Abstract
The progress of microelectronics and microprocessors has advanced digitization of control circuits so that sensors have been expected to have digital output. Current sensors are basic in electrical drives, and the control accuracy depends on their performance. However, a current sensor using Hall-device has a non-linear error of 1%. In order to solve this problem, a Hall-effect current sensor, or a so-called closed loop current sensor, has been developed, which is combined with a current transformer. The current of a secondary winding is compensated by the Hall-device so that the magnetic field in the toroidal core is kept at zero. In this case, the non-linear error is eliminated.
In this paper, a digital output current sensor of 12 bits is developed, which is a combination of a closed loop current sensor with a voltage comparator and a counter. As this circuit includes a nonlinear component such as the voltage comparator, the limit cycle caused by non-linearity is analyzed. It is described that the oscillation can be suppressed by linearization using a flush type A/D converter of 4 bits.
