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Simple flyback driver Help please!

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quicksilver

Tue Apr 27 2010, 05:46PM

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

Niykon:

Good advice re: out of phase coil windings. SWITCH the leads from one to the other (from the "top" of the coil to the bottom") & make your feedback and primary turning in the same direction.

*--------# *--------%
*--------% = *--------#

Additionally, using a commercial battery charger as a PS is not the best idea as they not made for that purpose generally. A "wall wart" transformer may get you a clean, stable 12vdc; some laptop wall chargers are 19Vdc w/ 3A.

One other thing....I was looking at your schematic.....IF you are using low wattage resistors; you're gonna' have troubles. Use at least 5W. That schematic shows 1/2 W on one & I'll tell you from experience, those puppies will smoke fast unless you're putting VERY low current through them.

Antonio

Wed Apr 28 2010, 01:44AM

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

I have some drivers here:

They were intended to power "lifters", and not for producing arcs. I tried to make them efficient. I have some other power supplies more complicated than these, but not necessarily better. In all cases I used the internal primary coil and high-voltage drivers.

quicksilver

Wed Apr 28 2010, 04:28PM

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

This is a VERY common simplistic design, used for a SGTC or whatever. I have had some luck with it before I started experimenting w/ 555's. It's very flexible - but no long runs. Hold time periods to under 30sec of activity & use a large heat sink on the transistor.

quicksilver

Wed Apr 28 2010, 04:36PM

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

Antonio wrote ...

........To switch at tens of kHz, obtaining the full power that the transformer can handle, you need a higher voltage power supply, possibly more than 100 V (this is what is used in TVs and monitors). With an external primary you essentially trade less voltage for more current, and your power supply must be able to handle it.

Antonio:
Could you go into some detail on using higher voltages (100) w/ a flyback. I have never tried going up that high & wondered what you did, what your results were, & the specific current used, etc

Thanks

Antonio

Thu Apr 29 2010, 12:41AM

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

quicksilver wrote ...

Antonio:
Could you go into some detail on using higher voltages (100) w/ a flyback. I have never tried going up that high & wondered what you did, what your results were, & the specific current used, etc
Thanks

The normal primary coil is usually designed to work with voltages of that order. In CRT monitors the circuit is frequently quite complicated, with a switching power supply producing, maybe, 160 V, and another switching regulator reducing and regulating it for the flyback circuit. This is necessary because the flyback driving frequency is the same of the horizontal scan, that can vary depending on the screen resolution settings. A bipolar transistor rated at 1500 V, 10 A or little less, is used to drive the transformer, with a fast high-voltage diode and a high-voltage capacitor used for voltage limitation and energy recovery, as in the schematics in the link that I posted above. The average current required is not high, simplifying the power supply. In my schematics there is no regulation of voltage or current, and the maximum input voltage is of just 50 V. This requires operation at a few kHz only, due to the high inductance of the normal primary coil.

quicksilver

Fri Apr 30 2010, 02:44PM

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

Antonio:
Thank you: I will try your design, it looks like I can do it. Please 2 more questions.....
In your top schematic, which is the highest power level transistor? I was hunting for the parts but could not find BU2520. - If you could get any parts you wanted, do you know a specific transistor you would use?

In the bottom schematic you have 4 capacitors / switches to ground. This is to change frequency?

Niykon

Fri Apr 30 2010, 08:45PM

Registered Member #2826 Joined: Sun Apr 25 2010, 08:21PM
Location:
Posts: 6

Well guys, I must be a complete noob. I tried getting a neon sign transformer to do my ladder with. Its a little on the low side, at 9500v 30mA, but I ought to be able to at least get a spark out of it!

Anyways, its 12-15v input @ 5A max. Im not getting anything. Ideas here?

dwarnecke11

Fri Apr 30 2010, 09:14PM

Registered Member #2833 Joined: Thu Apr 29 2010, 02:54AM
Location:
Posts: 8

I used the 555-MOSFET arrangement with a 7812 governing the 555 and 30V across the MOSFET. Here is the result:

Nothing fancy. I'm sure a ZVS would be superior but that design requires some specialized diodes, caps etc I don't have on hand.

Antonio

Sat May 01 2010, 05:49PM

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

quicksilver wrote ...

Antonio:
Thank you: I will try your design, it looks like I can do it. Please 2 more questions.....
In your top schematic, which is the highest power level transistor? I was hunting for the parts but could not find BU2520. - If you could get any parts you wanted, do you know a specific transistor you would use?

In the bottom schematic you have 4 capacitors / switches to ground. This is to change frequency?

The transistors were simply selected among several that I took from discarded monitors. They are usually rated at 1500 V, 6 to 10 A. Look for one with high current gain (13 for the BU2520), or the driving circuit will have to be quite powerful. Yes, the switches and capacitors select the frequency. In that configuration the resistor in the 555 oscillator controls the duty cycle, not the frequency. Note that these drivers were not designed to produce arcs, at least not for long time. A Jacob's ladder requires a series resistor for current limitation, it the driver doesn't limit it.

Niykon

Sat May 01 2010, 08:28PM

Registered Member #2826 Joined: Sun Apr 25 2010, 08:21PM
Location:
Posts: 6

So..... any idea about this nst? I checked the fuse, its good......

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