wart overvoltage protection (2023 Update)

This is one of my favorite waveforms:

We ship this particular box with a small 12 volt wart, but a customer might use some other supply in a system application. They do sometimes apply 24 and blow up the TVS.

The ideal product handles up to +-48 at zero source impedance and behaves gracefully for any combination of brownouts and fumble-fingers.

Any decent power supply should be able to handle half-short circuit. Put in a big heat sink and it might just work with 24V supply, shunt to 12V.

lørdag den 1. oktober 2022 kl. 21.23.38 UTC+2 skrev John Larkin:

TPS2400 add PFET for reverse voltage protection

TPS2400 has Vin max of 6.8V. TL431 can go up to 30V.

I thought the usual go was to short circuit the current long enough to blow a conventional fuse. Of course, you have to handle the case where the PS cannot supply enough current to blow the fuse, but sits there and fizzles instead.

Or is even fuse replacement beyond the customer's competence? Would you need to confiscate everything conductive and fuse sized first?

Sylvia.

On a sunny day (Sat, 01 Oct 2022 12:23:27 -0700) it happened John Larkin snipped-for-privacy@highlandSNIPMEtechnology.com wrote in snipped-for-privacy@4ax.com:

From datasheet quote: LM2576/LM2576HV Series SIMPLE SWITCHER ® 3A Step-Down Voltage Regulator General Description Features The LM2576 series of regulators are monolithic integrated n 3.3V, 5V, 12V, 15V, and adjustable output versions circuits that provide all the active functions for a step-down n Adjustable version output voltage range, (buck) switching regulator, capable of driving 3A load with 1.23V to 37V (57V for HV version) ± 4% max over excellent line and load regulation. These devices are avail- line and load conditions able in fixed output voltages of 3.3V, 5V, 12V, 15V, and an n Guaranteed 3A output current adjustable output version. n Wide input voltage range, 40V up to 60V for Requiring a minimum number of external components, these HV version

So HV version, preceded by bridge rectifier and insulated wart input. Used this chip, did not see ultra short spikes but I have no femtosecond capable scope...

Sylvia Else wrote: =============

Will trip at 13V with normal polarity and about 1.5V reverse. Anyone stupid enough to use the wrong voltage/ polarity wall wart deserves to see it die.

..... Phil

It can be done wrong.

Soft gate drive can be a hazard.

Zener+triac could allow a couple of volts of negative swing.

Except that said stupid person will ship it back for us to fix.

A polyfuse doesn't need a fuse holder and doesn't need to be replaced. There's no room in our small boxes for an external-access type fuse holder anyhow.

If the wart current limits before the poly opens up, that's OK. Warts do current limit. Some DC, some burp mode.

But some customers run our stuff off a big DC bus with maybe a 20 amp breaker somewhere.

That would work if the LDO can stand +24v input. It still needs reverse protection.

May as well just let it work from +10 to +40. The customer can use the wrong wart and never notice the difference.

I suspect that negative-center warts are rare these days.

My next problem is a bulletproof UVLO and switcher sequencing.

søndag den 2. oktober 2022 kl. 17.11.23 UTC+2 skrev John Larkin:

if it is always from an isolated wallwart, a bridge rectifier?

LM5164 ?

Maybe not available.

We have LM2576HV in stock, and the regular, non-HV (40 volts max) version seems to be available. Slow and quiet. So I'll probably go polyfuse, negative clamp diode, LM2576 to +7 and work down from there.

TI makes a zillion versions of their adorable little 6-pin synchronous switchers and some are available in reel quantity. I won't name my pick until we have a reel or two on the way.

TPS54302 is good for 28v in but is hard to get. There are tons of the

søndag den 2. oktober 2022 kl. 18.55.09 UTC+2 skrev John Larkin:

We don't buy "asian brands."

We have LM2576 in stock and in our PCB library, and it's available from authorized distributors.

søndag den 2. oktober 2022 kl. 19.11.26 UTC+2 skrev John Larkin:

"asian brands."? it is a TI part ..