Electronic circuit design discusions :: Fastest AC Electronic Fuse


	Fastest AC Electronic Fuse This is probably an oldie question on here... I'd like to break the AC "hot" if there's too much AC current. This would be due to a short or ground fault. Or.... Shunting the load to burn a fuse on the AC line would be ok too.. I'm afraid that a fuse maybe too slow to protect the electronics from burn out.. Let's say the electronics I'm protecting cannot withstand 1.5x overcurrent. What's faster than a fuse on a AC line? Details Load: The load on the line is not a transformer and is not inductive. Current draw: 2Amps Line voltage: 240Vrms, 60Hz Surge rate: guessing 45Amps in 1uS Rule: 1/4watt current sense resistor. The load circuit has a power bridge rectifier. Maybe I could modify the bridge with transistors to interrupt the surge current? D from BC On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> wrote: - Hide quoted text - >This is probably an oldie question on here... >I'd like to break the AC "hot" if there's too much AC current. >This would be due to a short or ground fault. >Or.... >Shunting the load to burn a fuse on the AC line would be ok too.. >I'm afraid that a fuse maybe too slow to protect the electronics from >burn out.. >Let's say the electronics I'm protecting cannot withstand 1.5x >overcurrent. >What's faster than a fuse on a AC line? >Details >Load: The load on the line is not a transformer and is not inductive. >Current draw: 2Amps >Line voltage: 240Vrms, 60Hz >Surge rate: guessing 45Amps in 1uS >Rule: 1/4watt current sense resistor. >The load circuit has a power bridge rectifier. >Maybe I could modify the bridge with transistors to interrupt the >surge current? >D from BC Years ago I used an SCR to blow fuses (on the load side). I think it was in the microsecond range. Warning, traces need to be fat, otherwise you blow traces instead of fuses... I had ~100A circulating momentarily to blow a 1 Amp fuse ;-) ...Jim Thompson -- \| James E.Thompson, P.E. \| mens \| \| Analog Innovations, Inc. \| et \| \| Analog/Mixed-Signal ASIC's and Discrete Systems \| manus \| \| Phoenix, Arizona Voice:(480)460-2350 \| \| \| E-mail Address at Website Fax:(480)460-2142 \| Brass Rat \| \| http://www.analog-innovations.com \| 1962 \| America: Land of the Free, Because of the Brave -----------------------------------------------Reply----------------------------------------------- On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> wrote: - Hide quoted text - >This is probably an oldie question on here... >I'd like to break the AC "hot" if there's too much AC current. >This would be due to a short or ground fault. >Or.... >Shunting the load to burn a fuse on the AC line would be ok too.. >I'm afraid that a fuse maybe too slow to protect the electronics from >burn out.. >Let's say the electronics I'm protecting cannot withstand 1.5x >overcurrent. >What's faster than a fuse on a AC line? >Details >Load: The load on the line is not a transformer and is not inductive. >Current draw: 2Amps >Line voltage: 240Vrms, 60Hz >Surge rate: guessing 45Amps in 1uS >Rule: 1/4watt current sense resistor. >The load circuit has a power bridge rectifier. >Maybe I could modify the bridge with transistors to interrupt the >surge current? >D from BC One of our customers recently asked us to do that. He needs, basically, an SSR that also acts as a programmable circuit breaker and a current limiter. He needs to simulate cable faults and switch power circuits without exploding anything. We've been scribbling circuits for days, and it's non-trivial. We just a few minutes ago finished whiteboarding the design of a breadboard pcb so we can test the dynamics. John -----------------------------------------------Reply----------------------------------------------- On Mon, 14 May 2007 16:22:01 GMT, D from BC - Hide quoted text - <myrealaddr@comic.com> wrote: >This is probably an oldie question on here... >I'd like to break the AC "hot" if there's too much AC current. >This would be due to a short or ground fault. >Or.... >Shunting the load to burn a fuse on the AC line would be ok too.. >I'm afraid that a fuse maybe too slow to protect the electronics from >burn out.. >Let's say the electronics I'm protecting cannot withstand 1.5x >overcurrent. >What's faster than a fuse on a AC line? >Details >Load: The load on the line is not a transformer and is not inductive. >Current draw: 2Amps >Line voltage: 240Vrms, 60Hz >Surge rate: guessing 45Amps in 1uS >Rule: 1/4watt current sense resistor. >The load circuit has a power bridge rectifier. >Maybe I could modify the bridge with transistors to interrupt the >surge current? >D from BC --- How fast? -- JF -----------------------------------------------Reply----------------------------------------------- On Mon, 14 May 2007 11:40:08 -0700, the renowned John Larkin - Hide quoted text - <jjlar@highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >wrote: >>This is probably an oldie question on here... >>I'd like to break the AC "hot" if there's too much AC current. >>This would be due to a short or ground fault. >>Or.... >>Shunting the load to burn a fuse on the AC line would be ok too.. >>I'm afraid that a fuse maybe too slow to protect the electronics from >>burn out.. >>Let's say the electronics I'm protecting cannot withstand 1.5x >>overcurrent. >>What's faster than a fuse on a AC line? >>Details >>Load: The load on the line is not a transformer and is not inductive. >>Current draw: 2Amps >>Line voltage: 240Vrms, 60Hz >>Surge rate: guessing 45Amps in 1uS >>Rule: 1/4watt current sense resistor. >>The load circuit has a power bridge rectifier. >>Maybe I could modify the bridge with transistors to interrupt the >>surge current? >>D from BC >One of our customers recently asked us to do that. He needs, >basically, an SSR that also acts as a programmable circuit breaker >and a current limiter. He needs to simulate cable faults and switch >power circuits without exploding anything. We've been scribbling >circuits for days, and it's non-trivial. We just a few minutes ago >finished whiteboarding the design of a breadboard pcb so we can test >the dynamics. >John There's some work already out there on IGBTs re shorts into hundreds of volts. IIRC, it's bad to try to turn it off too fast (or too slow, obviously), plus there are some other subtleties. