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'Electroluminescent panel power controller.'
1998\11\26@084215 by Gerry Cox

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I want to design a low cost Electroluminescent panel drive (Output is 280
VAC @ 450Hz and 6Watts. Input power available is at 12V). I am considering a
PIC12C508 with 2 of the I/O pins providing an anti-phase drive (at say
100Khz) to a pair of mosfets. The mosfets are arranged to push-pull a center
tapped ferrite transformer with the center tap connected to +12V. The
secondary of the transformer will be full wave rectified and smoothed to
provide a 280VDC supply. Another output  of the 12C508 will drive a
transistor switch alternately to the 280V rail and then to 0V rail  at the
required 450Hz. This 280V square wave will be fed to the panel via a
coupling capacitor.

My problem is that I don't know where to start with selection / design of
the transformer. Can I design it myself or am I likely to find an off the
shelf item to do the job? Anyone got any leads on ferrite transformer
design?

Thanks in advance,

Gerry Cox.
Dorset U.K.

1998\11\27@151020 by wwl

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On Thu, 26 Nov 1998 12:57:52 -0000, you wrote:

>I want to design a low cost Electroluminescent panel drive (Output is 280
>VAC @ 450Hz and 6Watts. Input power available is at 12V). I am considering a
>PIC12C508 with 2 of the I/O pins providing an anti-phase drive (at say
>100Khz) to a pair of mosfets. The mosfets are arranged to push-pull a center
>tapped ferrite transformer with the center tap connected to +12V. The
>secondary of the transformer will be full wave rectified and smoothed to
>provide a 280VDC supply. Another output  of the 12C508 will drive a
>transistor switch alternately to the 280V rail and then to 0V rail  at the
>required 450Hz. This 280V square wave will be fed to the panel via a
>coupling capacitor.
Bear in mind that the panel will probably be a mostly capacitive load,
so you may need a fairly large output cap. Alternatively, an h-bridge
may be a better solution

If low cost is important (rather than efficiency or size) , have you
looked at using sine(ish)wave drive into an off-the-shelf mains
transformer run backwards? You could probably drive the primary with a
cheap  audio power amplifier chip.

If you go the high-frequency route, a flyback type supply would be
simpler than push-pull - maxim, LT etc. have plenty of devices, some
of which can drive a transformer easily. This would require only one
switching device and HV rectifier. 100KHz is probably a bit high
unless you need to keep the size of the transformer down.
I can't remember off-hand, but you may also be able to use one of the
NS simple switcher devices.

A PIC may be slight overkill unless it;s used for other things - a
CMOS 4060 would probably do the trick (and runs off 12V)!

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