On 12/2/2012 1:26 AM, Jeff Liebermann wrote:> On Sat, 01 Dec 2012 22:14:05 -0800, John Larkin > <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>> A charger is supposed to put current into a battery. > > Sure, but how is it suppose to tell the difference between a depleted > but chargeable battery and a battery with a shorted cell? Without > some manner of ESR measuring algorithm, they look the same to a > commodity charger. The problem is that putting current into a shorted > cell is the same as a room heater.Putting current into a short produces no heat in the short.
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 2 Dec., 09:08, "P E Schoen" <p...@peschoen.com> wrote:> "Jim Thompson" =A0wrote in message > > news:pciib85mttaob0g1ur0frlafu2d98baam8@4ax.com... > > > On Fri, 30 Nov 2012 13:54:33 -0800 (PST), "langw...@fonz.dk" > > <langw...@fonz.dk> wrote: > >> why not something like this: > >>http://www.analog-innovations.com/SED/OverAndReverseVoltageProtection..=.> >> no need for fuses then > > Yep. =A0I always like my own circuits >:-} > > The fuse blower design was done before MOSFET's were common. > > I see some problems with that circuit. The IRLM6401 is only rated at 12V =and> the gate only +/-8V. Of course this is apparently for a low voltage batte=ry,> probably 6V, considering the 3.3 ohm load. M1 seems to be connected so th=at> its internal diode normally conducts, although the 0V biased gate would t=urn> it on. I think there should be a resistor on the gate. The shunt regulato=r> DZ1 is set to 5.2V, so I see this may be for a 5V logic supply. I see tha=t a> voltage over about 5.8V will start to shunt the Vgs of M2 and turn it off > when it becomes less than about 0.6 to 0.95 V gate threshold. But it stil=l> does not seem to provide any voltage regulation to the load, and with 0.0=5> ohms or each MOSET at 1.5A loses 150 mV. If the voltage is only marginall=y> high, or if the load increased, there could be about 2A and 1 or 2 volts =on> the MOSFET which would exceed its power dissipation of 1.3W. > > I don't see what is so great about this circuit. It does not have voltage > regulation or current limiting and it does not have any hysteresis to kee=p> it from entering a destructive linear range or possibly oscillate. The SC=R> crowbar with a fuse (or maybe a polyswitch device) is more robust and far > simpler. > > Maybe you or someone can explain the merits of your circuit. > > Paullook at it as a concept, of course you have to pick fet that can handle the voltage and current and you need something to limit the Vgs if you are running more than ~12V and if you intend to run at marginally high voltage you need something else or make it snap on M1 works as a diode to provide reverse voltage protection if you only need overvoltage you don't need it see it as something that will prevent a supply with the wrong polarity or say 24V instead of 12V from frying stuff -Lasse
Reply by ●December 2, 20122012-12-02
On Sun, 02 Dec 2012 00:36:20 -0800, mike <ham789@netzero.net> wrote:>On 12/1/2012 9:14 PM, legg wrote: >> On Sat, 01 Dec 2012 10:35:14 -0800, mike<ham789@netzero.net> wrote: >><snip>>I used to build test equipment for a living. In many a design review, >I witnessed a circuit that probably met spec, but would have been >a failure in the hands of a typical user. >Hanging a SCR across the output without serious consideration of all >the ways it could get triggered would qualify in that respect. >> >> The crowbar method of protection isn't always used, and it's external >> application in any black box situation should probably be evaluated. >> >> Your battery charging or back-up situation isn't exactly a black box, >> so you should be able to get your mind around it, with a little >> effort. >Again, it's not about me or my application. It's a caution that an SCR >crowbar can be very effective or a ticking time bomb if you're not >paying attention. Designers sometimes don't pay attention.It's just that; with a battery applied, an overvoltage condition is highly unlikely to occurr, due to the clamping action of the battery, itself. A failure in the regulator doesn't result in overvoltage, it results in overcharging. To protect against overcharging due to regulator failure, you'd be counting on the input fuse, as the battery looks just like a high capacity TVS. 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.>> There's no reason why a commercial bench power supply should smoke on >> application of external voltage, within it's normal output compliance, >> save the naivete of it's designer, or the complaisance of it's >> purchaser. >As sentences with no content go, that's a good one. I'd have to agree. >Power supplies are invulnerable unless they aren't.Rephrased - you gets what you pays for, and if you insist on buying crap, then crap ye shall get. RL
Reply by ●December 2, 20122012-12-02
On Sat, 01 Dec 2012 23:26:03 -0800, Jeff Liebermann <jeffl@cruzio.com> wrote:>On Sat, 01 Dec 2012 22:14:05 -0800, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Sat, 01 Dec 2012 21:46:56 -0800, Jeff Liebermann <jeffl@cruzio.com> wrote: > >>><http://802.11junk.com/jeffl/pics/drivel/slides/dead-battery-chargers.html> >(...) > >>>Good conspiracy theory, but I don't think that's the reason. >>>Litigation avoidance seems a better excuse. If there's any >>>possibility of the charger starting a fire, or in any way damaging a >>>customers equipment or facility, the charger should shut down. >> >>A charger is supposed to put current into a battery. > >Sure, but how is it suppose to tell the difference between a depleted >but chargeable battery and a battery with a shorted cell? Without >some manner of ESR measuring algorithm, they look the same to a >commodity charger. The problem is that putting current into a shorted >cell is the same as a room heater.