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" s@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -----------------------------------------------Reply----------------------------------------------- I drew a circuit here http://webpages.charter.net/dawill/Images/Electric_Fuse.gif which someone built, and evidently works quite nicely. Maybe you could change the MOSFET to two back-to-back so they'll handle AC. Which I also had to draw for someone it seems: http://webpages.charter.net/dawill/Images/Antiseries%20MOSFET%20Switc... Alternately, you could put a single FET across the DC terminals of a FWB. Obviously, the +12V supply needs to be floating. It could possibly be provided by a resistor+capacitor and diode from the AC terminals of the thing. Interfacing external control/feedback would probably be best done with optoisolators... Tim -- Deep Fryer: A very philosophical monk. Website @ http://webpages.charter.net/dawill/tmoranwms "D from BC" <myrealaddr@comic.com> wrote in message news:ca0h43tb5s2o0fur04dg0jl9vlif5j172o@4ax.com... - Hide quoted text - > This is probably an oldie question on here... > I'd like to break the AC "hot" if there's too much AC current. > This would be due to a short or ground fault. > Or.... > Shunting the load to burn a fuse on the AC line would be ok too.. > I'm afraid that a fuse maybe too slow to protect the electronics from > burn out.. > Let's say the electronics I'm protecting cannot withstand 1.5x > overcurrent. > What's faster than a fuse on a AC line? > Details > Load: The load on the line is not a transformer and is not inductive. > Current draw: 2Amps > Line voltage: 240Vrms, 60Hz > Surge rate: guessing 45Amps in 1uS > Rule: 1/4watt current sense resistor. > The load circuit has a power bridge rectifier. > Maybe I could modify the bridge with transistors to interrupt the > surge current? > D from BC On Mon, 14 May 2007 09:38:01 -0700, Jim Thompson - Hide quoted text - <To-Email-Use-The-Envelope-I@My-Web-Site.com> wrote: >On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >wrote: >>This is probably an oldie question on here... >>I'd like to break the AC "hot" if there's too much AC current. >>This would be due to a short or ground fault. >>Or.... >>Shunting the load to burn a fuse on the AC line would be ok too.. >>I'm afraid that a fuse maybe too slow to protect the electronics from >>burn out.. >>Let's say the electronics I'm protecting cannot withstand 1.5x >>overcurrent. >>What's faster than a fuse on a AC line? >>Details >>Load: The load on the line is not a transformer and is not inductive. >>Current draw: 2Amps >>Line voltage: 240Vrms, 60Hz >>Surge rate: guessing 45Amps in 1uS >>Rule: 1/4watt current sense resistor. >>The load circuit has a power bridge rectifier. >>Maybe I could modify the bridge with transistors to interrupt the >>surge current? >>D from BC >Years ago I used an SCR to blow fuses (on the load side). I think it >was in the microsecond range. Warning, traces need to be fat, >otherwise you blow traces instead of fuses... I had ~100A circulating >momentarily to blow a 1 Amp fuse ;-) > ...Jim Thompson Wow!...peaking to 100A before blow out..... Scary.... I guess it takes time for the fuse element temp to rise to the melting/vaporize point. D from BC -----------------------------------------------Reply----------------------------------------------- On Mon, 14 May 2007 11:40:08 -0700, John Larkin - Hide quoted text - <jjlar@highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >wrote: >>This is probably an oldie question on here... >>I'd like to break the AC "hot" if there's too much AC current. >>This would be due to a short or ground fault. >>Or.... >>Shunting the load to burn a fuse on the AC line would be ok too.. >>I'm afraid that a fuse maybe too slow to protect the electronics from >>burn out.. >>Let's say the electronics I'm protecting cannot withstand 1.5x >>overcurrent. >>What's faster than a fuse on a AC line? >>Details >>Load: The load on the line is not a transformer and is not inductive. >>Current draw: 2Amps >>Line voltage: 240Vrms, 60Hz >>Surge rate: guessing 45Amps in 1uS >>Rule: 1/4watt current sense resistor. >>The load circuit has a power bridge rectifier. >>Maybe I could modify the bridge with transistors to interrupt the >>surge current? >>D from BC >One of our customers recently asked us to do that. He needs, >basically, an SSR that also acts as a programmable circuit breaker >and a current limiter. He needs to simulate cable faults and switch >power circuits without exploding anything. We've been scribbling >circuits for days, and it's non-trivial. We just a few minutes ago >finished whiteboarding the design of a breadboard pcb so we can test >the dynamics. >John To break a DC circuit, a pass transistor can be used.. Easy... But breaking 240V AC...huhhh.. :( I might look at using a little transformer to sense a current surge and have that fire a shunt circuit until a fuse blows.. D from BC -----------------------------------------------Reply----------------------------------------------- On Mon, 14 May 2007 13:43:15 -0500, John Fields - Hide quoted text - <jfie@austininstruments.com> wrote: >On Mon, 14 May 2007 16:22:01 