Power Control Circuit

The easiest way is to use a microprocessor that can run at very low current, and don't actually turn the micro off -- just turn off everything else and power the micro down to an absolute minimum.

Thanks Tim, The issue is that I actually shut down the regulators. I am looking at something like this:

Rich

The USB can only give you 500mA normally and maybe 1 amp max at full power. Maybe I miss understood your needs?

Jamie

That p-fet is drawn wrong. That's a problem with using that symbol.

I don't know what parts you're having trouble with.

For the actual brains you can use an RS flip-flop, reset it on power-up, and set it when I want power to go off. If you use the right CMOS family of parts it won't consume any power to write home about, and if USB +5V can be depended on (I don't know -- that's for you to check) you don't need any regulation into it.

For the power stage -- well, it sounds like you have a published plan.

It's pretty much the same as the symbol in the manufacturer's datasheet. But then what do IR know ?-)

piglet

up from USB VBUS (5V) when a cable is plugged in. I need the ability to t urn turn off that connection from a microcontroller. If the user unplugs a nd reinsert the cable the circuit powers back up.

There are various ways to do it. One example is to supply power to the micr o via a cap that gives a short pulse only, and have the micro turn on a fet /tr/ that bypasses the cap. Now it can switch itself off any time.

Why though... micros can normally power down anyway.

NT

Apart from the weird zener, which isn't in the standard PFET symbol, it looks fine to me. (I expect it indicates an avalanche-rated FET.) What am I missing?

For reverse polarity protection you'd interchange source and drain, ground the gate via a resistor, and (for extra credit) put a zener from gate to source to prevent punchthrough. The DS diode is useful there, because it's what makes the FET turn on reliably at power-up, and the symbol shows how it works. We'll just have to continue to disagree about that, as we do about whether crawfish etoufee counts as a foodstuff.

Cheers

Phil Hobbs

Oh, my! Crawfish Etouffee certainly does count as a foodstuff. I was contemplating a nice prime rib for our afternoon brunch, but you changed my mind... off to the "Angry Crab" ;-) ...Jim Thompson

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Local crawfish from the neighbourhood arroyo? Probably taste better with a bit of diesel fuel added. ;)

But it's all good--more roast beef for the rest of us.

Cheers

Phil Hobbs

No it's not, unless with 'pretty much' you mean 'not exactly':

Although, like you, I don't see any problem, as the arrow indicating the np junction to source already makes it clear where the source is. So it's not ambiguous how he drew it.

joe

Never mind, it's OK.

I guess the zener suggests avalanche rating.

(Weenie load because all I had for a discrete PMOS Spice model was a weenie PMOS :-) ...Jim Thompson

RevB...

...Jim Thompson