Novel GaN Power Transistor Substrate Connection to Minimize Common Mode Noise

Fast switching of GaN device would increase power converter common mode current I-cm level. In this paper, it is proposed to connect substrate of the upper device in a half-bridge circuit to its drain terminal in order to decrease capacitive coupling between device switching node and ground plane so as to decrease I-cm level. Device static and dynamic ON-state resistance and its inter-electrode capacitance are compared under different substrate connections, which shows that device static and dynamic characteristics do not noticeably degrade when connecting its substrate to drain terminal than conventional connection to its source terminal. Furthermore, I-cm magnitude is reduced over the whole 150kHz to 30MHz conducted EMI frequency range, with 2dB-3dB reduced level between 150kHz to 3MHz and more than 5dB reduced level around 20MHz when device switches at 100V and 200V with switching frequency of 100kHz.