GMT, D from BC ><myrealaddr@comic.com> wrote: >>This is probably an oldie question on here... >>I'd like to break the AC "hot" if there's too much AC current. >>This would be due to a short or ground fault. >>Or.... >>Shunting the load to burn a fuse on the AC line would be ok too.. >>I'm afraid that a fuse maybe too slow to protect the electronics from >>burn out.. >>Let's say the electronics I'm protecting cannot withstand 1.5x >>overcurrent. >>What's faster than a fuse on a AC line? >>Details >>Load: The load on the line is not a transformer and is not inductive. >>Current draw: 2Amps >>Line voltage: 240Vrms, 60Hz >>Surge rate: guessing 45Amps in 1uS >>Rule: 1/4watt current sense resistor. >>The load circuit has a power bridge rectifier. >>Maybe I could modify the bridge with transistors to interrupt the >>surge current? >>D from BC >--- >How fast? I might have to blow up some stuff to find out. :) I'm just interested in rough ideas for various levels of cut-out speed.. Doesn't matter what cost, complexity or parts count. At the moment, the faster ...the better.. D from BC -----------------------------------------------Reply----------------------------------------------- On Mon, 14 May 2007 17:42:45 -0500, "Tim Williams" - Hide quoted text - <tmoran@charter.net> wrote: >I drew a circuit here >http://webpages.charter.net/dawill/Images/Electric_Fuse.gif >which someone built, and evidently works quite nicely. Maybe you could >change the MOSFET to two back-to-back so they'll handle AC. Which I also >had to draw for someone it seems: >http://webpages.charter.net/dawill/Images/Antiseries%20MOSFET%20Switc... >Alternately, you could put a single FET across the DC terminals of a FWB. >Obviously, the +12V supply needs to be floating. It could possibly be >provided by a resistor+capacitor and diode from the AC terminals of the >thing. Interfacing external control/feedback would probably be best done >with optoisolators... >Tim mmm...makes sense to see transistors to shut down the mosfet.. Op amp current sensing might be considered generally slower.. The cct looks like it has a ~6A trip level.... It's easy when a sense resistor has enough V to bias a transistor. Using a floating circuit to control a push pull pair of mosfets looking interesting.. Thanks.. D from BC -----------------------------------------------Reply----------------------------------------------- On Mon, 14 May 2007 09:38:01 -0700, Jim Thompson - Hide quoted text - <To-Email-Use-The-Envelope-I@My-Web-Site.com> wrote: >On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >wrote: >>This is probably an oldie question on here... >>I'd like to break the AC "hot" if there's too much AC current. >>This would be due to a short or ground fault. >>Or.... >>Shunting the load to burn a fuse on the AC line would be ok too.. >>I'm afraid that a fuse maybe too slow to protect the electronics from >>burn out.. >>Let's say the electronics I'm protecting cannot withstand 1.5x >>overcurrent. >>What's faster than a fuse on a AC line? >>Details >>Load: The load on the line is not a transformer and is not inductive. >>Current draw: 2Amps >>Line voltage: 240Vrms, 60Hz >>Surge rate: guessing 45Amps in 1uS >>Rule: 1/4watt current sense resistor. >>The load circuit has a power bridge rectifier. >>Maybe I could modify the bridge with transistors to interrupt the >>surge current? >>D from BC >Years ago I used an SCR to blow fuses (on the load side). I think it >was in the microsecond range. Warning, traces need to be fat, >otherwise you blow traces instead of fuses... I had ~100A circulating >momentarily to blow a 1 Amp fuse ;-) > ...Jim Thompson I'm wondering what's more explosive... Slowly sneaking up the current through the fuse until it blows... Or..... suddenly connecting the fuse across a 300V charged 100uF low ESR capacitor? Should I worry about fuse shrapnel and BANG! when it comes to fuse selection? D from BC -----------------------------------------------Reply----------------------------------------------- On Tue, 15 May 2007 04:17:37 GMT, D from BC <myrealaddr@comic.com> wrote: - Hide quoted text - >On Mon, 14 May 2007 09:38:01 -0700, Jim Thompson ><To-Email-Use-The-Envelope-I@My-Web-Site.com> wrote: >>On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >>wrote: >>>This is probably an oldie question on here... >>>I'd like to break the AC "hot" if there's too much AC current. >>>This would be due to a short or ground fault. >>>Or.... >>>Shunting the load to burn a fuse on the AC line would be ok too.. >>>I'm afraid that a fuse maybe too slow to protect the electronics from >>>burn out.. >>>Let's say the electronics I'm protecting cannot withstand 1.5x >>>overcurrent. >>>What's faster than a fuse on a AC line? >>>Details >>>Load: The load on the line is not a transformer and is not inductive. >>>Current draw: 2Amps >>>Line voltage: 240Vrms, 60Hz >>>Surge rate: guessing 45Amps in 1uS >>>Rule: 1/4watt current sense resistor. >>>The load circuit has a power bridge rectifier. >>>Maybe I could modify the bridge with transistors to interrupt the >>>surge current? >>>D from BC >>Years ago I used an SCR to blow fuses (on the load side). I think it >>was in the microsecond range. Warning, traces need to be fat, >>otherwise you blow traces instead of fuses... I had ~100A circulating >>momentarily to blow a 1 Amp fuse ;-) >> ...Jim Thompson >I'm wondering what's more explosive... >Slowly sneaking up the current through the fuse until it blows... >Or..... >suddenly connecting the fuse across a 300V charged 100uF low ESR >capacitor? >Should I worry about fuse shrapnel and BANG! when it comes to fuse >selection? >D from BC This was a conventional fast-blow fuse. It flashed like a flash-bulb (but not as much light) and made a tiny "click" ;-) The filament