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Novel design for a coreless printed circuit board transformer realizing high bandwidth and coupling
(2019)
Rogowski coils offer galvanic isolation and can measure alternating currents with a high bandwidth. Coreless printed circuit board (PCB) transformers have been used as an alternative to limit the additional stray inductance if a Rogowski coil can not be attached to the circuit. A new PCB transformer layout is proposed to reduce cost, decrease additional stray inductance, increase the bandwidth of current measurements and simplify the integration into existing designs.
Improved inductive feed-forward for fast turn-on of power semiconductors during hard switching
(2019)
A transformer is used to increase the gate voltage during turn-on, thus reducing the necessary bias voltage of the gate driver. Counteracting the voltage dependency of the gate capacitance of high-voltage power devices, faster transitions are possible. The additional transformer only slighly increases the over-voltage during turn-off.
A novel gate driving approach to balance the transient current of parallel-connected GaN-HEMTs
(2018)
To enable higher current handling capability of GaN-based DC/DC converters, devices have to be used in parallel. However, their switching times differ, especially if their threshold voltages are not identical, which causes unbalanced device current. This paper focuses on the homogeneous distribution of turn-on switching losses of GaN-HEMTs connected in parallel. By applying a new gate driver concept, the transient current is distributed evenly. The effectiveness of this concept is demonstrated by double pulse measurements, for switching currents up to 45A and a voltage of 400V. A uniform current distribution is achieved, including a reduction of the turn-on losses by 50% compared to a conventional setup.
Many GaN power transistors contain a PN junction between gate and the channel region close to the source. In order to maintain the on-state, current must continuously be supplied to the junction. Therefore, the commonly recommended approach uses a gate bias voltage of 12V to compensate the Miller current through a boost circuit. For the same purpose, a novel gate driving method based on an inductive feed forward has been presented. With this, stable turn-on can be achieved even for a bias voltage of only 5V. The effectiveness of this concept is demonstrated by double pulse measurements, switching currents up to 27A and a voltage of 400V. For both approaches a compact design with low source inductance is characterized. In addition to the significant reduction of the gate bias voltage and peak gate current, the new approach reduces the switching losses for load currents >23 A.