Patent ID: 6021037
Filing Date: 2000-02-01
Classification: H03K

Abstract:
A device (1) including a circuit arrangement (2) for supplying electric power to a load (4) connected to the device (1) in a power-on mode, comprising a driver stage (7), and a control unit (9) adapted to supply turn-on pulses to the driver stage (7), and an output stage (12) including a switching transistor (11), which switching transistor (11) can be turned on by the driver stage (7) in the power-on mode when turn-on pulses occur, to assume a conductive switching state for a time interval (T.sub.EIN), and can be turned off after expiry of the time interval (T.sub.EIN), to assume a non-conductive switching state, the driver stage (7) being adapted, in addition, to monitor the operating temperature (T.sub.S) of the switching transistor (11) and to activate a power-off mode, which mode is activated when the operating temperature (T.sub.S) of the switching transistor (11) exceeds a first limit temperature (T.sub.G1), in which power-off mode the switching transistor (11) is permanently driven into its non-conductive switching state by the driver stage (7) in spite of the occurrence of turn-on pulses, characterized in that the driver state (7) comprises a series arrangement of a base-emitter diode of a sensing transistor (21) and a sensing resistor (22), said series arrangement is connected in parallel with the base-emitter diode of the switching transistor (11), the base terminal of the sensing transistor (21) being connected to the emitter terminal of the switching transistor (11), and the driver stage (7) further comprises a turn-on transistor (23) having its base terminal connected to the collector terminal of the sensing transistor (21) and having its collector terminal connected to the base terminal of the sensing transistor (21), and the driver stage (7) further comprises a turn-on resistor (24) having a first terminal (25) connected to the emitter terminal of the turn-on transistor (23) and having a second terminal (26) connected to the collector terminal of the turn-on transistor (23), and the sensing transistor (21) has been arranged so as a to be substantially uninfluenced by the operating temperature (T.sub.S) of the switching transistor (11).