was completely plated out onto the glass. After we cracked a few, we went to the ceramic tube type. ...Jim Thompson -- \| James E.Thompson, P.E. \| mens \| \| Analog Innovations, Inc. \| et \| \| Analog/Mixed-Signal ASIC's and Discrete Systems \| manus \| \| Phoenix, Arizona Voice:(480)460-2350 \| \| \| E-mail Address at Website Fax:(480)460-2142 \| Brass Rat \| \| http://www.analog-innovations.com \| 1962 \| America: Land of the Free, Because of the Brave -----------------------------------------------Reply----------------------------------------------- D from BC wrote: > I'm wondering what's more explosive... > Slowly sneaking up the current through the fuse until it blows... > Or..... > suddenly connecting the fuse across a 300V charged 100uF low ESR > capacitor? Definitely the second. In the first case, the alloy just quietly melts. In the second, it vaporizes. > Should I worry about fuse shrapnel and BANG! when it comes to fuse > selection? If you exceed the fault current rating of the fuse, all bets for containment are off. -----------------------------------------------Reply----------------------------------------------- D from BC a crit : - Hide quoted text - > On Mon, 14 May 2007 11:40:08 -0700, John Larkin > <jjlar@highNOTlandTHIStechnologyPART.com> wrote: >> On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >> wrote: >>> This is probably an oldie question on here... >>> I'd like to break the AC "hot" if there's too much AC current. >>> This would be due to a short or ground fault. >>> Or.... >>> Shunting the load to burn a fuse on the AC line would be ok too.. >>> I'm afraid that a fuse maybe too slow to protect the electronics from >>> burn out.. >>> Let's say the electronics I'm protecting cannot withstand 1.5x >>> overcurrent. >>> What's faster than a fuse on a AC line? >>> Details >>> Load: The load on the line is not a transformer and is not inductive. >>> Current draw: 2Amps >>> Line voltage: 240Vrms, 60Hz >>> Surge rate: guessing 45Amps in 1uS >>> Rule: 1/4watt current sense resistor. >>> The load circuit has a power bridge rectifier. >>> Maybe I could modify the bridge with transistors to interrupt the >>> surge current? >>> D from BC >> One of our customers recently asked us to do that. He needs, >> basically, an SSR that also acts as a programmable circuit breaker >> and a current limiter. He needs to simulate cable faults and switch >> power circuits without exploding anything. We've been scribbling >> circuits for days, and it's non-trivial. We just a few minutes ago >> finished whiteboarding the design of a breadboard pcb so we can test >> the dynamics. >> John > To break a DC circuit, a pass transistor can be used.. Easy... > But breaking 240V AC...huhhh.. :( > I might look at using a little transformer to sense a current surge > and have that fire a shunt circuit until a fuse blows.. How about an AC current limiter? .--------------------------------. \| \| \| \| \| .---+---. \| \| \| \| \| \| .---+ \| .-. .-. \| \| \| \| \| \| \| \| \| \| +-\|\| .----+ \| \| \| \| \| - ->\|\| \| \| '-' '-' - ^ +-\|\|--' >\| \| \| ^ \| \| \|-+ +-\|<-+---. \| o-----+ +--. /\| \| \| \| \| +-------o \| .-. \| \| \| \| \| \| \| - \| \| \| ___ \| \|/ --- --- z - ^ \| \| '-\|___\|-+-\| --- --- A ^ \| '-' \|> \| \| \| \| AC in \| \| \| \| \| \| \| AC out '---+--------------+---+----\|---+----' .-. \| \| \| \| '-' \| o---------------------------------+----------------o -- Thanks, Fred. -----------------------------------------------Reply----------------------------------------------- On Tue, 15 May 2007 08:54:37 +0200, Fred Bartoli - Hide quoted text - <fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote: >D from BC a crit : >> On Mon, 14 May 2007 11:40:08 -0700, John Larkin >> <jjlar@highNOTlandTHIStechnologyPART.com> wrote: >>> On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >>> wrote: >>>> This is probably an oldie question on here... >>>> I'd like to break the AC "hot" if there's too much AC current. >>>> This would be due to a short or ground fault. >>>> Or.... >>>> Shunting the load to burn a fuse on the AC line would be ok too.. >>>> I'm afraid that a fuse maybe too slow to protect the electronics from >>>> burn out.. >>>> Let's say the electronics I'm protecting cannot withstand 1.5x >>>> overcurrent. >>>> What's faster than a fuse on a AC line? >>>> Details >>>> Load: The load on the line is not a transformer and is not inductive. >>>> Current draw: 2Amps >>>> Line voltage: 240Vrms, 60Hz >>>> Surge rate: guessing 45Amps in 1uS >>>> Rule: 1/4watt current sense resistor. >>>> The load circuit has a power bridge rectifier. >>>> Maybe I could modify the bridge with transistors to interrupt the >>>> surge current? >>>> D from BC >>> One of our customers recently asked us to do that. He needs, >>> basically, an SSR that also acts as a programmable circuit breaker >>> and a current limiter. He needs to simulate cable faults and switch >>> power circuits without exploding anything. We've been scribbling >>> circuits for days, and it's non-trivial. We just a few minutes ago >>> finished whiteboarding the design of a breadboard pcb so we can test >>> the dynamics. >>> John >> To break a DC circuit, a pass transistor can be used.. Easy... >> But breaking 240V AC...huhhh.. :( >> I might look at using a little transformer to sense a current surge >> and have that fire a shunt circuit until a fuse blows.. >How about an AC current limiter? > .--------------------------------. > \| \| > \| \| > \| .---+---. \| > \| \| \| \| \| > .---+ \| .-. .-. \| > \| \| \| \| \| \| \| \| > \| +-\|\| .----+ \| \| \| \| \| > - ->\|\| \| \| '-' '-' - > ^ +-\|\|--' >\| \| \| ^ > \| \| \|-+ +-\|<-+---. \| > o-----+ +--. /\| \| \| \| \| +-------o > \| .