A protection circuit for use with a charger and a chargeable element, such as
a
rechargeable lithium ion battery, comprises a shunt regulator having a threshold
ON voltage coupled in parallel across the chargeable element, and a temperature-dependent
resistor, e.g., a positive temperature coefficient device, coupled in series between
the charger and the chargeable element. The temperature dependent resistor is thermally
and electrically coupled to the shunt regulator, wherein the first variable resistor
limits current flowing through the shunt regulator if the current reaches a predetermined
level less than that which would cause failure of the regulator, due to ohmic heating
of the regulator.
