Need a simple DC output current limiter

This would be a better button:

Recently on a TV drama show someone got zapped on each side of the head with a defibrillator - what would that actually do?

Ouch! I have never seen that. Only heard about some electric-shock therapy for mental patients but that sounds gruesome.

Obviously it was fiction (Terminator -The Sarah Conner Chronicles) but it would be interesting to look at the energy levels involved and try predicting what damage it would do.

It's probably cure leftist weenies... maybe. More likely you'd need to give them a frontal lobotomy ;-)

...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Sounds like you've already had some.

If it had enough energy availible it would work like the old 'hot dogger'!

therapy

Certainly not ISO 9001.

e a

The output is one of many, so essential is to not let one shorted output draw down the common PSU for these outputs. Thats why the PTC solution won't work since the current limit point at -40 degrees is very high and that would spec the PSU for very high current (in case

It doesn't have to trip fast, but it cannot trip at a to high current. Nominal is 350mA, maximum would be something like 500mA. The real consern is a shorted output needs to be controlled so the pass device is not destroyed (fast current sense and enough thermal mass to handle a brief short)

Regards

Klaus

Good idea.

I did scan a lot of LDOs and standard regs, but found none with a precise and setable current limits. Many limited to the thermal limit, but then thats dependable on the ambient temperature....

Regards

Klaus

Klaus, Do you have room for the LM317 current limit scheme?

Message-ID:

Only "brief" shorts, or do you need fold-back?

...Jim Thompson

I did look at the '317 solution and it is appealing since it also provides plenty second source components. Also we have a design need for a feedback that signal if the output is valid (no short etc), so we could add a micro for that and let that monitor all the outputs to catch a current limited '317 and shutoff before the thermal limit is reached (due to UL regulatory demands)

Regards

Klaus

trips

method

dependancy.

trip

several=20

with=20

I suspect that if it really happened it would kill outright.

ip

e to

have a

Yes, there's plenty of room. I would however like to keep it in SMD packages, so the D2PAK is an obvious choice. But at max 1.5V dropout voltage the loss is 500mW which will raise the junction by 35degrees. And thats with a large PCB area as heatsink (0.5sq inch)

Is there a industry standard LDO (read: second sourced), so I can get rid of that power loss? (allthough I don't like LDO's due to stability issues)

Regards

Klaus

The problem is connecting as a current source. I don't (personally) know of an LDO that will do that.

...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I dread to think what the coffee cup immersion heater got used for before hazing was banned!!!

Since the LM317 would go into shutdown mode as the ADJ to OUT voltage reaches 1.25V that could be done using a couple of resistors and a PNP transistor. It would pull up when exceeding a certain current (but has to be limited to the logic rail so at least one more resistor). Unfortunately 1.25V ain't enough for a low cost optocoupler.

Also, the LM317 solution will cause some dropout voltage and the "sense resistor" needs the right wattage which is a bit of a downside if space is tight.

I'd go one further: I wouldn't trust any LDO to do that job ;-)

When I was at MIT there was no hazing. That came in the late '90's, and was promptly snuffed.

We did have a few frat houses banned for wild parties ;-)

(I was never in a frat. Lived two years in the dorms, Burton House, then Goodale, then married and moved to the third floor of a house in Cambridge, near Stop and Shop ;-)

...Jim Thompson