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'[EE:] Inverters for Electroluminescent wire ?'
2004\08\22@211110 by William Chops Westfield

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I'm looking for some inverter designs to drive EL wire (ie
http://www.coolneon.com, http://www.coolight.com, etc)  Something more elegant
and controllable than driving the input of a commercial inverter, I
guess.  Note that the EL wire likes something like 120VRMS at 2kHz,
which is a
lot different than the 160V P-P at 400Hz that flat el panels seem to
like, which is where all the chip manufacturers (sipex, micrel, etcZ)
aim their special purpose EL drivers.

Looking at the special purpose drivers, they ALMOST look like something
where you could substitute a PIC and some high-voltage transistors.
They have a more-or-less conventional step-up switching converter that
generates about 80v, and then a HV H-bridge that drives the el-panel in
push-pull fashion to get the 160Vp-p.  I MIGHT be able to do that with
a PIC.  What are the normal limits on how high a voltage you can get
out of a step-up converter, anyway?

Alternate designs using an actual transformer would be welcome, but
it's gotta be a commonly-available or easilly-wound sort of thing.  I
assume the commercial inverters happen in big enough quantities that
they just use conventional single-transistor inverters with customer
transformers.

Thanks for any advice or suggestions...

BillW

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2004\08\22@230120 by Russell McMahon

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> I'm looking for some inverter designs to drive EL wire (ie
> http://www.coolneon.com, http://www.coolight.com, etc)  Something more elegant
> and controllable than driving the input of a commercial inverter, I
> guess.  Note that the EL wire likes something like 120VRMS at 2kHz,
> which is a
> lot different than the 160V P-P at 400Hz that flat el panels seem to
> like, which is where all the chip manufacturers (sipex, micrel, etcZ)
> aim their special purpose EL drivers.
>
> Looking at the special purpose drivers, they ALMOST look like something
> where you could substitute a PIC and some high-voltage transistors.
> They have a more-or-less conventional step-up switching converter that
> generates about 80v, and then a HV H-bridge that drives the el-panel in
> push-pull fashion to get the 160Vp-p.  I MIGHT be able to do that with
> a PIC.  What are the normal limits on how high a voltage you can get
> out of a step-up converter, anyway?

More details anon if nobody else weighs in - but they probably will.

You can get eg 80v with no great effort with a single inductor and a choke
from supply to collector of a small high voltage transistor (eg MPSA42) .
Operate from 5v or as high as is available. Turn transistor on for
appropriate period (~~ tmax = IL/V where I = peak inductor current allowed,
L = inductance, V = supply voltage) then turn off for longer than tmax x
Vin/Vout. Collector will "ring" to a large voltage. Actual max value will be
limited by LI^2 = 0.5 CV^2 so high stray capacitance can set a local limit.
80v odd should be easy enough. For eg 50 mA, 100 uH, 5v  say you get tmax =
0.050 x 100E-6 /5 ~= 1 uS on. 500 MA max = 10 uS etc.

I went to mention a single driver solution at 160v then realised the EL wire
will want AC so the full bridge makes sense. That can take as little as 6
transistors with eg 5v drive.

Let us know what you come up with.


       Russell McMahon

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2004\08\23@002242 by William Chops Westfield

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On Aug 22, 2004, at 7:47 PM, Russell McMahon wrote:

> More details anon if nobody else weighs in - but they probably will.

Ah.  I knew it left something old.  The circuit should operate from 3
to 5V or so, although some degradation at lower voltages is permitted.

>
> You can get eg 80v with no great effort with a single inductor and a
> choke from supply to collector of a small high voltage transistor (eg
> MPSA42) .
>
I want more than 80V.  Preferably, something on the order of 110V.
110VAC (which is partially what the stuff is designed to work on) is a
depressingly high number once you convert to peak-to-peak (multiply by
2*sqrt(2), right?)  Efficiancy should be pretty good, but is not of
paramount importance (however, I discovered that a camera flash
inverter will power some length of EL-wire if you intercept it at the
HVAC part.
While drawing more than an Amp from the 1.5V cell.  That's NOT
efficient enough :-)
>
> 80v odd should be easy enough. For eg 50 mA, 100 uH, 5v  say you get
> tmax = 0.050 x 100E-6 /5 ~= 1 uS on. 500 MA max = 10 uS etc.

