look at the new schematic showed it to be identical to the old schematic. I asked a few questions and discovered that the new firm didn't have the manpower for our design, so they hired someone. And who did they hire but the guy who was laid off from the first local firm. Didn't see that coming. I threw a hissy-fit, so they hired a consultant "fixer" to clean it up. I met with the guy. Took me 15 minutes to decide that he exuded competence. The new design came in on schedule, on budget, it worked and it flew through EMC testing with margin to spare. The design was almost identical to the first one. But it was executed by someone competent and paying attention to the system details. I wanted to hire him, but he wouldn't work that cheap. ;-) Good times...
Reply by ●December 2, 20122012-12-02
On Sun, 02 Dec 2012 11:01:12 -0800, mike <ham789@netzero.net> wrote:>On 12/2/2012 8:42 AM, legg wrote: > >> >> OVP thresholds of the crude cowbar circuit are set higher than the >> circuit function can normally achieve. This would be a voltage higher >> than any battery you might attempt to charge with this normal output. > >> RL > >You're exhibiting symptoms of the pervasive disease I seek to >eradicate/prevent. >It's known by various names... >Tunnel vision. >Not invented here. >I'm too smart for my own good syndrome. >Pervasive incompetence. > >Infected engineers get defensive and tell you why you're wrong >according to their limited view of the COMPONENT. > >The guys you want doing your design reviews listen to what's being >said in SYSTEM context and figure out how broadening their >view might make their >designs better. They look for learning opportunities, not arguments. > >Power supplies are frequently subjected to conditions not >spelled out in the spec. >The spec may not say much about AC line transients. Inexperienced >engineers may not pay attention to that at all. Same for load transients. > >Pick a power supply. Grab the schematic and the designer. >Ask, "what happens at this node when I rip the line cord out of the wall?" >Most won't have even considered the possibility. > >I'm not saying that it's hard to design a crowbar circuit that >doesn't have the problem. I'm saying that, if you're not >paying attention, it's easy to let a bad design get through. >Crowbar misbehavior is not an isolated case as evidenced by other >inputs to this thread. > >You'll recall that I asked a question about the application. >For a dedicated application, a less-than-optimal crowbar may not be >an issue. > >Here's the backstory that gets me so excited about power supplies. > >I inherited a hardware group designing a computer workstation. >One component was a custom power supply designed by a local >power supply house. >We'd seen prototypes. >Our engineer went down the spec sheet running tests and signed >off on the design. >But when they got put into computers, we had random failures. >The design firm denied responsibility because our engineer >couldn't reproduce the symptom. This went on for months. > >I finally gave up an took one home over the weekend. >I returned on Monday with a test fixture. >I invited the designer and his boss in for a demo. >They brought their latest revision. >I put a current probe on the transformer primary >and a transient load synchronized to the switcher. >By moving the load transient across the timing cycle, I could >change the duty factor off 50% and walk the drain current >right up the saturation curve. >I gave 'em safety glasses and asked them to put their fingers >in their ears as I embedded pieces of FET in the ceiling. >I then asked how many more they wanted me to destroy before they >got the message. >The problem wasn't on the spec sheet. >The problem wasn't on the schematic. >It was on the layout. >After all that, they still couldn't get it right. > >I expect that if I'd suggested here that someone build >a current transient tester capable of 10 amps in 10ns, I'd have >been told I was an idiot.We've hacked home-made current transformers that let us measure 50 amp pulses, with risetimes of a couple ns. It's not hard. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●December 2, 20122012-12-02
On Sun, 02 Dec 2012 09:57:51 -0800, Joerg <invalid@invalid.invalid> wrote:>Jim Thompson wrote: >> On Sun, 02 Dec 2012 00:53:21 -0500, legg <legg@nospam.magma.ca> wrote: >> >>> On Sat, 01 Dec 2012 16:49:06 -0800, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> Jim Thompson wrote: >>>>> On Sat, 01 Dec 2012 15:49:26 -0800, Joerg <invalid@invalid.invalid> >>>>> wrote: >>>>> >>>>>> Jim Thompson wrote: >>>>>>> On Sat, 01 Dec 2012 13:35:06 -0800, Joerg <invalid@invalid.invalid> >>>>>>> wrote: >>>>>>> >>>>>>>> Fred Abse wrote: >>>>>>>>> On Fri, 30 Nov 2012 14:17:47 -0800, Joerg wrote: >>>>>>>>> >>>>>>>>>> #3 is the only option I ever consider. Personally I like to have the SCR >>>>>>>>>> right at the circuit side of the fuse. If the fuse were at the input and >>>>>>>>>> the SCR were at the output you'd have the upper FET and the inductor in >>>>>>>>>> the path. This will slow down the fuse tripping and there is a chance that >>>>>>>>>> the FET grenades before the fuse trips, something that is generally not >>>>>>>>>> desired. >>>>>>>>> Seconded. >>>>>>>>> >>>>>>>> Hey, we have the absolute majority in the house now :-) >>>>>>> Sounds like a couple of amateurs when it comes to computing I^2*t >:-} >>>>>>> >>>>>> Huh? >>>>>> >>>>>> This works, and fast, done it many times. One has to make sure that the >>>>>> SCR triggers with gusto and is big enough. >>>>> I misconscrewed you as the one saying "inductor"... or maybe not >:-} >>>>> >>>> That was my point, ideally you don't want to have the inductor in the path. >>> Presence of the inductor will not reduce the effectiveness of ovp >>> crowbar protection that is located on the output terminals. Neither >>> will a grenading fet. >>> >>> RL >> >> Presence of an inductor slows the rise of current in the fuse AND the >> SCR, adding more risk to the I^2*t margin. >> > >But the *PHUT* sound will be more pronounced :-)<SMIRK :-> ...Jim Thompson -- | James E.Thompson, CTO | 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.