-. \| \| \| \| \| \| \| > - \| \| \| ___ \| \|/ --- --- z - > ^ \| \| '-\|___\|-+-\| --- --- A ^ > \| '-' \|> \| \| \| \| > AC in \| \| \| \| \| \| \| AC out > '---+--------------+---+----\|---+----' > .-. > \| \| > \| \| > '-' > \| > o---------------------------------+----------------o Arrrrghh... At first I couldn't figure this cct out.. The only way for current to pass is if the N Ch mos turns on. Otherwise the diodes block.. I see the bridge rectifier in this circuit.. Cool... I see the negative feedback loop from the Rsense through the NPN-PNP compound and back to the MOS that limits the AC current.. Is the AZ a zener? The circuit looks fast.. The only thing I don't like about this cct is that the current sensing resistor will be dissipating a nominal 1.2Watts in my app.. 0.6V2Amps= 1.2Watts.. 0.6V~=Vbe To use a smaller current sense resistor, I could use an op amp, but I'll be trading off speed... However...I might be able to come up with a transistor arrangement that uses a smaller (cooler) sense resistor.. Maybe I might try an SCR to shut down the mosfet... Or CMOS logic... It wouldn't be a limiter anymore but a breaker.. Thanks... Another circuit I'm looking at is http://www.google.com/patents?id=CKIVAAAAEBAJ&printsec=abstract&zoom=... Triac blowing line fuse. I think this also has a hot current sense resistor (If I=2amps and Itrip = 3Amps). D from BC -----------------------------------------------Reply----------------------------------------------- D from BC a crit : - Hide quoted text - > On Tue, 15 May 2007 08:54:37 +0200, Fred Bartoli > <fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote: >> D from BC a crit : >>> On Mon, 14 May 2007 11:40:08 -0700, John Larkin >>> <jjlar@highNOTlandTHIStechnologyPART.com> wrote: >>>> On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >>>> wrote: >>>>> This is probably an oldie question on here... >>>>> I'd like to break the AC "hot" if there's too much AC current. >>>>> This would be due to a short or ground fault. >>>>> Or.... >>>>> Shunting the load to burn a fuse on the AC line would be ok too.. >>>>> I'm afraid that a fuse maybe too slow to protect the electronics from >>>>> burn out.. >>>>> Let's say the electronics I'm protecting cannot withstand 1.5x >>>>> overcurrent. >>>>> What's faster than a fuse on a AC line? >>>>> Details >>>>> Load: The load on the line is not a transformer and is not inductive. >>>>> Current draw: 2Amps >>>>> Line voltage: 240Vrms, 60Hz >>>>> Surge rate: guessing 45Amps in 1uS >>>>> Rule: 1/4watt current sense resistor. >>>>> The load circuit has a power bridge rectifier. >>>>> Maybe I could modify the bridge with transistors to interrupt the >>>>> surge current? >>>>> D from BC >>>> One of our customers recently asked us to do that. He needs, >>>> basically, an SSR that also acts as a programmable circuit breaker >>>> and* a current limiter. He needs to simulate cable faults and switch >>>> power circuits without exploding anything. We've been scribbling >>>> circuits for days, and it's non-trivial. We just a few minutes ago >>>> finished whiteboarding the design of a breadboard pcb so we can test >>>> the dynamics. >>>> John >>> To break a DC circuit, a pass transistor can be used.. Easy... >>> But breaking 240V AC...huhhh.. :( >>> I might look at using a little transformer to sense a current surge >>> and have that fire a shunt circuit until a fuse blows.. >> How about an AC current limiter? >> .--------------------------------. >> \| \| >> \| \| >> \| .---+---. \| >> \| \| \| \| \| >> .---+ \| .-. .-. \| >> \| \| \| \| \| \| \| \| >> \| +-\|\| .----+ \| \| \| \| \| >> - ->\|\| \| \| '-' '-' - >> ^ +-\|\|--' >\| \| \| ^ >> \| \| \|-+ +-\|<-+---. \| >> o-----+ +--. /\| \| \| \| \| +-------o >> \| .-. \| \| \| \| \| \| \| >> - \| \| \| ___ \| \|/ --- --- z - >> ^ \| \| '-\|___\|-+-\| --- --- A ^ >> \| '-' \|> \| \| \| \| >> AC in \| \| \| \| \| \| \| AC out >> '---+--------------+---+----\|---+----' >> .-. >> \| \| >> \| \| >> '-' >> \| >> o---------------------------------+----------------o > Arrrrghh... > At first I couldn't figure this cct out.. > The only way for current to pass is if the N Ch mos turns on. > Otherwise the diodes block.. > I see the bridge rectifier in this circuit.. > Cool... > I see the negative feedback loop from the Rsense through the NPN-PNP > compound and back to the MOS that limits the AC current.. The positive FB loop between the NPN/PNP bjts make the 'limiter' trip. With the right time constants, the small bypass cap voltage gets down to the point where the 'SCR' self resets. This obviously has to happen within one line period (before injecting a new current pulse through the series RC). > Is the AZ a zener? Yep. Limits the gate voltage and provides a path for the RC branch 'negative half period' current. > The circuit looks fast.. Should be. > The only thing I don't like about this cct is that the current sensing > resistor will be dissipating a nominal 1.2Watts in my app.. > 0.6V2Amps= 1.2Watts.. > 0.6V~=Vbe > To use a smaller current sense resistor, I could use an op amp, but > I'll be trading off speed... > However...I might be able to come up with a transistor arrangement > that uses a smaller (cooler) sense resistor.. Can be fixed with just one more resistor. > Maybe I might try an SCR to shut down the mosfet... > Or CMOS logic... > It wouldn't be a limiter anymore but a breaker.. It is already. Well a periodic, self resetting one. -- Thanks, Fred. -----------------------------------------------Reply----------------------------------------------- "Fred Bartoli" <fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote in message news:46497209$0$18017$426a74cc@news.free.fr... - Hide quoted text - >D from BC a crit : >> On Tue, 15 May 2007 08:54:37 +0200, Fred Bartoli >> <fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote: >>> D from BC a crit : >>>> On Mon, 14 May 2007 11:40:08 -0700, John Larkin >>>> <jjlar@highNOTlandTHIStechnologyPART.com> wrote: >>>>> On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >>>>> wrote: >>>>>> This is probably an oldie question on here... >>>>>> I'd like to break the AC "hot" if there's too much AC current. >>>>>> This would be due to a short or ground fault. >>>>>> Or.... >>>>>> Shunting the load to burn a fuse on the AC line would be ok too.. >>>>>> I'm afraid that a fuse maybe too slow to protect the electronics from >>>>>> burn out.. >>>>>> Let's say the electronics I'm protecting cannot withstand 1.5x >>>>>> overcurrent. >>>>>> What's faster than a fuse on a AC line? >>>>>> Details >>>>>> Load: The load on the line is not a transformer and is not inductive. >>>>>> Current draw: 2Amps >>>>>> Line voltage: 240Vrms, 60Hz >>>>>> Surge rate: guessing 45Amps in 1uS >>>>>> Rule: 1/4watt current sense resistor. >>>>>> The load circuit has a power bridge rectifier. >>>>>> Maybe I could modify the bridge with transistors to interrupt the >>>>>> surge current? >>>>>> D from BC >>>>> One of our customers recently asked us to do that. He needs, >>>>> basically, an SSR that also acts as a programmable circuit breaker >>>>> and* a current limiter. He needs to simulate cable faults and switch >>>>> power circuits without exploding anything. We've been scribbling >>>>> circuits for days, and it's non-trivial. We just a few minutes ago >>>>> finished whiteboarding the design of a breadboard pcb so we can test >>>>> the dynamics. >>>>> John >>>> To break a DC circuit, a pass transistor can be used.. Easy... >>>> But breaking 240V AC...huhhh.. :( >>>> I might look at using a little transformer to sense a current surge >>>> and have that fire a shunt circuit until a fuse blows.. >>> How about an AC current limiter? >>> .--------------------------------. >>> \| \| >>> \| \| >>> \| .---+---. \| >>> \| \| \| \| \| >>> .---+ \| .-. .-. \| >>> \| \| \| \| \| \| \| \| >>> \| +-\|\| .----+ \| \| \| \| \| >>> - ->\|\| \| \| '-' '-' - >>> ^ +-\|\|--' >\| \| \| ^ >>> \| \| \|-+ +-\|<-+---. \| >>> o-----+ +--. /\| \| \| \| \| +-------o >>> \| .-. \| \| \| \| \| \| \| >>> - \| \| \| ___ \| \|/ --- --- z - >>> ^ \| \| '-\|___\|-+-\| --- --- A ^ >>> \| '-' \|> \| \| \| \| >>> AC in \| \| \| \| \| \| \| AC out >>> '---+--------------+---+----\|---+----' >>> .-. >>> \| \| >>> \| \| >>> '-' >>> \| >>> o---------------------------------+----------------o >> Arrrrghh... >> At first I couldn't figure this cct out.. >> The only way for current to pass is if the N Ch mos turns on. >> Otherwise the diodes block.. I see the bridge rectifier in this circuit.. >> Cool... >> I see the negative feedback loop from the Rsense through the NPN-PNP >> compound and back to the MOS that limits the AC current.. > The positive FB loop between the NPN/PNP bjts make the 'limiter' trip. > With the right time constants, the small bypass cap voltage gets down to > the point where the 'SCR' self resets. This obviously has to happen within > one line period (before injecting a new current pulse through the series > RC). >> Is the AZ a zener? > Yep. Limits the gate voltage and provides a path for the RC branch > 'negative half period' current. >> The circuit looks fast.. > Should be. >> The only thing I don't like about this cct is that the current sensing >> resistor will be dissipating a nominal 1.2Watts in my app.. >> 0.6V2Amps= 1.2Watts.. >> 0.6V~=Vbe >> To use a smaller current sense resistor, I could use an op amp, but >> I'll be trading off speed... >> However...I might be able to come up with a transistor arrangement >> that uses a smaller (cooler) sense resistor.. > Can be fixed with just one more resistor. >> Maybe I might try an SCR to shut down the mosfet... >> Or CMOS logic... >> It wouldn't be a limiter anymore but a breaker.. > It is already. Well a periodic, self resetting one. The power dissipated in the resistor is less than that, and as Fred says can be fixed easily (it isn't steady state, more like a sawtooth). I used something very similar as an inrush limiter on a SMPS a many years ago, and got bitten by * changing the fab that supplied the Mosfet just after we went into production. I forget the details, but it was to do with wimpy metallisation to the Mosfet gate - to turn the Mosfet off fast you have to pull the gate charge back out, which takes current. Regards Ian -----------------------------------------------Reply----------------------------------------------- "D from BC" <myrealaddr@comic.com> wrote in message news:o70i4314572ka2m7fd8g9u2ur9rc54s8t0@4ax.com... - Hide quoted text - > On Mon, 14 May 2007 13:43:15 -0500, John Fields > <jfie@austininstruments.com> wrote: >>On Mon, 14 May 2007 16:22:01 GMT, D from BC >><myrealaddr@comic.com> wrote: >>>This is probably an oldie question on here... >>>I'd like to break the AC "hot" if there's too much AC current. >>>This would be due to a short or ground fault. >>>Or.... >>>Shunting the load to burn a fuse on the AC line would be ok too.. >>>I'm afraid that a fuse maybe too slow to protect the electronics from >>>burn out.. >>>Let's say the electronics I'm protecting cannot withstand 1.5x >>>overcurrent. >>>What's faster than a fuse on a AC line? >>>Details >>>Load: The load on the line is not a transformer and is not inductive. >>>Current draw: 2Amps >>>Line voltage: 240Vrms, 60Hz >>>Surge rate: guessing 45Amps in 1uS >>>Rule: 1/4watt current sense resistor. >>>The load circuit has a power bridge rectifier. >>>Maybe I could modify the bridge with transistors to interrupt the >>>surge current? >>>D from BC >>--- >>How fast? > I might have to blow up some stuff to find out. :) > I'm just interested in rough ideas for various