This Weekend's Finds

From: Tony Duell <ard_at_odin.phy.bris.ac.uk>
Date: Mon Aug 18 04:40:06 1997

> > Not so. A lot of machines use the NiCd as the smoothing component. HP
> > certainly did in just about all of their more recent NiCd calculators (the
> > ones that use the 8V 50mA AC charger).
>
> Interesting. I haven't found where the battery gets in, but the input
> stage is something like:
>
> Diode
> Ring --+--/\/\/-|>|-+-----+
> | 56R | \
> | |C / 82R
> | |/ \
> +-/\/\/-+--| NPN /
> | |\ |
> _ |E |
> Tip--+ Zener A +-----+--- +5V? to rest of machine (??)
> | |
> GND GND
>
> I would guess the battery could well do any smoothing downstream of the
> regulator, but I'd still like to see some upstream of it!

That looks like a voltage regualtor, which is strange, since I'd have
expected a constant current charger for the NiCd. Of course a lot of
machines just use a resistor to limit the charging current (and to get you
to buy more expensive battery packs)

>
> If the machine draws 60mA, minimum voltage at input is around 9V,
> maximum around 13V, so I suppose I could try 10V and see what happens...

Remember that you'll be charging this thing (probably) with the machine
turned off, so it's not going to be taking much current).

>
> > Some, like the Epson HX20 even used the fact that the voltage across the
> > NiCd would go above 5V to limit the supply voltage to the chips. The
> ^^^^^
> I take it you mean wouldn't

Of course I did. Sorry for the typo.

> Philip.

-tony
Received on Mon Aug 18 1997 - 04:40:06 BST