No current sense resistor required for MOSFET switch protection

I sort of doubt it.

John

Post a schematic or show a link. ...Jim Thompson

That's okay. Forgot to add >

Oh sure!

Still doubt it. Show us.

John

We'd be happy to analyze your circuit, and point out where it fails to do what you think its doing.

"oparr" doesn't know he's about to bite the dust and look like an idiot ;-) ...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

Well, there's >

There are well kept secrets in everyday electronics.

He's a Larkin spin-off... allusions/illusions of grandeur :-) ...Jim Thompson

Since you won't reveal your circuit, maybe you can explain your business model to us.

John

He can do most of that (if he's prepared to be crappy enough) by using one of those beta-dependent BJT circuits of yours--stick a BJT in series with the source of the MOSFET, and give it just enough base current to almost saturate at the highest current you want to allow.

NOT how you'd want to do it in real life, but it'd limit the current and so on.

Cheers

Phil Hobbs

That would work at the microamp sort of level. Not very useful.

The thing I like about beta limiting, in addition to its electrical virtues, is that everybody has been taught many, many times to never, never do it. I can't pass up a challenge like that. People who will cheerfully use a jfet with 10:1 Idss ratings won't consider beta design using a BCX71K with a less than 2:1 HFE spread.

I really like the Supertex depletion fets as signal-level protectors.

John

Yep. Larkin's magic bag of tricks can certainly give one heartburn ;-) ...Jim Thompson

Hell! I regularly design around PNP's with a worst-case beta of 1 (yep, one!)

I love chip processes that have depletion-mode FET's... just great for Bandgap starters. ...Jim Thompson

Don't all fabs have JFETs? Maybe not defined and 'scoped out, but aren't they at least able to accommodate them if you roll your own?

Some fabs have an N-well resistor that is sort of a JFET. The problem is you want one that cuts off sharply enough that start-up goes away completely. I've only seen a few useable for low voltage circuits, such as in RFID tags. ...Jim Thompson