We developed a thin-film current sensor using a flux-saturable ring core. The sensor consists of a transformer unit composed of a saturable core, primary and secondary coils, and a load coil surrounding the transformer unit. The sensor is suitable for use in a fail-safe system. The chip size is 4mm × 4mm. A transmission efficiency of 60% was obtained when the carrier signal was a 3 Vpp-1 MHz sine wave. The secondary voltage of the sensor dropped by 90% when a 100-mA load current was applied to a 20-turn load coil.
