Abstract: A current output apparatus adapted for electrical connection to a load to output an electrical current thereto. The apparatus comprises a current output terminal for connecting to a first terminal of the load to pass an electrical current thereto. A current input terminal is provided for connecting to a second terminal of the load to receive said electrical current returned from the load. A voltage regulator is operable to supply to the current output terminal an electrical voltage regulated to differ from an electrical voltage applied to the current input terminal by an amount sufficient to cause said electrical current to flow from the current output terminal to the current input terminal via the load.

Abstract: A current output apparatus adapted for electrical connection to a load to output an electrical current thereto. The apparatus comprises a current output terminal for connecting to a first terminal of the load to pass an electrical current thereto. A current input terminal is provided for connecting to a second terminal of the load to receive said electrical current returned from the load. A voltage regulator is operable to supply to the current output terminal an electrical voltage regulated to differ from an electrical voltage applied to the current input terminal by an amount sufficient to cause said electrical current to flow from the current output terminal to the current input terminal via the load.

Abstract: An electrical barrier for connecting a power supply to electrical equipment to be used in a potentially explosive area. The barrier includes a shunt zener diode for limiting the output voltage and a series resistance for limiting the current. In the arrangement shown, the shunt zener diode is a silicon carbide zener diode which has a higher resistance to large output current and/or operating temperature than zener diodes fabricated commercially.

Abstract: An electrical barrier (10) for connecting a power supply to electrical equipment situated in a potentially explosive atmosphere comprises an input (12), output (13), a shunt zener diode (14), a fuse (15), an output resistor (16) and the sensor resistor (11). The zener diode (14) is operable to limit the output voltage of the barrier. In some embodiments multiple zener diodes are used if desired or appropriate. The output resistor (16) acts to limit the maximum output current whilst the fuse (15) acts to prevent operation of the barrier in the event of an excessive input. The sensing resistor (11), being in series with the zener diodes (14), allows the current flowing through the zener diode (14) to be determined. The value of this current is then used to regulate the voltage input to the barrier (10). By using such a sensing resistor in series with the zener diode (14), the voltage on the zener diode (14) can be controlled so that the desired current flows.