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PICList Thread
'EL LCD Backlight'
1998\02\16@220909 by Adi

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Hi!

I am experimenting with LCD display modules most of which have EL
backlit stuff on them. Are there any quick and dirty ways of
illuminating those? If read those things need a fairly high AC
voltage ~150ppVAC @ 300kHz or so but that's about all I know about
it...

Thanks,
Adi

1998\02\17@065943 by Andy Kunz

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>I am experimenting with LCD display modules most of which have EL
>backlit stuff on them. Are there any quick and dirty ways of
>illuminating those? If read those things need a fairly high AC
>voltage ~150ppVAC @ 300kHz or so but that's about all I know about
>it...

Adi,

There are several companies which make "inverters" which will convert a
5VDC or 12VDC into the requisite xxKVAC.  Check with the mfg of the LCD
panel you use for their recommendations.  I've always been satisfied doing
it that way.

Andy


==================================================================
                   Andy Kunz - Montana Design
==================================================================

1998\02\17@072004 by Keith Howell

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Adi wrote:
> I read those things need a fairly high AC voltage ~150ppVAC @ 300kHzNot all.
I have some that are DC and run off a 9V battery. I think the problem is
that water vapour (and DC?) shortens the lamp life.

If electrodes don't enter the hermetically sealed enclosure, then this
reduces moisture intrusion.
The current then has to be induced by AC, because with the electrodes
either side it forms a lowish value capacitor.
The high voltage is needed to get appreciable current flow.

>From what I've seen, HV AC ones get used in stuff like laptops where a
long life and high brightness is needed.
The LV DC ones get used in things like mobile phones which are not on
for extended periods.

I have a bagfull (c. 20?) of the latter, awaiting a use.

I confess I may be mistaken on these points.

I did some designs for driving HVAC CCFL for industrial PCs with flat
panel displays. You can buy ready-made modules cheaply, but you can get
driver chips designed for the job from Maxim.

1998\02\17@081906 by wwl

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On Mon, 16 Feb 1998 20:56:03 +0000, you wrote:

>Hi!
>
>I am experimenting with LCD display modules most of which have EL
>backlit stuff on them. Are there any quick and dirty ways of
>illuminating those? If read those things need a fairly high AC
>voltage ~150ppVAC @ 300kHz or so but that's about all I know about
>it...
lose the K in the frequency - it's usually 150-300Hz. Sipex and Rohm
do controller chips that just need an inductor to run small EL panels.
TDX and probably others do ready-made inverter modules

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1998\02\17@124749 by Bob Blick

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The cheapest and dirtiest way to do it is with AC out of the wall, either
110 or 220 volts. Use a resistor to limit the current! I do not remember
the values I have used, but 100k ohms when running from 110 volts will not
get you into any trouble, and decrease the resistor to increase brightness
to the point that the backlighting burns out, then increase the resistir
value and start with a new backlight module :-) I seem to recall 1k ohms
was the value at which death of the module started.

-bob

On Mon, 16 Feb 1998, Adi wrote:

{Quote hidden}

1998\02\17@160202 by Daniel Dourneau

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At 20:56 16/02/98 +0000, you wrote:

>I am experimenting with LCD display modules most of which have EL
>backlit stuff on them. Are there any quick and dirty ways of
>illuminating those? If read those things need a fairly high AC
>voltage ~150ppVAC @ 300kHz or so but that's about all I know about
>it...

Well 300 Hz should be just about enough.
To get you started you can buy ready made inverters for these things (TDK
in Japan makes them) or contact Sipex; they make ICs dedicated to these
applications. Actual diagram and component value may change according to
type of EL film, but it should be OK for one off; it would be a different
matter if you want to start mass production. There tuning of EL lamp and
inverter becomes critical for long life of the lamp. Durel and Seiko
Precision also carry EL lamps and drivers, Supertex also makes ICs for
drivers.
I wish you successful experiments; let us know.
Daniel Dourneau

1998\02\17@172543 by Gary T. Pepper

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At 11:05 PM 2/17/1998 +0100, you wrote:
>At 20:56 16/02/98 +0000, you wrote:
>
>>I am experimenting with LCD display modules most of which have EL
>>backlit stuff on them. Are there any quick and dirty ways of
>>illuminating those? If read those things need a fairly high AC
>>voltage ~150ppVAC @ 300kHz or so but that's about all I know about
>>it...
>

Hi All,

B.G. Micro has a flourescent inverter board for fluorescent backlight
panels with the following specs

input : 12 VDC
output: 1000 volts (a.c.) 200 kHz  (note: their catalog says kHz, not Hz)
price:  $2.95 (US)

I haven't tried one of these, but am thinking of purchasing some to test out.
NOTE:  I have no affiliation with B.G. Micro - I'm only a satisfied customer!

