PROTECTION CIRCUIT FOR RECHARGEABLE BATTERY CELLS

摘要

Protection circuit for rechargeable battery cells of the type sensitive if being charged by a charging source with a voltage exceeding a predetermined threshold level, that comprises a battery cel to be protected and a shunt path connected to the terminals of the battery cell, the shunt path is substantially non-conductive if the charging voltage is below the threshold level and it is conductive if the voltage approaches or exceeds said level so that current will flow dominantly through the shunt path instead of through the battery cell, wherein the improvement lies in that the shunt path comprises: a semiconductor switch means with an input junction and with a pair of output terminals, the input junction is connectable to the source of charging voltage for getting forward biased thereby, the output terminals of the switch are connected in the shunt path, the switch means is conductive on condition if the input junction is forward biased and if the voltage across the output terminals is not less than a predetermined threshold voltage lower than said threshold level, the switching means has a flat non-linear voltage-to-current characteristic; and diode means with a pair of terminals in series connection with the switching means, the diode means has a forward bias voltage measurable across said terminals if current flows therethrough; and the forward bias voltage of the diode means and the threshold voltage of the switching means have opposing temperature coefficients and define together said threshold level.