Lossless current sensing and its application in current mode control

In this paper, it is revealed that the lossless current sensing structure is very similar to the well known Maxwell bridge. The matching condition in lossless current sensing is the same as the balance equation in Maxwell bridge. In practice, it is difficult to meet the matching condition due to the parameter value variations. However, it is shown that in current mode control, at certain time constant mismatching situations, the circuit dynamic response actually could be improved. Furthermore, a “speedy capacitor” could be added to the lossless current sensing circuitry to significantly improve the sensed current signal to noise ratio and avoid jittery operation in wide DC-DC conversion ratio applications.