wart overvoltage protection

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.

2576 switches at 50 KHz with nice soft edges. It needs an external schottky so there's no shoot-through current spike.

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

17v parts around.

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

almost 10k in stock for ~1$ each

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 ..

But you don't know where it's been. It might not even be a real TI part.

søndag den 2. oktober 2022 kl. 20.05.14 UTC+2 skrev John Larkin:

it's LCSC not some dodgy ebay shop

Coincidentally, I recently ordered a couple of hundred of those on spec, for like $66.

They are a bit suspicious in that the 100-piece price is considerably lower than TI's, but we'll see.

Cheers

Phil Hobbs

Reverse protection is also important to protect against an input short, which can blow up stuff by forcing currents from output to input.

That's one of the three ways to blow up a 317, and one of the two to blow up an 78xx regulator. (Input overvoltage is the other main one, and for a 317, discharging a big ADJ pin bypass backwards.

Cheers

Phil Hobbs

Texas Instruments parts are made in Chengdu High-tech Zone (CDHT) in Chengdu, a city in the southwestern region of China and considered by many to be China's next major technology hub.

LCSC is in Shenzhen, so they have access to lower prices.

The LM5164 has no reverse polarity protection, but that is solved with a simple series diode.

Correction: With a presence in Hong Kong since 1967 and in the China mainland since 1986, TI's strategy in China has always been about putting resources closer to its customer base. TI has employees in sales and marketing, research and development and now manufacturing in a total of 16 cities in China: Beijing, Shanghai, Guangzhou, Shenzhen, Chengdu, Nanjing, Xi'an, Wuhan, Xiamen, Dongguan, Zhuhai, Nanjing, Qingdao, Suzhou, Hangzhou and Hong Kong.

I got tripped up on this recently. What'd weird is that without the body diode, the source and drain must be connected in the expected direction (and it sorta works) but with the body diode, it *must* be in the reverse direction. Very confusing at first sight.

Clifford Heath.

fets without a body diode are very rare

The EPC gan parts don't exactly have a body diode, but turn on soft at around -2 volts. Somehow.

I first saw the PFET polarity protector in an article by Bob Pease, circa 2005. It's pretty cute, actually.

Cheers

Phil Hobbs