Who makes those combined polyfuse/TVS overload protectors?
I accidentally blew up a box that was protected by a polyfuse followed by a transzorb. I applied 24 volts to a 15-volt box, and the power supply current limited just below the polyfuse trip current, so I toasted the 15 volt transzorb. That's improbable, but not nice.
If the transzorb heated the polyfuse, it would be safer. I think someone makes that, but I don't recall who.
Tyco PolyZens. They're the bomb.
Cheers
Phil Hobbs
Also, with some care you can put another transzorb in series with the PZ's ground lead to get higher voltages. Probably needs an antiparallel diode to keep the polarity protection then.
Cheers
Phil Hobbs
Yeah, the TE parts only go up to 16 volts; I need 24. A 6 or 8 volt TVS below might work. Wouldn't there still be reverse protection?
A crowbar could replace the TVS in my circuit, I guess.
I could glue my leaded polyfuse to the top of a couple of series'd TVSs, but that would be messy.
There would, but 2 diode drops instead of 1, which could be enough to cause problems at high fault currents, I expect. I'm a big fan of Schottky rectifiers for that job--my protos all have 1N5822s on the supplies. (The big beefy leads are also convenient places to hang scope probes and clip leads.)
Also slower. PolyZens act almost like voltage regulators. Plus hotmelt would be counterproductive. ;)
Cheers
Phil Hobbs
Don't worry about it, John. I blow things up every day here. You get used to it after a while.
I usually prefer to blow things up on purpose. I did borrow the
15-volt box from C, for a thermal test, and it was mildly embarassing to give it back to her destroyed.We will supply the new box with a 24-volt wall-wart. There aren't many warts over 24, so maybe I shouldn't worry about somebody grabbing the wrong supply and blowing things up. So polyfuse and unipolar TVS is probably OK.
The TE things only go to 16 volts.
Power supplies can be a real pain. I'll be lucky if I only have 10 rails. And if the switcher wart is stable driving the switchers in the box.
some equipment that has power-over-ethernet as an option wants a 48V supply, some Cisco IP telephones are like that.
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