RE: Ignition Coil as a TC Transformer?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>

Hi Gary,

The pulse width is used to control the power output. With the TV flyback I
was using a duty cycle of 8% gave enough power to have an arc on the bottom
of the flyback between some unused pins. At 10% duty cycle the thing ran
flawlessly and put out an impressive amount of power.  The arc between the
pins got a little arch in it and started to get some yellow and red. At 12%
duty cycle, The arc between the pins started to dance like a Jacobs latter
if it gets stuck at a point, and the output was very good. That is the
ragged edge. At 15% duty cycle the IGBT blows. By adjusting the duty cycle
the measured output voltage varied from 2KV to 50KV.

I agree that a 555 can be used to directly drive an IGBT. Using the simplest
of circuits, like Terry's TC tuner to drive one could be the simplest driver
to build. Run it on 12V and either wind your own primary on the flyback or
drive an ignition coil.

later

deano

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Friday, March 09, 2001 3:48 PM
> To: tesla-at-pupman-dot-com
> Subject: RE: Ignition Coil as a TC Transformer?
>
>
> Original poster: "Lau, Gary by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <Gary.Lau-at-compaq-dot-com>
>
> Regarding the need to invert the 555's output to achieve a duty cycle of
> less than 50%, I can see that greater than 50% applied to the power
> transistor would result in a DC bias on the coil and excessive current
> through the transistor, but I would think that one should strive
> for exactly
> a 50% duty cycle at a suitably high frequency (?) such that the
> core doesn't
> saturate.  As noted, the usual 555 circuit will generate an output with
> greater than 50% duty cycle, but the 555 circuit that Terry used in his
> Tesla Coil tuner uses an ingenious configuration that always guarantees a
> 50% duty cycle over all frequencies.  I've not tried it but I think that
> circuit could be used to directly drive an IGBT.  See
> http://hot-streamer-dot-com/temp/TCT1.doc
>
> Gary Lau
> Waltham, MA USA
>
>
>
> The schematic is now posted at:
>
> http://hot-streamer-dot-com/temp/Schematic.gif
>
> Cheers,
>
> 	Terry
>
> At 06:47 PM 3/3/2001 -0600, you wrote:
> >Hi Matt,
> >
> >I have never used a 2n3055, but have built some flyback drivers. The last
> >one I whipped up just for fun last December uses an IGBT. The 2N3055 is a
> >popular transistor because it is cheep and universally
> available. Any good
> >high power transistor will work. The trick is to use something like a
> 2N2222
> >to drive the power transistor more or less in a Darlington configuration.
> In
> >the case of a MOSFET or IGBT which is controlled by voltage rather than
> >current and could be driven directly by the 555, a transistor like the
> >2N2222 is still needed to act as an inverter because the 555 output will
> >tend to be high longer than it is low. You really want a very
> narrow pulse
> >rather than a wide one, and inverting the output of the timer
> does that. If
> >the pulse is to wide, too much current can pop the MOSFET or IGBT.
> >
> >This circuit is designed for the development of a flyback driver and
> >includes adjustment for frequency (from approx. 18KHz to 80KHz) and pulse
> >width. I was able to get from approx. 2KV up to more than 50KV using this
> >circuit and a flyback out of an old color TV. It features an
> offline power
> >supply of around 170VDC, and a low voltage power supply for the timer and
> >switching voltage. There are no over current protection circuits in this
> >bread boarded prototype. I intend to add over current protection
> as soon as
> >I get back to the project, but am just recovering from the financial
> >disaster which is January. (Taxes, insurance, more taxes, etc.)
> I will send
> >this to you directly as an attachment. If anyone else is
> interested, email
> >me at deano-at-corridor-dot-net and I will be happy to send you a copy as well.
> >
> >later
> >
> >deano
>
>
>