Measurement device with common mode current cancellation

摘要

The secondary of a line powered transformer supplies power to a measurement unit. The measurement unit measures between a high test terminal and a low terminal on the secondary. The low terminal is connected to a low test terminal through a common mode current sensor to a device under test. The device under test is also connected to the high test terminal. The common mode current sensor senses current through the transformer capacitance that flows through the device under test to earth ground. A current source is connected in parallel with the low terminal and earth ground. In response to the current sensor, the source dynamically drives a current through the device under test that drives the common mode current to a minimum.