satcure circuit

Can one of you fellow members tell me how many windings i should use on the transformer of this satcure circuit. Im using 30 gauge magnet wire and a small barbell style core. Im playing with circuits for my luxeon emitter. here is the url for the circuit.web page satcure

There's been a little discussion of this in another forum here: "1 transistor step-up-Need help !!" where I've told what I know so far. In a nut shell, the number of turns controls frequency, and I've had a circuit to drive one ordinary LED work with 4 to 19 turns on the toroid I'm using.

No one's adequately explained how the satcure/one-transistor circuit works ... so I'm asking now. How the heck does this thing work?

-XCN-

Well a step up circut works like this...

You have a transformer which is really just 2 coils on a piece of iron. One coil is smaller than the other. The smaller coil has electricity going through it which "hops" over to the larger coil. Voltage is increased but not current.

I don't know how you could fit one of these in something small like an Arc though, so I think a satcure circut probably works on the same principle...but on a much smaller circut, if not correct me and teach us both

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Saaby:
Well a step up circut works like this...

You have a transformer which is really just 2 coils on a piece of iron. One coil is smaller than the other. The smaller coil has electricity going through it which "hops" over to the larger coil. Voltage is increased but not current.

I don't know how you could fit one of these in something small like an Arc though, so I think a satcure circut probably works on the same principle...but on a much smaller circut, if not correct me and teach us both

<HR></BLOCKQUOTE>

My (lack of) understanding is that step-up and step-down transformers require AC to work. This is why you have oscillators and rectifiers in DC-DC converter circuits.

The Satcure circuit does 3 weird things with its transformer:

1.) It runs DC through it, not AC.
2.) It physically connects the primary and secondary windings.
3.)The number of turns is the *same* for both primary and secondary -- but they're wound closely together on a toroidal core.

My guess is that the modified transformer is somehow acting as an oscillator, either on its own or in combination with something else in the circuit. I wanted to try to sim the thing in Linear SwitcherCAD III to get a better understanding, but that went absolutely nowhere.

As for size, that's not a problem at all. You just have to find a small enough core with sufficient permeability, and wind it yourself. (I think that's what the symbol in the Satcure circuit is indicating for the core?)

-XCN-

Did a bit more searching, and dug up some more Web pages with the Satcure. The circuit seems to have originated as an article in the November 1999 issue of "Everyday Practical Electronics", and was written by Z. Kaparnik. I guess it's known as a "Satcure" circuit now since those guys started selling it as a kit.

I haven't been able to find an adequate explanation for the whole circuit yet, but the gist seems to be that the modified transformer does function as an oscillator, with the wiring set up so that the primary and secondary windings are out of phase with each other. It apparently produces pulsed high voltages (Satcure says ~30V without LED) which are "clamped down" when the LED is connected to the transistor and ground.

The Satcure versions omit the Schottky diode and output capacitor; I think those are used to smooth out the output current, but not sure.

So basically, it's a step-up circuit with unregulated, pulsed output ... I think.

Links:
http://edusite10.tripod.com/led3/onetran/single_tran.html http://www.emanator.demon.co.uk/bigclive/joule.htm http://www.netcentral.co.uk/satcure/design/microtor.htm

-XCN-

Here's my best guess:

Start with the switching mode of a transistor; if you bring the base voltage close to the emitter's voltage the transistor goes to cutoff; only a little leakage current will flow. Bring the base voltage closer to the collector's voltage, and the transistor goes into saturation, and the transistor will only drop a small fraction of a volt and pass a lot of current.

In the satucure circuit, the primary of the transformer is connected to the collector of the transformer and the secondary is connected to the base.

When the transistor is conducting, current will flow thru the primary. As long as the field in the inductor is expanding, a current will be generated in the secondary which pushes the base voltage closer to the collector voltage, quicky putting the transistor into saturation and maximising the current thru the coil.

When the inductor is saturated, the field ceases to expand and so the voltage that was being generated in the secondary stops; the voltage to the base is not held so high, and the transistor drops out of saturation. This reduces the current thru the primary, and the inductor's field starts to collapse. The collapsing field generates a voltage in the primary, which boosts the voltage to the LED. The collapsing field also generates a voltage in the secondary, but this time the reverse of the voltage generated earlier; this time the generated voltage pushes the transistor's base toward the emmitter's voltage and further reduces the current thru the transistor, reducing current thru the coil, collapsing the field faster and pushing the transistor into cutoff until the field has totally collapsed.

At this point the base is no longer being driven toward the emitter voltage, the transistor comes out of cuttoff, and current from the emitter again begins to flow thru the collector and coil. The field begins to build, and we are back to the initial condidtion.

The inductance of the primary coil slows the rise and fall of the current, and is the primary determinant of the frequency at which the circuit will oscillate.

Anyone care to verify or refute?

This is perhaps my favorite circuit. It will even power a LS enough for a good night light. Here are a few of my smallest ones. I made one to fit inside a straw also.
The one on the top is the last one I made...the one on the bottom is the first. I used a dollop of epoxy to seal it all up.

Yes, it's small, and I havn't fould any circuit that will operate at lower voltages. Too bad it isn't regulated.

I've used from 4 to 19 turns on small toroids or double beads, driven by a 2N4401 or 2N2222 transistor.

Any ideas on how to optimise it?

What core, turns, and transistors are you using?

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Evan:
Yes, it's small, and I havn't fould any circuit that will operate at lower voltages. Too bad it isn't regulated.

I've used from 4 to 19 turns on small toroids or double beads, driven by a 2N4401 or 2N2222 transistor.

Any ideas on how to optimise it?

What core, turns, and transistors are you using?<HR></BLOCKQUOTE>

Sorry...
No idea how to make it better.
I ordered 6 or so of every core that was in the Hosfelt catalog. 2or so were unusable. The rest I tried using different wire sizes etc. Basically, I got the same results....or no results.

I did find a way to help getting the wires into the core. If you take the smallest nylon wire tie and trim it, and use the tip to "open up" the turns, it will go much easier.

I am not an engineeer, but a tinkerer...so my methods may not have been the most scientific. I measured the total current used by the circuit and then measured the total current going through the led.

I got the lowest total current and highest led current after all that screwing around, by the basic Satcure circuit. All parts are available from Hosfelt. They have a core ( the size of a Tic-Tac ) and any basic transistor seemed to work just fine. I paid over a buck for a super high efficiency one and it performed just as well as the 5 cent one from Hosfelt.

Good Luck!

I have a D cell and run a night light for about 2 months or more...always on. It lights the bathroom .I have 3 women in the house and I get beat if I miss.. I converted one of those 1 D cell strobe lights. I basically gutted the head and had enough room for everything in it. It is very easy to replace the battery and it has a mercury switch and it totally waterproof if I take it camping.

Good luck.