interesting DC-DC converter

The toroidal core IS the "iron", on fast transitions created by the Q1+Q2 flip-flop it has much better eficiency then the traditional iron plates design. For air core you need frequencies to match, changing most of other components to respond to RF design. Reducing number of components is easy if you start designing from zero.

Have fun

Stanislaw Slack user from Ulladulla.

Okie dokie, I think I might be in over my head on this one for designing from zero.

Most of the DC-DC converter schematics I've seen on the web seem to be simple square-wave generators, which then are fed into a step-up transformer. (Which I'd like to eliminate, in favor of a simple inductor.)

Any suggestions on literature I can read to gain a better understanding of the mechanics of DC-DC converters? ;)

FWIW, I *have* taken a basic Circuits class at the university (it was a requirement for graduating from the College of Engineering) but it mostly covered LC, LRC circuits, Norton, Thevenin, etc. Nothing too exciting. ;)

Get the data sheet for the MC34063A DC to DC converter. It covers the basics very well. Brian

Not really. That's pretty light as switchers go.

You might consider using a switcher-on-a-chip like UC3843. That puts oscillator and feedback stuff on chip. But it doesn't help understanding any.

You need to consider the circuit in sections. First of all, ignore resistors, they aren't parts. ;) There's a two transistor multivibrator on the left; farther right the output transistor which drives the inductor; a diode which rectifies the flyback pulse from the inductor, and a filter capacitor to store the energy in; and a zener diode and another transistor to throttle power, to keep voltage more or less constant.

The problem is, the throttle transistor pulls down the drive transistor gradually. When you want efficient, you want solid on or off. 1/2 on, or

In a switcher, you don't want to change energy by changing conduction. That's horrible. You want to change it by the time you spend "charging" the inductor. Charge it for shorter and it doesn't have as much energy, simple enough.

Ferrite. Iron would get pretty well toasty, unless you run it really slow (audio frequency).

Tim

Start with the National LM3478 data sheet. Then read up on the Unitrode app notes (now TI). Those are most excellent switcher tutorials. If you can find the old "Unitrode IC Data Book" that would be even better.

I also found university a bit on the "non-exciting" side. Most of the stuff I use these days was learned from data sheets and application notes. And, of course, from trying things out. Just play it safe with switchers, put a fuse or big light bulb in front and don't touch stuff with your bare hands. I also wear safety goggles since these things can put on quite a pyrotechnic show when something goes wrong. TO-3 caps becoming airborne and all that.

Regards, Joerg

snipped-for-privacy@yahoo.com wrote: (snip)

You might read this tutorial:

I think a better way for you to go would be by using an integrated switching supply controller. Lots more complexity, inside, but simpler and more complete from your perspective.

Luhan Monat (luhanxmonat-at-yahoo^dot^com)

Actually, I was hoping to convert 12VDC (from a jumpstart battery I have) to 18VDC at about 2-3 amps. (That's why I wanted to avoid a transformer - that would be a big one. ;)

Reason why I'd want to, apart from learning: well, I bought an 18V cordless electric drill (on sale at Harbor Freight: $20) then I realized it has a NiCd battery. From my experience with NiCd batteries, they only last a few years at most, then die. I am planning to power the drill with my jumpstart battery when that happens.

About a decade ago, I remember building a DC-DC converter from Forrest Mims' Engineering Handbook. I had hoped to build a stun-gun from it.

snipped-for-privacy@yahoo.com wrote: > the mechanics of DC-DC converters? ;)

If you go to some junk-shop they still may have the ancient DC motor driving a DC generator. (the mechanical solution) All newer ones rely on a chopper (mechanical or electronic) to convert the DC into transitional shape which can be converted to any value by inductive transformers (and rectified back to DC).

HTH

Stanislaw Slack user from Ulladulla

Hey, if you want a good answer here, Ask the Real Question. In your case anybody could have told you to just plug straight into the 12 volts. That will run at about half power - still plenty for most any emergencies.

Luhan Monat (luhanxmonat-at-yahoo^dot^com)

Would a DC-DC converter still work though for an 18VDC electric drill? Or would the motor fry the converter electronics?

That depends entirely on your conducted noise mitigation skills :-)

Regards, Joerg

Would a capacitor in parallel with the load be sufficient? ;)

Depends on the quality of the cap and your skills in placing it 8-D

I have run big DC brush motors off switchers and never had any problems. Just imagine: A huge engine in a locomotive, nowadays tied to an electronic frequency/power converter to enable braking energy feedback and stuff like that. All hooked up to an overhead wire that makes contact most of the time, sometime only a little, sometimes shoots off big fat blue sparks, gets hit by lightning, bzzzt. Yet these things run for years without trouble.

Regards, Joerg