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. -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Over Voltage Protection Crowbar Circuit
Started by ●November 30, 2012
Reply by ●December 1, 20122012-12-01
Reply by ●December 1, 20122012-12-01
On Sat, 01 Dec 2012 10:35:14 -0800, mike wrote:> I wanted to use for charging batteries. Turns out, if you turned off the > power switch before disconnecting the battery, it made a LOT of smoke.Very common. Bench power supplies should *never* be used to charge batteries without a suitably rated diode in series. I've had it done to my bench supplies when I've been away. I better not find out who it was... -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by ●December 1, 20122012-12-01
On Fri, 30 Nov 2012 15:43:05 -0800, John Larkin wrote:> The SCR gate should indeed be driven hard by some schmitt-trigger sort of > thing. A wimpy gate drive (say, a zener from anode to gate) can result in > a slow-spreading current concentration somewhere in the SCR die, and > damage the SCR.Not my experience. A big SCR driven by a sensitive one (like C106) with just an A-G zener is extremely robust. The only faults I've encountered with that sort of circuit (both mine and others') have been age-related false tripping at greater than ten years.> > Moto used to make a specific crowbar driver chip for this application... > can't recall the part number. OnSemi may still make it.I've used them (once). Bitches to keep stable. -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by ●December 1, 20122012-12-01
On Fri, 30 Nov 2012 13:17:59 -0800, 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 outputPut a fuse at the *output* and use the usual SCR/zener circuit. Don't rely on the PSU input fuse. Too uncertain. -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by ●December 1, 20122012-12-01
On Fri, 30 Nov 2012 14:53:09 -0700, Jim Thompson wrote:> Just use the SCR to clear a fuse. Just make sure your PCB traces are up > to the pulse current. I have measured ~100A while clearing a 1A fuse... > makes a teeny little flash when expiring ;-) >I agree. The biggest I've done was for a 100-amp bought-in power supply. I used fabricated copper busbars for that. It made a satisfying thump on test. -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by ●December 1, 20122012-12-01
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 :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●December 1, 20122012-12-01
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 >:-} ...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 1, 20122012-12-01
On Sat, 01 Dec 2012 13:11:35 -0800, Fred Abse <excretatauris@invalid.invalid> wrote:>On Sat, 01 Dec 2012 10:35:14 -0800, mike wrote: > >> I wanted to use for charging batteries. Turns out, if you turned off the >> power switch before disconnecting the battery, it made a LOT of smoke. > >Very common. Bench power supplies should *never* be used to charge >batteries without a suitably rated diode in series. > >I've had it done to my bench supplies when I've been away. I better not >find out who it was...I keep a bench supply at home and up in the cabin, mostly for charging dead car batteries. Most "modern" car battery chargers refuse to put any current into a zero-volt battery, but a bench supply will. I think the car supply places sell the "smart" chargers so that people will think their batteries won't charge, so the auto supply crooks\\\\\ people get to sell people a charger *and* a new battery. I just crank the supply up to 15 or 20 volts, set the current limit (if it has one) to an amp or two, and connect it to the battery overnight. -- 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 1, 20122012-12-01
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. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●December 1, 20122012-12-01
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 >:-} ...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.
