To detect a power supply failure on an intrinsically safe field bus of a manufacturing process control system in an efficient manner there is provided a field device with a discharge protection unit which is connected to a control bus for supply of an operating current from the control bus to the field device. The discharge protection unit inhibits a discharge of energy stored in the field device to the control bus. The field device also comprises a controller unit adapted to control the operation of the field device and being powered with the operating current from the control bus. According to the present invention the discharge protection unit comprises at least two rectifying elements inserted into the current path of the operating current with identical conducting directions and an input signal or an output signal of a selected rectifying element is supplied as interrupt signal to the controller unit for power supply failure detection.