A Gate Driver with a Negative Turn Off Bias Voltage for GaN HEMTs

The GaN HEMT offers fast switching and low on-state resistance which makes it ideal for applications such as high efficiency and high power density power supplies. Unfortunately, the low threshold voltage makes GaN HEMT extremely vulnerable to false turn-on, which compromises the performance and potentially causes shoot-through. In the half-bridge circuit topology, the resonant circuit formed by the parasitic inductance and capacitance can trigger false turn-on with a fast commutation. A practical method to avoid this phenomenon is to apply a negative bias voltage during the commutation by either using a separate power supply or using a capacitor charge pump to produce the negative turn-off bias. The first method necessitates many extra components and the second method cannot provide a fixed negative voltage. This paper rectifies these issues by proposing a negative turn-off bias generator with a new charge pump based approach which offers a stable negative turn-off voltage under different switching frequencies and duty cycles. The proposed circuit has been practically implemented during experimental testing. These results demonstrate that false turn-on events are eliminated without compromising the high-frequency and highspeed characteristics of the GaN HEMT.