The standard way to change the converters output voltage would be to change
the switching frequency/pulsewidth.
Johannes
> -----Original Message-----
> From: newtontalk-bounce_at_newtontalk.net
> [mailto:newtontalk-bounce_at_newtontalk.net]On Behalf Of Marco Mailand
> Sent: Tuesday, July 02, 2002 11:31 AM
> To: newtontalk_at_newtontalk.net
> Subject: Re: [NTLK] Adjustable backlight?
>
>
>
> On 30.6.2002 7:10 Uhr, "Jim Witte" <jswitte_at_bloomington.in.us> wrote:
> > I asked PCBMan a while back and he said not to put a resistor in
> > series with the EL foil to drop the voltage because it could break the
> > inverter (he didn't say why, but I'm guessing it might have something to
> > do with the fact that the inverter puts out AC and the resistor doesn't
> > have a capacitive load component.)
> Since the inverter is basically a transformer it is not resistive and
> neither capacitive but inductive. Whatever it is its drive electronics are
> designed to handle the impedance an accept changes. An additional resistor
> in series with the BL foil which appears like capacitance does at
> least not
> overload the drive but waste energy as heat. The better approach
> would be t=
> o
> reduce the drive *input* voltage and thus have a large resulting change in
> the output voltage (That=B4s what I wanted to say in my 1st post).
>
> > Instead of trying to hook it into the inverter that's built in to the
> > Newt, would it be possible to fit another inverter into the case, hooked
> > in parallel to the battery/AC, and then wire a timer into the power
> > switch to detect the "hold" condition (and not use Apple's BL circuit at
> > all?)
> Of course and I do have a spare drive electronics board, thanks to Frank
> Gruendel. There is still the question of space. The transformer and the
> additional circuitry will take up some space but one could sacrifice e.g.
> The pen slot (that=B4s where the PCB I got is designed for.)
>
> Another idea would be to add a chain of capacitors in series with the BL
> foil and short them to get full brightness. The result will be brightness
> adjustment in at least two steps but very simple and cheap.
> --
> Marco
>
>
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