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Improved single transistor flyback driver

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Antonio

Sun May 25 2008, 11:18PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

To determine the voltage precisely, produce sparks between balls. The spark length between points depends on many details, and is easily 3 times longer.
This is 20 kV:

A good formula for the voltage for a spark between two identical balls is:

V=E*4*d/(d/R+1+sqrt((d/R+1)^2+8))

E=30000 V/cm
d=spark length (cm)
R=ball radius (cm)
(sqrt=square root)

1 cm sparks between balls with 2 cm radius gives 25523 V

Spedy

Wed May 28 2008, 02:42AM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Dr. Monsterarc wrote ...

Here is the promised run with a DC flyback

Approx. 40kV. I used: 390R/2W, 10(!)R/6W, 8 pri. turns, 3 feedback turns, 0.56uF cap, KD606 transistor (made by "Tesla", long discontinued, but it's the best transistor for the single transistor driver I ever had...) gets just little warm after short runs.

I'll try to remove some primary turns and set the operating point so I get more kV out with the same power...

So you mean the 390R/2W at the 'top' of the schem. and the 10R/6W at the bottom, right?

Shaun

Wed May 28 2008, 03:55AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Antonio, where on earth did you find that formula!? That's a nice one; it sure takes things further than just 1.1kv/mm like i usually use to "measure" voltage.

I think it deserves this though, for ease of understanding:

Dr. Dark Current

Wed May 28 2008, 06:09AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Spedy wrote ...

So you mean the 390R/2W at the 'top' of the schem. and the 10R/6W at the bottom, right?

yeah

---
what I found out: More feedback turns=more power (but not necesarilly more voltage). Decreasing the value of bottom resistor results in more power and voltage, but the resistor WILL get very hot if you get it too small. The top resistor has minimal effect on performance, so it is best to use the highest value that allows for reliable start-up.
Bigger capacitors tend to produce hotter arcs possibly with decreased output voltage.

quicksilver

Wed May 28 2008, 02:27PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Dr. Monsterarc wrote ...

Decreasing the value of bottom resistor results in more power and voltage, but the resistor WILL get very hot if you get it too small. The top resistor has minimal effect on performance, so it is best to use the highest value that allows for reliable start-up.
Bigger capacitors tend to produce hotter arcs possibly with decreased output voltage.

You bring up a very interesting point from what I am just studying. When I was looking at the circuit I believe those resistors to be functioning in parallel even though they exist in a series of two (one after another). If I'm correct and they are functioning in parallel, their collective value will be lower than the lowest one of the two.

Example: We have two resistors, a 22 ohm & a 470 which = 492ohm but the actual resistance would be 21 ohm if they are used as parallel with our circuit. But if we didn't have a 22 & 470 but a 92 & a 400 ohm we would have 75.1 total resistance. I tried playing with the values and that gave me the idea that they were functioning in parallel. If I'm right we could use two resistors & depending upon the values of each those choices would determine the functionality. So this concept playing itself out to the fullest - if we had a 600 & a 20 ohm, our total resistance would be 19.3 ohms....even less than the 470 & 22 original design.

{I also was wondering what you meant by the term "big" in capacitors; voltage or storage...? As I'd like to experiment with that.}

Spedy

Thu May 29 2008, 12:10AM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Hmm, this could present a problem for me. What if I paralleled a ton of resistors of the same value to get a higher wattage, would the resistance change? Ex: 10x 10ohms in parallel would = less than 10ohms?

Tesladownunder

Thu May 29 2008, 12:56AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

This circuit has been around for a long time. I got my circuit from Sam Barros' site and made it up in 2002. Draws 3 A at 20V with 2N3055 for 1/2 inch spark.

TDU

Antonio

Thu May 29 2008, 01:14AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Shaun wrote ...

Antonio, where on earth did you find that formula!? That's a nice one; it sure takes things further than just 1.1kv/mm like i usually use to "measure" voltage.

I think it deserves this though, for ease of understanding:

The formula comes from this document ("North report"):

It is said there that the formula is exact, but it isn't. It is a good approximation, however. The exact expression has an infinite series.

flannelhead

Mon Jun 16 2008, 05:43AM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

I made a 555 based single MOSFET driver and started with a 440nF cap across the FET. The arc started at 5mm and stretched to 25mm. Then I removed 220nF from the capacitance and the arcs started at 20mm and drawed to 50mm! So tuning is very important.

coffeetable

Wed Oct 21 2009, 06:18PM

Registered Member #2443 Joined: Wed Oct 21 2009, 06:08PM
Location:
Posts: 1

Apologies for the thread necromancy, but I figured it was better than posting an all-new thread just for my question;

I'm a newbie. I built the 2n3055 circuit on the wiki, it worked, but they were right to say it leaves you wanting more. So I tried to build this one, with the materials to hand.

The materials at hand are a 2SD1555 transistor (built in damper diode, ~5V threshold voltage) and a 12V power supply. And it doesn't work.

My suspicion is that I'm not delivering enough voltage to turn the transistor on, but I've got no idea how to modify the circuit to fix this. Can anyone help?

(explainations of why the changes you suggest would fix it would be appreciated as well, so that I can actually start to understand what I'm building)

Thanks

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