Thanks.  That's particularly useful.  I was hoping I could tune in a
desired input current.  In theory, I understand basic electronics
including inductors.  In reality, I've never had to DO anything with
inductors, and I have about ZERO "feel" for how they work...

BillW

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2004\08\23@030446 by Russell McMahon

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> Ah.  I knew it left something old.  The circuit should operate from 3
> to 5V or so, although some degradation at lower voltages is permitted.

Peak voltage probably best limited by a clamp / shunt regulator so as long
as it rings to enough at 3V in then 5V in just wastes more.

> I want more than 80V.  Preferably, something on the order of 110V.
> 110VAC (which is partially what the stuff is designed to work on) is a
> depressingly high number once you convert to peak-to-peak (multiply by
> 2*sqrt(2), right?)

Yes and no. A square wave has RM value equal to half its peak to peak value.
A sime wave is 0.7071 x half its p-p value. Depends on response of EL wire
to voltage whether it strictly reacts this way.

More than 80 works just the same. There does come a limit due to capacitance
as mentioned before, but in most cases it will be well above this voltage.

> Efficiancy should be pretty good, but is not of
> paramount importance (however, I discovered that a camera flash
> inverter will power some length of EL-wire if you intercept it at the
> HVAC part.
> While drawing more than an Amp from the 1.5V cell.  That's NOT
> efficient enough :-)

That suggests there is quite a load. Does the EL wire have a current spec. I
thought El was quite low power. However, 1.5v x 1A = 1.5w. At say 50%
efficiency end to end that's 750 mW for light which is not a vast amount.
Again, is there



Inverters from $US5

       http://www.elwirecheap.com/powerinvertors.html

Build your own 3V inverter
He has a few minor things wrong technically but seems like a good practical
guide.
Self oscillating.
Uses two or more windings. Not to be feared.
Has quite a lot of explanation - active diagrams are good


http://www.talkingelectronics.com/Projects/Electroluminescence/LitELine04.html

Found on their electroluminescence page here.
Go down left hand column to projects etc: luminescence.

       http://www.talkingelectronics.com/

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2004\08\23@035259 by William Chops Westfield

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On Aug 22, 2004, at 11:50 PM, Russell McMahon wrote:

>> (... a camera flash inverter will power some length of EL-wire if you
>> intercept it at the HVAC part. While drawing more than an Amp from
>> the 1.5V cell.)

> That suggests there is quite a load. Does the EL wire have a current
> spec. I thought El was quite low power.

No, that's just cause the Camera inverter does a lousy job delivering
low currents.  Although, you're making be doubt my measurements...  I
may have to check again.  The inverter transformer on those has a 6
turn primary...

I did some experiments that look promising using one of those circuits
designed to drive LEDs from 1.5V:
    http://www.elecdesign.com/Articles/ArticleID/5886/5886.html

Switched the output transistor to the MPSA42 and played with assorted
inductors I have as well as the input supply voltage, while watching
things with a scope.  Had it driving a neon bulb just swell, so I'm on
the right track.  I did try to drive some elwire directly, but I think
I fried it by providing too much voltage in too short pulses.  (thus
explaining the separate inverter and EL H-bridge in conventional EL
panel inverters, I guess.  It looks like it'd be quite tough to get the
sort of waveform it likes at the same time as getting the right output
voltage.)

I guess I also need to decide to what extent I want/need to regulate
the voltage.  Sigh...

BillW

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2004\08\23@043440 by Russell McMahon

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> I fried it by providing too much voltage in too short pulses.  (thus
> explaining the separate inverter and EL H-bridge in conventional EL
> panel inverters, I guess.  It looks like it'd be quite tough to get the
> sort of waveform it likes at the same time as getting the right output
> voltage.)