Regards,
Gary Pepper

e-mail: .....gpepperKILLspamspam@spam@capitalnet.com


B.G. Micro:
http://www.bgmicro.com

1998\02\17@203238 by Herbert Graf

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> -----Original Message-----
> From: pic microcontroller discussion list
> [PICLISTspamKILLspamMITVMA.MIT.EDU]On Behalf Of Adi
> Sent: February 16, 1998 15:56
> To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
> Subject: EL LCD Backlight
>
>
> Hi!
>
> I am experimenting with LCD display modules most of which have EL
> backlit stuff on them. Are there any quick and dirty ways of
> illuminating those? If read those things need a fairly high AC
> voltage ~150ppVAC @ 300kHz or so but that's about all I know about
> it...

       You've got it, although most are quite varying, most will work at only 7
0
or 80V, and at a lower frequency, even as low as a few thousand hertz. TTYL

1998\02\17@213309 by William Chops Westfield

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   >>I am experimenting with LCD display modules most of which have EL
   >>backlit stuff on them. Are there any quick and dirty ways of
   >>illuminating those? If read those things need a fairly high AC
   >>voltage ~150ppVAC @ 300kHz or so but that's about all I know about
   >>it...

   B.G. Micro has a flourescent inverter board for fluorescent backlight
   panels with the following specs


Ack!  PHht!  Fluorescent backlights (CCFL) are NOT NOT NOT the same as
electroluminescent film (EL) backlights!!!!

A typical CCFL is more or less a fluorescent lightbulb, perhaps in a weird
shape.  They take high voltage current-limitted AC, with an even higher
voltage start condition.  Usually the current limitting is done via an
inductor (not dissimilar from a household fluorescent light ballast), and
high frequencies are used to keep the size of inductors relatively small.
I believe CCFLs are uses in almost all laptop-like applications, an EL
backlight simply isn't bright enough.  Linear Technologies has some really
good app notes on voltage converters for CCFL backlights.

A typical EL backlight is a phosphor inside a film capacitor, where the
phosphor picks up some energy from the electric field and emits light.
They are only moderate voltage (80-200V) at relatively low frequencies
(60-200Hz.)  A typical EL driver has a whopping big tiny inductor (25
MILLI-henries worth of very fine wire on a surface mount core) and work by
sending short pulses through thr coil, generating high volatge back emf by
virtue of dI/dt.  "Indiglo" watches and most palmtops use EL backlights,
and converters are available that run off a single cell.  I think EL
displays are very efficient except for the converters.  Supertex and Sipex
make EL driver chips and have good info on their web sites.

BillW

1998\02\18@004535 by Adi

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My understanding is that the little flat pack that's supposed to glow
under a 2x20 LCD is an EL backlight...?? I'll check out Supertex and
see what they have... Thanks!

Adi

> Ack!  PHht!  Fluorescent backlights (CCFL) are NOT NOT NOT the same as
> electroluminescent film (EL) backlights!!!!

1998\02\18@004541 by Adi

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Now that's a pretty interesting idea! Need to use an isolation
transformer, though. I am looking for a simple converter I could run
of a battery. I looked at SIPEX chips but I didn't feel like sourcing
them for just a couple of pieces plus they're SOIC only for all I can
see.

> The cheapest and dirtiest way to do it is with AC out of the wall, either
> 110 or 220 volts. Use a resistor to limit the current! I do not remember
> the values I have used, but 100k ohms when running from 110 volts will not
> get you into any trouble, and decrease the resistor to increase brightness
> to the point that the backlighting burns out, then increase the resistir
> value and start with a new backlight module :-) I seem to recall 1k ohms
> was the value at which death of the module started.

1998\02\18@125627 by Bob Blick

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On Tue, 17 Feb 1998, William Chops Westfield wrote:
>
>
> Ack!  PHht!

Was that William "Bill The Cat" Westfield speaking there? :-)

Nicely put!

-bob

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