A simple circuit for direct current (dc) measurement using a transformer is proposed. The circuit is based on nonlinear effects in the transformer ferromagnetic core, and it provides information about the current magnitude and polarity. The circuit is analyzed applying piecewise-linear model of the core magnetization curve. An averaged-circuit model and the circuit transfer function are presented. Good linearity and wide measurement range are obtained. Design guides for reduction of the output voltage ripple are given. Measurement error within 0.25% of the full scale is achieved.
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