more whining

What I want is an LM317 in SOT-23. Haven't found it yet, and thousands of ldo's don't help.

John

Oh, quit whining. ;-)

Less of a whine, more of a rumble, but here's a sign of more money than sense..

Best regards, Spehro Pefhany

Hello John,

Sometimes the old discrete solution remains the best. I find that many times in my designs. Lots of 3904, BAV99 and stuff like that. Can't really beat the prices, with 0402 resistors costing under 1/2c.

Hello Frank,

The 80% doesn't matter because much of the stuff will go dormant after shutting down. What matters is the cumulative current draw of all systems. However, it still needs some juice to keep things like a realtime clock going. A microamp or so. When the circuit wakes up then all kinds of other electrical gear will be going. Fans, A/C, lights, radio etc.

The chip is more geared towards automotive but with a zener you can get it into the right range. There isn't much choice for 24V systems, you've got to make do with what's there, or design a discrete circuit which is what I often decide to do.

That's expensive.

Best regards, Spehro Pefhany

Hello Jim,

Yaaaaawn...

Now I remember why I quit subscribing to paper issues of such magazines a long time ago.

Hello Jim,

With a BSS123? About 4-5 cents.

spendthrift! I'd use an 8050 and three resistors. Well under a penny, and output close enough to zero/Vcc for practical purposes.

Best regards, Spehro Pefhany

What, and go Off Topic?

Now that is bizarre. Why not just put a stick of dynamite in it?

John

In order to get the cheap magazine mailing rate, USPS regs require a certain amount of "editorial content", but the regs don't address the quality of same. And all the people who work for the mags are journalism majors.

John

Get rid of the comparator. Poke the signal directly into the base of a cheap NPN transistor, and pull up the collector.

John

John, You're becoming a hacker ;-)

...Jim Thompson

No, it's just easy for beginners to confuse hacking with elegance.

John

Really ?:-) A NPN detects ZERO crossings?? And you left out a base resistor in your hack ;-)

...Jim Thompson

Well, you never defined zero, and I'd use a resistor if it needed one.

Now, this vanilla cream blueberry brioche is elegant. I knew there had to be a reason to locate an electronics company in a place like this.

How about this...

John

Hello John,

Sad. That would mean that some magazines might slowly degenerate to mere ad pamphlets.

Hello Spehro,

Well, Jim capitalized "zero" so I figured he'd want it to within 10mV or so :-)

Then there'd be the inverted transistor rectifier, might get it close enough as well. Another option could be to run a comparator between 0V and 5V and fudge its input common mode range. Might need a dual BAT54 though and that would add around 2c :-(

Nothing to limit base current ?:-)

Not to mention that it doesn't even zero-cross detect ;-)

...Jim Thompson

You refer to Electronics Design Magazine, I assume,

"The Authority on Emerging Technologies for Design Solutions"

which deconstructs to

"You're Too Dumb to Design it Yourself so Buy the Stuff We Advertise."

Their articles always start with a journalism-ese hooker line like "Current measurements are used in a variety of equipment for control or safety functions" and similar pearls of wisdom. My rule is to never read the first paragraph at all.

John