Zener turn-on question

Charge pumps are cool; unfortunately when you're going for low-cost/low-power implementations that have to accommodate a varying input voltage I don't think they're as practical a solution as a traditional (magnetics-using) boost. Efficiency of a fixed-ratio charge pump is pretty good at low input voltages but then drops off bad as the input becomes a larger fraction of the output.

It's possible to do better with fractional-ratio pumps but probably best to buy an off-the-shelf IC for that.

Switching to a lower (~30 ohm) DCR inductor and swapping the 100k timing resistor for 47k and I managed to pull ~5 mA from my variation on the original design. The "switching node" square wave looks very crisp and the boost output on Vdd looks remarkably clean for such a goofy circuit that's being driven "backwards"

A variable-ratio pump is possible, but complex.

We knew a young lady who wanted a green Porsche, so had it air-freighted in from Germany. Then she wanted a da-da-la horn to make her entrance at a picnic or something, but the Porsche was 6 volts and the only horn available was 12. So we got a 6-volt motorcycle battery and a relay and made a 2:1 step-up charge pump.

That kind of circuit isn't worth it anymore. Looks like a holdover from the 1980s when people were always looking to cobble a kluge together out of ex cess on-board parts. This doesn't make any sense anymore with the vast sele ction of self-contained parts. And the "micropower" claim is bull, since th e zener needs at least a few mA continuous, which at 12V, makes it a "milli power" circuit.

There once was a lady who had a green Porsche, Who always announced her arrival with force, "Oh heavens no, My voltage is low!" So hawk her a charge pump, of course.

Good, but we did it for free, so change hawk to make.

When holdovers from the 1980s is what I'm looking for this is definitely the place to be!

This was a while ago, one gathers. ;)

Sounds a bit like the old lady who swallowed a fly....

I know a young lady/ who wanted a Porsh(*)/....

Cheers

Phil Hobbs

(*) one syllable

I assume the relay just put both batteries in series for the horn and parallel for charging. But why call that a charge pump? I thought a charge pump was a switched cap thing. (Or maybe I'm mis-understanding.)

George H.

Yes, I was a college student. Her daddy owned a few hundred tugboats.

For a mild-mannered circuit designer, I've seen a lot of strange stuff.

A battery is just a big capacitor.

Well done!

Tim

Geez, that's a lot of run-on assuming!

I didn't need power efficiency, I needed to get the best voltage boosted (but not *too* big) pulse possible in a tiny space.

Did you look at that LM385-ADJ?

Cheers, James Arthur

Yeah, but the analog switches need a Vdd >= Vout to work, right?

The neat thing about the long-lost CMOS gate-based multiplier was that it bootstrapped its own Vdd.

YouTube has some pretty impressive Marx generators. Even some non-political ones :-).

Cheers, James

I'm glad it worked for you, but I was talking about _my_ design problem in that paragraph. Guess I should've used "one" instead of "you're", there, if that was the source of confusion.

Yeah, I'll try it! Waiting on some to come in from Mouser.

A mux-based Marx can do that too.