Why does the 200lx need a 12V supply?

[Harald]

I was wondering why the 200lx needs a 12V supply. It seems a little odd as it runs of 2AA cells.
When you drop the input voltage the current doesn't change (it draws about 45mA), it simply switches over to battery power at about 9V. So it doesn't look like the 12V are going to a dc/dc converter.
Also, in off state it draws 13mA which seems a little high.

From the battery it draws 60 to 70mA when running and almost nothing when turned off.

Does anybody have schematics of the 200lx, especially the (internal) power supply circuit?

Regards,
Harald

[Dave Frederickson]

Perhaps because the NiCd charging circuit requires more voltage.

Dave

[Gerson W. Barbosa]

(07-25-2014 12:29 PM)Harald Wrote:  Does anybody have schematics of the 200lx, especially the (internal) power supply circuit?

No schematics, just a picture of a spare motherboard with some voltage indications, in case this might be useful:

https://www.dropbox.com/s/o2g69s2ycp0jgv...0LX_MB.JPG

Regards,

Gerson.

[Katie Wasserman]

(07-25-2014 12:29 PM)Harald Wrote:  I was wondering why the 200lx needs a 12V supply. It seems a little odd as it runs of 2AA cells.
When you drop the input voltage the current doesn't change (it draws about 45mA), it simply switches over to battery power at about 9V. So it doesn't look like the 12V are going to a dc/dc converter.
Also, in off state it draws 13mA which seems a little high.

From the battery it draws 60 to 70mA when running and almost nothing when turned off.

Does anybody have schematics of the 200lx, especially the (internal) power supply circuit?

Regards,
Harald

Don't be fooled by the 2 AA batteries. This is a complex machine that generates it's own internal voltage rails from those 2 cells.

I think the reason for an external 12 Volt supply is.....

PCMCIA cards require a 12 volt rail at a low current (around 100ma) for writing and higher current (500ma) requirements at 3.3 volts or 5 volts for control/reading. Add to that the current consumption of the 200LX itself and more to charge the (optional) nicad cells. This can easily add up to several watts and using a 12 V (10 volt minimum) external supply allows for a lower current draw (thinner cable) from the wall wart.

I don't know of a schematic for the 200XL but here's some more about the internal power supply.

[Harald]

Thanks everyone!