Lossless bi-directional current sense circuit for low-voltage high-current DC/DC converters

This paper proposes a new lossless bi-directional current sense circuit for low-voltage high-current bi-directional converters. Lossless current sensing is achieved by compensating the inductance of the inductor with a low pass filter. A new structure which adopts floating power rail, dc-biased current mirror and closed loop operation level-shifts and amplifies the output of the low pass filter. The difference between the output voltage and the reference voltage is proportional to the inductor current. The proposed circuit realizes high bandwidth bi-directional estimation of instantaneous inductor current without using costly high performance operational amplifiers. The elimination of the external current-sense resistor greatly improves the efficiency of the converter and the proposed circuit can be integrated into a variety of efficiency-critical high-current converters. The novel circuit is constructed and tested with a bi-directional converter. Experimental results demonstrate good agreement with theory and verify the excellent linearity and high bandwidth capacities of the circuit.