Transistor arrangement

Claim 2

A circuit arrangement comprising: - a first transistor of a first conductivity type having an emitter coupled to a first power-supply terminal, a collector coupled to an output terminal, and a base, - a drive circuit for driving the first transistor, which drive circuit is coupled to a second power supply terminal and has an output coupled to the base of the first transistor, and - a limiting circuit for limiting the voltage between the emitter and the collector of the first tran­sistor to a specific value by reducing the drive to the first transistor when said voltage decreases below said value, characterized in that the limiting circuit comprises a first resistor arranged between the output of the drive circuit and the base of the first transistor, and a second transistor of the first conductivity type having an emitter coupled to the collector of the first transistor, a col­lector coupled to a control input of the drive circuit, and a base coupled to that end of the first resistor which is situated nearest the drive circuit.

Claim 3

A circuit arrangement as claimed in Claim 1, characterized in that the drive circuit comprises a third transistor of a second conductivity type, having an emitter coupled to a second power-supply terminal by means of a second resistor, a collector coupled to the output of the drive circuit, and a base coupled to a circuit for sup­plying a control voltage to the third transistor, and in that the control input of the drive circuit is constituted by the emitter of the third transistor.

Claim 4

A circuit arrangement as claimed in Claim 1, characterized in that the drive circuit comprises a third transistor of the first conductivity type, having an emit­ter coupled to the output of the drive circuit, a collector coupled to the second power-supply terminal, and a base coupled to a circuit for supplying a control current to the third transistor, and in that the control input of the drive circuit is constituted by the base of the third transistor.

Claim 5

A circuit arrangement as claimed in Claim 3, characterized in that the circuit for supplying a control current to the third transistor comprises a constant-current source for supplying a first current and a detection circuit for supplying a second current which is proportional to the difference in the voltage between the output terminal and the second power-supply terminal and a reference voltage, and in that the control current is formed by the difference between the first current and the second current.

Claim 6

A circuit arrangement as claimed in Claim 4, characterized in that the constant-current source comprises a fourth transistor of the first conductivity type, having an emitter connected to the first power-supply terminal, a collector connected to the second power-supply terminal by a second resistor, and a base coupled to its collector, and in that the circuit arrangement further comprises a fifth transistor of the first conductivity type, having an emitter coupled to the emitter of the fourth transistor, a collector connected to the collector of the fourth transistor, and a base, and a sixth transistor of the second conductivity type, having a collector connected to the base of the fifth transistor by a third resistor, an emitter connected to the second power-supply terminal by a fourth resistor, and a base connected to a switching input for applying a switching voltage, and a seventh transistor of the first condctivity type, having an emitter connected to the collector of the fifth transistor, a collector connected to the emitter of the sixth transistor, and a base connected to that end of the third resistor which is connected to the collector of the sixth transistor.