6 Jun
2019
6 Jun
'19
9:34 p.m.
On Thu, Jun 6, 2019 at 9:57 PM Tony Duell via cctalk <cctalk at classiccmp.org>
wrote:
HP were fond of using NiCds as shunt regulators at
that time. The did
it in many of
their handheld calculators (HP20 series 'Woodstock', HP30 series
'Spice', etc). In
those it wasn't normally a problem (the calculator electronics drew
enough current to
pull the voltage down) except in machines with 'continuous memory'
(battery backed
RAM). There, if the machine it turned _off_ the RAM is the only thing
drawing current
and it doesn't draw enough to pull the voltage down below the zapping
level.
The should have paralleled the battery with zener with a voltage somewhat
above the normal battery charging voltage but below the abs max rating of
the power supply pins of the chips. They saved maybe ten cents by omitting
that.