Bus interface for coupling a field device to a field bus

摘要

The connection has a circuit (5) for sending and receiving databus signals (RxD, TxD, RTS) and for generating a regulated operating voltage (Ua1). A controllable resistor e.g. bipolar transistor or FET, generates an additional operating voltage. A circuitry unit controls the controllable resistor as a function of a bus voltage (Ubus) such that an input voltage (Ue) of the circuit is regulated with a minimum required power supply voltage. The sum of the regulated operating voltage and the additional operating voltage is supplied to a field device (2) as a power supply voltage.