A current sensor is provided that employs a primary winding that carries the current to be measured, and a secondary winding that controls the flux inside the magnetic core, provides a sample of the primary current, and also helps to control the flux at small primary currents and to saturate the transformer....http://www.google.com.hk/patents/US7834613?utm_source=gb-gplus-share專利 US7834613 - Isolated current to voltage, voltage to voltage converter
