Application of Tunnel Magnetoresistance for PCB Tracks Current Sensing in High-Frequency Power Converters.

In power converters, current sensing is essential for protection and control. Tunnel magnetoresistance (TMR) is considered a promising current sensor for its high sensitivity, low power consumption, small footprint, and noninvasively measurement. However, the fast voltage commutations and skin effect in high-frequency power converters will induce voltage spikes and gain variations in the TMR sensor output. A comb-shaped shield is presented to decrease output spikes generated by fast voltage commutations of power devices. The optimal comb-shaped shield parameters are designed to shield the electric field without affecting the magnetic field. This article also identifies the install location least affected by the skin effect and gives the formula for the optimal mounting position of the TMR for printed circuit board (PCB) tracks of different widths. The comb-shaped shield and the optimal position ensure TMR current measurement accuracy across a wide switching frequency range. A prototype was built to demonstrate the feasibility of the proposed methods. The TMR output spike is decreased from 0.17 to 0.02 V by adding the designed comb-shaped shield. The TMR in the optimal location can noninvasively measure the 0-1-MHz current and ensure the measurement amplitude fluctuation within 5%.