Current-Sensing Topology with Multi Resistors in Parallel and Its Protection Circuit

Abstract

Current-sensing topology with multi resistors in series has limitations in improving the dynamic range of current acquisition, so a sensing topology with multi resistors in parallel is proposed. The overcurrent state of a parallel shunt circuit cannot be latched, resulting in protection hiccups. A dual threshold-detection circuit is designed to achieve protection state latching and self-recovery. The rectified mean circuit is applied for overcurrent magnitude detection and its validity is proved. But the delay and ripple of the output waveform of the rectified mean circuit may also cause protection hiccups. Combining Fourier series representation, Fourier transform and inverse transform, the time domain expressions of the output of the rectified mean circuit for three common waveforms are obtained. Furthermore, the estimation formulas for the residual ripple amplitude of the three waveforms are derived. In an experiment, the protection hiccup issue in parallel sensing topology was eliminated, while the time constants and hysteresis ratios of the protection circuits were properly set according to theoretical calculation results. With five parallel sensing resistors, the ratio of the maximum to minimum range of the single current channel reaches 1.28×104, which is higher than counterparts with multiple series sensing resistors. The advantages of parallel sensing topology in improving dynamic range are confirmed.

Keywords

• parallel resistors
• current sensing
• dynamic range
• protection hiccup
• rectified mean value