levels of cut-out > speed.. > Doesn't matter what cost, complexity or parts count. > At the moment, the faster ...the better.. > D from BC The fastest fuse in the world is an expensive microwave transistor. Works a treat to protect line fuses. Regards Ian -----------------------------------------------Reply----------------------------------------------- Ian a crit : - Hide quoted text - > "D from BC" <myrealaddr@comic.com> wrote in message > news:o70i4314572ka2m7fd8g9u2ur9rc54s8t0@4ax.com... >> On Mon, 14 May 2007 13:43:15 -0500, John Fields >> <jfie@austininstruments.com> wrote: >>> On Mon, 14 May 2007 16:22:01 GMT, D from BC >>> <myrealaddr@comic.com> wrote: >>>> This is probably an oldie question on here... >>>> I'd like to break the AC "hot" if there's too much AC current. >>>> This would be due to a short or ground fault. >>>> Or.... >>>> Shunting the load to burn a fuse on the AC line would be ok too.. >>>> I'm afraid that a fuse maybe too slow to protect the electronics from >>>> burn out.. >>>> Let's say the electronics I'm protecting cannot withstand 1.5x >>>> overcurrent. >>>> What's faster than a fuse on a AC line? >>>> Details >>>> Load: The load on the line is not a transformer and is not inductive. >>>> Current draw: 2Amps >>>> Line voltage: 240Vrms, 60Hz >>>> Surge rate: guessing 45Amps in 1uS >>>> Rule: 1/4watt current sense resistor. >>>> The load circuit has a power bridge rectifier. >>>> Maybe I could modify the bridge with transistors to interrupt the >>>> surge current? >>>> D from BC >>> --- >>> How fast? >> I might have to blow up some stuff to find out. :) >> I'm just interested in rough ideas for various levels of cut-out >> speed.. >> Doesn't matter what cost, complexity or parts count. >> At the moment, the faster ...the better.. >> D from BC > The fastest fuse in the world is an expensive microwave transistor. > Works a treat to protect line fuses. But you'll have to call your power company so that they speed up their generators quite a bit. -- Thanks, Fred. -----------------------------------------------Reply----------------------------------------------- On Tue, 15 May 2007 04:17:37 GMT, the renowned D from BC - Hide quoted text - <myrealaddr@comic.com> wrote: >On Mon, 14 May 2007 09:38:01 -0700, Jim Thompson ><To-Email-Use-The-Envelope-I@My-Web-Site.com> wrote: >>On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >>wrote: >>>This is probably an oldie question on here... >>>I'd like to break the AC "hot" if there's too much AC current. >>>This would be due to a short or ground fault. >>>Or.... >>>Shunting the load to burn a fuse on the AC line would be ok too.. >>>I'm afraid that a fuse maybe too slow to protect the electronics from >>>burn out.. >>>Let's say the electronics I'm protecting cannot withstand 1.5x >>>overcurrent. >>>What's faster than a fuse on a AC line? >>>Details >>>Load: The load on the line is not a transformer and is not inductive. >>>Current draw: 2Amps >>>Line voltage: 240Vrms, 60Hz >>>Surge rate: guessing 45Amps in 1uS >>>Rule: 1/4watt current sense resistor. >>>The load circuit has a power bridge rectifier. >>>Maybe I could modify the bridge with transistors to interrupt the >>>surge current? >>>D from BC >>Years ago I used an SCR to blow fuses (on the load side). I think it >>was in the microsecond range. Warning, traces need to be fat, >>otherwise you blow traces instead of fuses... I had ~100A circulating >>momentarily to blow a 1 Amp fuse ;-) >> ...Jim Thompson >I'm wondering what's more explosive... >Slowly sneaking up the current through the fuse until it blows... >Or..... >suddenly connecting the fuse across a 300V charged 100uF low ESR >capacitor? >Should I worry about fuse shrapnel and BANG! when it comes to fuse >selection? >D from BC I did tests, for example, on 5A 250V rated fuses. The 20mm glass variety would literally explode (a VERY loud bang) sending shrapnel everywhere, just on 240VAC/60Hz with an industrial source capable of enough source current. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" s@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -----------------------------------------------Reply----------------------------------------------- On May 14, 11:54 pm, Fred Bartoli - Hide quoted text - <fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote: > D from BC a crit : > > On Mon, 14 May 2007 11:40:08 -0700, John Larkin > > <jjlar@highNOTlandTHIStechnologyPART.com> wrote: > >> On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> > >> wrote: > >>> This is probably an oldie question on here... > >>> I'd like to break the AC "hot" if there's too much AC current. > >>> This would be due to a short or ground fault. > >>> Or.... > >>> Shunting the load to burn a fuse on the AC line would be ok too.. > >>> I'm afraid that a fuse maybe too slow to protect the electronics from > >>> burn out.. > >>> Let's say the electronics I'm protecting cannot withstand 1.5x > >>> overcurrent. > >>> What's faster than a fuse on a AC line? > >>> Details > >>> Load: The load on the line is not a transformer and is not inductive. > >>> Current draw: 2Amps > >>> Line voltage: 240Vrms, 60Hz > >>> Surge rate: guessing 45Amps in 1uS > >>> Rule: 1/4watt current sense resistor. > >>> The load circuit has a power bridge rectifier. > >>> Maybe I could modify the bridge with transistors to interrupt the > >>> surge current? > >>> D from BC > >> One of our customers recently asked us to do that. He needs, > >> basically, an SSR that also acts as a programmable circuit breaker > >> and a current limiter. He needs to simulate cable faults and switch > >> power circuits without exploding anything. We've been scribbling > >> circuits for days, and it's non-trivial. We just a few minutes ago > >> finished whiteboarding the design of a breadboard pcb so we can test > >> the dynamics. > >> John > > To break a DC circuit, a pass transistor can be used.. Easy... > > But breaking 240V AC...huhhh.. :( > > I might look at using a little transformer to sense a current surge > > and have that fire a shunt circuit until a fuse blows.. > How about an AC current limiter? > .