Patent ID: 8018201

Claim:
An apparatus for charging a battery, comprising: a first transistor with a base, through which a charging current flows to a battery connected to the first transistor when said battery is being charged; a current source for a control current for said transistor, said current source being connected to the base of the first transistor to supply said control current wherein said current source includes an adjusting arrangement for adjusting or setting said control current, so that the first transistor is non-conducting or blocked and said charging current flowing into said battery is shut off when a predetermined maximum charging voltage at said battery is reached; a Zener diode arrangement, wherein said Zener diode arrangement is connected with said base of said first transistor, said Zener diode arrangement having a Zener voltage, wherein the Zener diode arrangement, in cooperation with the adjusting arrangement of the current source, causes the first transistor to become nonconducting when the battery reaches a predetermined maximum supply voltage so that the charging current is interrupted; a second transistor, wherein an emitter of the second transistor is connected with the base of said first transistor, a base of said second transistor is connected with the collector of said first transistor via an resistor-capacitor circuit path, having a resistor and a capacitor, and the collector of said second transistor is connected to said current source, wherein said second transistor keeps said control input of said first transistor at a potential that is less than the charging voltage of said battery connected to said first transistor after blocking said first transistor such that the base-emitter path of the first transistor is reliably blocked, and wherein the current source includes a third transistor and a fourth transistor, a first resistor and a second resistor, wherein the base of the third transistor is connected with the collector of the fourth transistor and the base of the fourth transistor is connected with the emitter of the third transistor and the emitter of the third transistor and the base of the fourth transistor are connected via a second resistor with the base of the first transistor and the emitter of the fourth transistor is connected with the base of the first transistor.