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 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? Its job is to sell suckers new batteries. -- 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 07:50:22 -0600, John S <Sophi.2@invalid.org> wrote:>On 12/2/2012 1:26 AM, Jeff Liebermann wrote: >> On Sat, 01 Dec 2012 22:14:05 -0800, John Larkin >> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>> A charger is supposed to put current into a battery. >> >> Sure, but how is it suppose to tell the difference between a depleted >> but chargeable battery and a battery with a shorted cell? Without >> some manner of ESR measuring algorithm, they look the same to a >> commodity charger. The problem is that putting current into a shorted >> cell is the same as a room heater. > >Putting current into a short produces no heat in the short.I stand corrected. Rephrasing: The problem is that putting current into a battery with a shorted cell is the same as a room heater, causing the good cells to overcharge and overheat. -- 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
legg 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. >A grenading FET or inductor will, however, increase the chance of consequential damage and is thus best avoided. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●December 2, 20122012-12-02
legg wrote:> On Fri, 30 Nov 2012 14:17:47 -0800, Joerg <invalid@invalid.invalid> > wrote: > >> 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! >> >> #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. > > Applying the crowbar to the output is the most effective way of > reducing potential damage to the load - which is it's intended > function. The end user would usually prefer that your power supply > turn itself into rubble, before any harm can come to the load. Best to > test the effectiveness of any protection method, as this has priority. > A grenading fet would only pass single-fault abnormals in an enclosure > (if isolation barriers are not compromised in the process) and is best > avoided by design. >In most of my fields any sort of grenading has serious consequences. Like Federales waltzing in for a throrough investigation. That is not something the user wants to have happen.> In many cases (though not in this simple buck example) the presence of > an isolation barrier will alter design considerations for ovp > protection. >Could be, it depends. Usually on the amount of reservoir capacitance available downstream. If there is a cap downstream that holds enough energy to keep pushing an overvoltage for a while you need to crowwbar there. But then there should also be a fuse at that spot. Creating a dead short across a cap with a big SCR is a bit like Russian roulette. In most cases the iso barrier only means one has to ferry the trigger signal across. This adds cost but sometimes that is well-invested money. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●December 2, 20122012-12-02
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. > >RLPresence of an inductor slows the rise of current in the fuse AND the SCR, adding more risk to the I^2*t margin. ...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.
Reply by ●December 2, 20122012-12-02
On Sun, 2 Dec 2012 03:08:32 -0500, "P E Schoen" <paul@peschoen.com> wrote:>"Jim Thompson" wrote in message >news:pciib85mttaob0g1ur0frlafu2d98baam8@4ax.com... > >> On Fri, 30 Nov 2012 13:54:33 -0800 (PST), "langwadt@fonz.dk" >> <langwadt@fonz.dk> wrote: > >>> why not something like this: >>> http://www.analog-innovations.com/SED/OverAndReverseVoltageProtection.pdf >>> no need for fuses then > >> Yep. I always like my own circuits >:-} > >> The fuse blower design was done before MOSFET's were common. > >I see some problems with that circuit. The IRLM6401 is only rated at 12V and >the gate only +/-8V. Of course this is apparently for a low voltage battery, >probably 6V, considering the 3.3 ohm load. M1 seems to be connected so that >its internal diode normally conducts, although the 0V biased gate would turn >it on. I think there should be a resistor on the gate. The shunt regulator >DZ1 is set to 5.2V, so I see this may be for a 5V logic supply. I see that a >voltage over about 5.8V will start to shunt the Vgs of M2 and turn it off >when it becomes less than about 0.6 to 0.95 V gate threshold. But it still >does not seem to provide any voltage regulation to the load, and with 0.05 >ohms or each MOSET at 1.5A loses 150 mV. If the voltage is only marginally >high, or if the load increased, there could be about 2A and 1 or 2 volts on >the MOSFET which would exceed its power dissipation of 1.3W. > >I don't see what is so great about this circuit. It does not have voltage >regulation or current limiting and it does not have any hysteresis to keep >it from entering a destructive linear range or possibly oscillate. The SCR >crowbar with a fuse (or maybe a polyswitch device) is more robust and far >simpler. > >Maybe you or someone can explain the merits of your circuit. > >PaulPerhaps study it more carefully, and observe the 2nd page. And I did say... "Yep. I always like my own circuits >:-} The fuse blower design was done before MOSFET's were common." Did you miss the fuse blower discussion? ...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.
Reply by ●December 2, 20122012-12-02
On Sun, 02 Dec 2012 10:25:03 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> 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. > > ...Jim ThompsonActually, the I^2t term is agravated by peakiness in the current waveform, for a constant transfer of stored charge. If fusing is the limit, then keeping I^2t stress of the fuse and downstream components within the same ballpark makes coordination more predictable, ensuring that the fuse will blow first. RL