--------------------------------. > \| \| > \| \| > \| .---+---. \| > \| \| \| \| \| > .---+ \| .-. .-. \| > \| \| \| \| \| \| \| \| > \| +-\|\| .----+ \| \| \| \| \| > - ->\|\| \| \| '-' '-' - > ^ +-\|\|--' >\| \| \| ^ > \| \| \|-+ +-\|<-+---. \| > o-----+ +--. /\| \| \| \| \| +-------o > \| .-. \| \| \| \| \| \| \| > - \| \| \| ___ \| \|/ --- --- z - > ^ \| \| '-\|___\|-+-\| --- --- A ^ > \| '-' \|> \| \| \| \| > AC in \| \| \| \| \| \| \| AC out > '---+--------------+---+----\|---+----' > .-. > \| \| > \| \| > '-' > \| > o---------------------------------+----------------o I worry a bit about the forward current on the Zener. I guess that with the values put in, the current will be small enough. Also if you don't mind a little leakage: Modified version: - Hide quoted text - > .--------------------------------. > \| \| > \| \| > \| .---. \| > +----------. \| \| \| > .---+ \| \| .-. \| > \| \| \| \| \| \| \| > \| +-\|\| .--------+ \| \| \| > - ->\|\| \| \| \| '-' - > ^ +-\|\|--' - \| \| ^ > \| \| \| \| \| +-\|<-+---. \| > o-----+ +--. \| \| \| \| \| \| +-------o > \| .-. \| - \| \| \| \| \| > - \| \| \| ___ \| \|/ \| \| \| - > ^ \| \| '-\|___\|-+-\| --- --- z ^ > \| '-' \|> --- --- A \| > AC in \| \| \| \| \| \| \| AC out > '---+--------------+---+----\|---+----' > .-. > \| \| > \| \| > '-' > \| > o---------------------------------+----------------o It relies on the device capacitances to hold the NPN on through the zero crossing. -----------------------------------------------Reply----------------------------------------------- MooseFET a crit : - Hide quoted text - > On May 14, 11:54 pm, Fred Bartoli > <fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote: >> D from BC a crit : >>> On Mon, 14 May 2007 11:40:08 -0700, John Larkin >>> <jjlar@highNOTlandTHIStechnologyPART.com> wrote: >>>> On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr@comic.com> >>>> wrote: >>>>> This is probably an oldie question on here... >>>>> I'd like to break the AC "hot" if there's too much AC current. >>>>> This would be due to a short or ground fault. >>>>> Or.... >>>>> Shunting the load to burn a fuse on the AC line would be ok too.. >>>>> I'm afraid that a fuse maybe too slow to protect the electronics from >>>>> burn out.. >>>>> Let's say the electronics I'm protecting cannot withstand 1.5x >>>>> overcurrent. >>>>> What's faster than a fuse on a AC line? >>>>> Details >>>>> Load: The load on the line is not a transformer and is not inductive. >>>>> Current draw: 2Amps >>>>> Line voltage: 240Vrms, 60Hz >>>>> Surge rate: guessing 45Amps in 1uS >>>>> Rule: 1/4watt current sense resistor. >>>>> The load circuit has a power bridge rectifier. >>>>> Maybe I could modify the bridge with transistors to interrupt the >>>>> surge current? >>>>> D from BC >>>> One of our customers recently asked us to do that. He needs, >>>> basically, an SSR that also acts as a programmable circuit breaker >>>> and a current limiter. He needs to simulate cable faults and switch >>>> power circuits without exploding anything. We've been scribbling >>>> circuits for days, and it's non-trivial. We just a few minutes ago >>>> finished whiteboarding the design of a breadboard pcb so we can test >>>> the dynamics. >>>> John >>> To break a DC circuit, a pass transistor can be used.. Easy... >>> But breaking 240V AC...huhhh.. :( >>> I might look at using a little transformer to sense a current surge >>> and have that fire a shunt circuit until a fuse blows.. >> How about an AC current limiter? >> .--------------------------------. >> \| \| >> \| \| >> \| .---+---. \| >> \| \| \| \| \| >> .---+ \| .-. .-. \| >> \| \| \| \| \| \| \| \| >> \| +-\|\| .----+ \| \| \| \| \| >> - ->\|\| \| \| '-' '-' - >> ^ +-\|\|--' >\| \| \| ^ >> \| \| \|-+ +-\|<-+---. \| >> o-----+ +--. /\| \| \| \| \| +-------o >> \| .-. \| \| \| \| \| \| \| >> - \| \| \| ___ \| \|/ --- --- z - >> ^ \| \| '-\|___\|-+-\| --- --- A ^ >> \| '-' \|> \| \| \| \| >> AC in \| \| \| \| \| \| \| AC out >> '---+--------------+---+----\|---+----' >> .-. >> \| \| >> \| \| >> '-' >> \| >> o---------------------------------+----------------o > I worry a bit about the forward current on the Zener. I guess that > with the values put in, the current will be small enough. Under normal working conditions (no tripping/limiting) the supply has no current to provide (just biasing the gate), so the average (or even peak) current can be made 1mA without any pb. - Hide quoted text - > Also if you don't mind a little leakage: > Modified version: >> .--------------------------------. >> \| \| >> \| \| >> \| .---. \| >> +----------. \| \| \| >> .---+ \| \| .-. \| >> \| \| \| \| \| \| \| >> \| +-\|\| .--------+ \| \| \| >> - ->\|\| \| \| \| '-' - >> ^ +-\|\|--' - \| \| ^ >> \| \| \| \| \| +-\|<-+---. \| >> o-----+ +--. \| \| \| \| \| \| +-------o >> \| .-. \| - \| \| \| \| \| >> - \| \| \| ___ \| \|/ \| \| \| - >> ^ \| \| '-\|___\|-+-\| --- --- z ^ >> \| '-' \|> --- --- A \| >> AC in \| \| \| \| \| \| \| AC out >> '---+--------------+---+----\|---+----' >> .-. >> \| \| >> \| \| >> '-' >> \| >> o---------------------------------+----------------o > It relies on the device capacitances to hold the NPN on through the > zero crossing. Ok, but it doesn't trip, so you'll need some very serious heat sinking under fault conditions. -- Thanks, Fred.

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Electronic circuit design discusions

Fastest AC Electronic Fuse