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NNTP-Posting-Date: Tue, 26 Nov 2002 11:12:59 -0600
From: email@example.com (John Fields)
Subject: Re: Electroluminescent displays
Date: Tue, 26 Nov 2002 15:54:18 GMT
Organization: Austin Instruments, Inc.
References: <3DE11C25.6123DC38@chariot.net.au> <firstname.lastname@example.org> <8cBE9.email@example.com>
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On Mon, 25 Nov 2002 21:42:32 -0500, "red rover"
>I use to design high-end EL display circuits (not backlights)
>for military use. Primarily US Army helicopters (and even Air Force 1).
>I have never seen visible color shift.
Perhaps because the driving frequency was fixed? The lamps I was
talking about are the garden-variety green lamps used in
nightlights, exit lights, house number signs, etc., which glow green
with 120V 60Hz across them. It's easy to see the color shift, just
get a "Limelight" from Home Depot, hook it to the 70.7V winding of a
line matching transformer, hook one of the secondaries to one of the
speaker outputs of your stereo and drive the corresponding aux input
with an audio oscillator. Fun.
> I do recall there use
>to be DC units but everything had gone AC by the mid 80s.
I've never seen nor heard of DC EL. What made them work?
>The AC voltage required was a trapezoid with around 210V dwell
>as I recall. Brightness was
>controlled by varying duty-cycle, frame-rate and voltage.
The only way I've controlled brightness was by varying the voltage
once the frequency was set.
>had a choice of Green or Amber. Amber was much brighter but annoyingly
>close to the filter wavelength for the Night Vision Goggles.
>For low voltage battery powered DC backlights (like the Timex
>Indiglo watches) I recall that one of the small IC shops made
>a special chip for this. I'm pretty sure it was Sipex.
It's low-voltage battery powered, but it's still an AC driven
device. That's what the chip is for; it's an inverter which boosts
the watch battery voltage up to around 30V, as I recall. Dim, but
bright enough to read the LCD at night.
Professional circuit designer
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