High Frequency PCB Trace Current Measurement in Power Converters Based on Tunnel Magnetoresistance

In power converters, current sensing is essential for control and protection. This paper employs tunnel magnetoresistance (TMR) to non-invasively measure the PCB trace current in high frequency power converters. The operating principle of the TMR sensor is briefly introduced. Then we discuss the influence of skin effect on TMR measurement delay and bandwidth. Based on the finite element method (FEM) simulations, optimal install locations of the TMR sensor are found to avoid the influence of skin effect. An empirical formula is provided to summarize the optimal install locations under different trace widths. By putting the TMR sensor at the optimal location, the measurement delay is reduced from 517ns to 102ns according to experimental results. Next, a comb-shaped shield is proposed to suppress the switching spikes of TMR sensor output caused by common mode noise. The parameters of the comb-shield are chosen such that the electric field are shielded without affecting the magnetic field distribution. With the proposed comb-shaped shield, the TMR output spikes is reduced from 0.20V to 0.05V, whereas the measurement delay is almost not affected (W/O-102ns, with114ns).