I think that EL requires net no DC (I may be wrong) for long life. Can run
on DC but not for long.

> I guess I also need to decide to what extent I want/need to regulate
> the voltage.  Sigh...

Zener diodes will almost certainly be fine.

       RM

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2004\08\23@080220 by Alan B. Pearce

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>I discovered that a camera flash inverter will power
>some length of EL-wire if you intercept it at the
>HVAC part. While drawing more than an Amp from the
>1.5V cell.  That's NOT efficient enough :-)

Yeah, these converters are optimised to charge up a capacitor in a short
time :)

You could probably get good results driving the transformer push-pull from a
suitable source, without it needing to worry about the drive current.
Probably need a frequency high enough to keep the transformer from going
into saturation though, which will probably be several kHz.

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2004\08\23@081257 by Russell McMahon

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> >I discovered that a camera flash inverter will power
> >some length of EL-wire if you intercept it at the
> >HVAC part. While drawing more than an Amp from the
> >1.5V cell.  That's NOT efficient enough :-)
>
> Yeah, these converters are optimised to charge up a capacitor in a short
> time :)

Several people have commented similarly.
I know nothing about El light efficiency but, if the inverter is 50%
efficient end to end (which is quite a challenge at 1.5 volts or less at
that current level) then there is far less than a watt available for light.
If the EL wire is no more efficient than many LEDs or incandescent bulbs,
then say 3/4 of a watt is quite believable.

Consider a 3v LED at 20 mA = 60 mW.
750 mW/60 mW = about 12 LEDs. if these are modern high efficiency LEDS rated
at say 3000 - 6000 milli-Candella each then you'd get 'lots'* of light. Use
slightly older (or less efficient cheaper) ones and you could well get less
light than you see from "a length" of EL wire. Note that LED light is
focussed and wire may put out a substantially higher light energy level than
is obvious.

Given all the above, I suspect that an efficient supply may need less power
than the flash does BUT not as little as one may have expected. Perhaps 100
mW - 500 mW range ?


       Russell McMahon


* arcane engineering optical flux unit

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2004\08\23@084033 by hael Rigby-Jones

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{Quote hidden}

Details on the impedance of the wire itself seems to be a little thin on the
ground.  However, generaly the wire requires 100-130volts at around 4000Hz.
Frequency affects brightness as well as colour in some types of EL material.

The cheap inverters you can buy typicaly take 12volts at 25mA powering a
couple of feet of EL wire (300mW good guess Russel!)  but are definitely not
noted for their efficiency.

I have seen AA powered inverters that suggest the wire can be illuminated
for 18 hours from two AA cells, but I suspect they are running the wire at
very low currents.

http://www.elwirecheap.com/faqs.html

Regards

Mike

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2004\08\23@091546 by Russell McMahon

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> The cheap inverters you can buy typicaly take 12volts at 25mA powering a
> couple of feet of EL wire (300mW good guess Russel!)

That wasn't guessing. That was BOTE engineering ;-)

> I have seen AA powered inverters that suggest the wire can be illuminated
> for 18 hours from two AA cells, but I suspect they are running the wire at
> very low currents.

AA Alkaline 2500 mAh typical
2500/18 ~~= 130 mA so capacity will be perhaps slightly lower than that ?
Say mean voltage delivered to inverter = 1.25V
1.25 x 2500/18 ~= 175 mW

which as you say may be somewhat dim.
Our super rough data points seem to be dropping into a consistent range.

       RM

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2004\08\23@152022 by William Chops Westfield

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On Aug 23, 2004, at 5:13 AM, Russell McMahon wrote:

> Given all the above, I suspect that an efficient supply may need less
> power than the flash does BUT not as little as one may have expected.
> Perhaps 100 mW - 500 mW range ?
>
Heh.  One advantage of "active" regulation by some CPU would be the
ability of the same processor to measure efficiency to some extent...
I'll think about that.  It might be interesting.

BillW

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