System for measuring load current in an electronically controlled switch

摘要

A new sensor means for accurately measuring the current flowing in an electronically controlled switch is presented. An ac coupled current sensor is arranged in circuit with the electronically controlled power switch. The output of the sensor channel is zeroed (or restored to another fixed independent level) whenever the power switch is in the OFF condition. Using the natural modulation of the power switch itself to coordinate the reconciling of the sensor output level with the OFF state of the power switch helps restore to the dc level lost through ac coupling. This coordination of the sensor with the switch itself reduces dc offset and drift and allows ac coupling, which removes dc common mode and increases primary current sensor flexibility, all without adding complexity. A plurality of such sensors can be combined to measure indirectly the load current from a plurality of switches according to Kirchoff's Current Law.