Electronic fuse
in [Design]
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From: dagmargoodboat on 5 Jul 2010 02:10 On Jul 4, 7:14 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > > The polyfuse is looking better and better. They're not as bad as I thought. I mistook the max resistance number to mean when tripped, but that's not the case. With that clarified the polyfuse is slow, but not horrible for short- circuit protection. > Foldbacks can have strange behavior with some non-resistive loads. > That's why a shutdown with periodic retry is good. > > Hey, have a uP port pin turn on a series PNP or pfet, and use a spare > ADC channel to digitize the load voltage. Then do the math. I'm doing > some fairly complex shutdowns in software on the 4-20 mA gadget we're > doing... software lowpass filtering, trip thresholds, automatic retry, > stuff like that. Another thing I like to do is measure power fet > voltage and current and heatsink temp, run a realtime simulation of > thermal dynamics, and shut down based on junction temperature. You could've just said "Use a PIC." -- Cheers, James Arthur
From: Tim Williams on 5 Jul 2010 02:11 <dagmargoodboat(a)yahoo.com> wrote in message news:f89a6ee7-3455-4051-890e-5dff42cc8ee0(a)b35g2000yqi.googlegroups.com... > http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Motor_Thin... > > Spike-zilla! (How do you avoid big shoot-through currents? High Vth > FETs?) Yes, there will be lots of shoot through. Hopefully under a microsecond, which will abuse the supply, a good reason to have it connected on long wires. Poor enough wire is self snubbing. :-p It's only one edge (assuming no bounce, which if the supply drops below 5V, the 4001 could reset; but, it won't go less than 2*Vgs(th), so it can't be too terrible), so the average dissipation is small. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 5 Jul 2010 02:14 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:2m72361nrmtpe7vkuet21mh8bnuqvdld1r(a)4ax.com... > Or maybe one of these... > > ftp://jjlarkin.lmi.net/Goofy_Ilims.JPG > > > The polyfuse is looking better and better. The bottom one would be particularly good with a TLV431. Well, maybe with a schottky to keep supply current into it. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Larkin on 5 Jul 2010 12:10 On Mon, 5 Jul 2010 01:14:21 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:2m72361nrmtpe7vkuet21mh8bnuqvdld1r(a)4ax.com... >> Or maybe one of these... >> >> ftp://jjlarkin.lmi.net/Goofy_Ilims.JPG >> >> >> The polyfuse is looking better and better. > >The bottom one would be particularly good with a TLV431. Well, maybe with a schottky to keep supply current into it. > >Tim Sure, it you're one of those people who fling 13 cents around as if it didn't matter. That's the upper circuit here ftp://jjlarkin.lmi.net/Goofy_lims_2.JPG which suggests the lower one. Add a cap somewhere for surges/spikes maybe. 5 parts, 9 cents total, including a cap. Interesting little circuit, actually, a flipflop of sorts. John
From: Jim Thompson on 5 Jul 2010 12:13
On Mon, 05 Jul 2010 09:10:33 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 5 Jul 2010 01:14:21 -0500, "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:2m72361nrmtpe7vkuet21mh8bnuqvdld1r(a)4ax.com... >>> Or maybe one of these... >>> >>> ftp://jjlarkin.lmi.net/Goofy_Ilims.JPG >>> >>> >>> The polyfuse is looking better and better. >> >>The bottom one would be particularly good with a TLV431. Well, maybe with a schottky to keep supply current into it. >> >>Tim > >Sure, it you're one of those people who fling 13 cents around as if it >didn't matter. > >That's the upper circuit here > >ftp://jjlarkin.lmi.net/Goofy_lims_2.JPG > >which suggests the lower one. Add a cap somewhere for surges/spikes >maybe. 5 parts, 9 cents total, including a cap. Interesting little >circuit, actually, a flipflop of sorts. > >John > Newbies are invited to LTspice it, testing it with various element values. ...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 | Obama: A reincarnation of Nixon, narcissistically posing in politically-correct black-face, but with fewer scruples. |