wart overvoltage protection (2023 Update)

We make a gadget that's powered by a 12 volt wart, and sometimes a user applies 24 and blows one up.

We have a polyfuse and a 12 volt TVS and they sometimes fry the TVS. It's posssible that most any useful polyfuse+TVS combo can be teased to destruction.

I think Phil H mentioned some gadget, a polyzorb or something, that would be better. I can't find it.

We might fine-tune the polyfuse+TVS, or maybe go polyfuse and SCR crowbar, or something.

This is all entangled with parts availabity. Ideally the box would just work from 12 or 24, but that has separate complications.

We once used a TI electronic fuse IC, but it liked to blow up.

Reply to
John Larkin
Loading thread data ...

Have some series resistance to work at 24v, and switch the resistance out if the voltage drops er stays under 13v?

Cheers

Reply to
Martin Rid

Tyco PolyZens were amazing, but unfortunately they were available for only a few years. I think they had to have too many part numbers to fill all the (current, voltage) space.

It was a pretty slick idea, laminating the TVS and polyswitch together so that you couldn't fry the one without switching the other.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Or maybe an LM393 and a PFET.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

That's an idea, a pfet current limiter that entirely shuts off if the input goes above maybe 14 volts. At maybe a 500 mA, fet dissipation would be OK.

Someone here suggested making our own polyzen sort of thing, but I suspect we couldn't successfully transfer the heat from the TVS to the polyfuse fast enough.

An SMB12A TVS is rated for peak power, 600 watts, but not rated for DC power. 5 watts maybe with big pads?

Reply to
John Larkin

So, is the power inlet clearly laser-burn-marked as 12V center positive? And is the supplied power brick similarly clearly labeled?

Reply to
whit3rd

On a sunny day (Fri, 30 Sep 2022 13:14:03 -0700) it happened John Larkin <jlarkin@highland_atwork_technology.com> wrote in snipped-for-privacy@4ax.com:

Better switcher regulator that accepts up to 24 V

Reply to
Jan Panteltje

I've occasionally looked at the specialized OVP/power limiter chips, but they tend to cost $$$, and for my purposes they don't look as good as doing the limiting locally. (If I were controlling big motors or something, that might be a different matter.)

At various times I've used LP2951s to make small amounts of +3.3V directly from the wall wart to run startup circuitry and so forth. An LM393 is a 358 with different metal--the input devices are lateral PNPs, and so will take a lot of positive voltage regardless of the supplies.

A few microseconds of delay is no problem for that job.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Crowbar circuit?

Sylvia.

Reply to
Sylvia Else

-----------------------

** See JL's first post, forth para.

..... Phil

Reply to
Phil Allison

Yes.

I like crowbars. No finesse required.

Sylvia.

Reply to
Sylvia Else

A few years back the late Jim Thompson of this very bazaar posted a circuit using two TL431 and two pmos fets to provide series undervolt, overvolt and reverse polarity protection. All jelly bean very low cost parts in unlimited supply?

piglet

Reply to
piglet

We tried the TPS26600 "hot swap efuse" and it liked to blow up. It's a horrible complex expensive power-pad thing.

I might just start with an LM2576 and switch down to maybe +7, and work from there. That will work from 10 to 40 volts. 2576 is an old, slow, klunky, non-synch switcher that's available. Wonderful part.

We could assume the dpak but we might lead-form the TO220 version in a pinch. TO220s seem to be available. Maybe nobody wants them.

The guys wanted to use the LT8603 quad switcher but we tested it and it makes nasty 400 MHz ringy things at the switching edges. In a "silent switcher" !

We used the LTM8078 dual BGA module and had a similar problem; it sprayed huge RF bursts all over the board. Probably the same technology. The nasties are on both edges, so it's just switching too fast, not an SRD effect.

formatting link
Had to redesign the big control board.

Reply to
John Larkin

A polyfuse isn't a bad thing, to prevent blowing traces off a board worst-case. I'm emotionally opposed to using semiconductors to protect semiconductors from power blunders.

Poly + diode handles the reversed supply situation OK. I've just got to handle the overvoltage case somehow.

We only use leaded polyfuses, the ones that look like disc caps. The surface-mount ones are generally bad news.

Polyfuse + TVS can fail, but the TVS shorts, sort of like the skinny guy jumping on top a hand grenade. Why didn't everybody just run?

Reply to
John Larkin

Yes, but in a tangle of wart cords, people sometimes make mistakes. It is prudent for instruments to be rugged. All our new stuff uses +24.

It's unfortunate that barrel connectors weren't keyed for voltages. Or even marked.

Reply to
John Larkin

That would work, with a polyfuse and a big diode for reverse voltage. I can get a dpak SCR that will handle 50 amps for a while.

Just a zener to the gate of an SCR is probably OK for modest short-circuit currents. Big crowbars need a fast gate driver, diac or something.

Reply to
John Larkin

Sigh! Many connectors, coax or otherwise, seem designed to maximize trouble.

Jeroen Belleman

Reply to
Jeroen Belleman

Does your 24V supply have short circuit protection? If so, i would use TL431 and IGBT to shunt it. RJP30E2: 200A peak in TO-220 package.

Reply to
Ed Lee

I use a fair number of the 150-kHz ones--they're still nice and slow and stupid, but use smaller and cheaper inductors.

Yeah, and the predominant frequency changes depending on the trace lengths you're got attached. We had one horrible failure on a small board with three switchers on it--two worked fine, but the LMR23630 we were using to make -12 from +13 produced a VHF-fest like yours.

One one trace it was mostly near 180 MHz, but on another it was 125ish. We gave up.

Yecch.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

I mirror his website at

formatting link
. Cheers

Phil Hobbs

Reply to
Phil Hobbs

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.