inverting dc-dc converter circuit

Incredible.

Why a 555 with a trivial diode-capacitor voltage multiplier won't work?

VLV

It's incredible that you think it might. Stick to digital.

John

You mean this doesn't work:

Diode forward drops would be an issue if you really need -30 and are trying to use a doubler circuit. Otherwise, for the benefit of the rest of us, why wouldn't it work?

Sylvia.

Well, it wouldn't even produce -15v from +15v, let alone -30v.

Sylvia.

At least one more cap to keep droop below 10% ppk. 25uF

The switched caps would have to be 5 or 10x multiples of this to maintain anywhere near 30V after the transfer.

With half the energy transfer lost in switching, thats 120mA drawn from the 15V rail.

Not small anymore.

There are quieter conversion methods than flyback or switched caps.

Harpo was mute.

RL

What make SSRs "fairly soft switching edges"? May be better to make a sin generator and a transformer?

The PV-powered gate drivers are very weak, so the switching edges are slow, far slower than a 555's. And the fets go from resistive to constant-current at higher voltage drops, which further softens things up.

And SSRs are fast-break, slow-make, so there's no shoot-through.

John

There's no point to trying it. It's obvious that it wouldn't meet my requirements. Stick to digital.

John

You can get opto-MOSFET switches as SSRs

If you are careful to not have the source legs be the ones that move, you can use a capacitively coupled gate drive on a low Vth MOSFET and save on the current for driving the LEDs.

If you use a sine wave to drive the MOSFETs, you can have their switching be very soft and hence low noise.

An N channel and P channel MOSFET pair can switch one end of a capacitor from +15 to ground.

An N channel and P channel MOSFET pair can switch one end of a capacitor from ground to -15

An N channel and P channel MOSFET pair can switch one end of a capacitor from -15 to ground.

An N channel and P channel MOSFET pair can switch one end of a capacitor from -30 to -15

It looks like 8 MOSFETs plus two working capacitors would do it.

Larkin and Obama are out of the same mold... mediocre talent, yet excessive ego ;-) ...Jim Thompson

If you still have this circuit handy, please re-post.

don

How 'bout a 48V power supply and define ground where you want it? Or do you need most of the 'poop' at +15 Volts?

George H.

The 555 would only swing about 13 volts p-p. Then you get to start in on diode drops.

The 555 edges are ballpark 100 ns, noisy.

John

Here it is:

ftp://jjlarkin.lmi.net/Inverter.jpg

John

Sure, it needs an output cap.

I'd just use huge aluminum electrolytics. 1000 uF caps would be no problem.

No. A charge pump like this can approach 100% efficiency.

The nice thing about the Groucho circuit is how slowly it runs, ballpark 400 Hz, with soft switching edges. And no magnetics.

John

Two years ago I did the electronics for a super noise-sensitive fiberoptics project. Late in the game a spec change came along (don't they always?) and now we needed +40VDC and +210VDC. There was only 12VDC available to make it from. So I did two homebrew converters, MIC4421's driving FETs and I babied the shoot-through a bit. The 40V got one of those Cooper Versa Pac transformers and the 210V an ordinary CCFL transformer. The rectifiers were well muffled with the usual inductors.

Not one wee whiff of noise. Ok, I had it on a PLL but even when I unclutched that there was no noise. I love magnetics.

Cool :-)

Whereas Jim's egomania is justified by his stellar reputation amongst integrated circuit designers? Bob Widlar, Barry Gilbert and Hans Camenzind recognised him as comparable talent? Had every actually heard of him?

-- Bill Sloman, Nijmegen

How about a couple of LTC1144s?