This invention includes a thermally stable, low-cost charging circuit for
rechargeable batteries. The circuit includes a thermal control circuit
that employs a temperature dependent component such as a thermistor or
positive temperature coefficient device. The temperature dependent device
is thermally coupled to a charging pass element, which is typically a
power transistor. When the transistor enters a danger zone, which is a
region of operation characterized by elevated power dissipation in the
pass element, the thermal control circuit is actuated to regulate the pass
element in a constant power mode until the circuit exits the danger zone.
