Abstract
Active gate driving has been demonstrated to beneficially shape switching waveforms in Si- and SiC-based power converters. For faster GaN power devices with sub-10-ns switching transients, however, reported variable gate driving has so far been limited to altering a single drive parameter once per switching event, either during or outside of the transient. This paper demonstrates a gate driver with a timing resolution and range of output resistance levels that surpass those of existing gate drivers or arbitrary waveform generators. It is shown to permit active gate driving with a bandwidth that is high enough to shape a GaN switching during the transient. The programmable gate driver has integrated high-speed memory, control logic, and multiple parallel output stages. During switching transients, the gate driver can activate a near-arbitrary sequence of pull-up or pull-down output resistances between 0.12 and 64 Ω. A hybrid of clocked and asynchronous control logic with 150-ps delay elements achieves an effective resistance update rate of 6.7 GHz during switching events. This active gate driver is evaluated in a 1-MHz bridge-leg converter using EPC2015 GaN FETs. The results show that aggressive manipulation of the gate-drive resistance at sub-nanosecond resolutions can profile gate waveforms of the GaN FET, thereby beneficially shaping the switch-node voltage waveform in the power circuit. Examples of open-loop active gate driving are demonstrated that maintain the low switching loss of constant-strength gate driving, while reducing overshoot, oscillation, and EMI-generating high-frequency spectral content.
Highlights
A CTIVE gate driving dynamically changes the gate resistance [1]–[6], gate voltage [7]–[9], or gate current [10]–Manuscript received October 26, 2016; accepted January 31, 2017
Experiment 1: Speeding Up Turn On. The aim of this experiment is to demonstrate that active gate driving can suppress gate voltage overshoot and, allow faster driving than is possible with constant-strength driving
The result is that active gate driving has allowed the speed of 2 Ω driving to be combined with the gate voltage overshoot of 3.6 Ω driving
Summary
A CTIVE gate driving dynamically changes the gate resistance [1]–[6], gate voltage [7]–[9], or gate current [10]–. In bridge-leg topologies, it implies an increase in the dead time that further increases power loss [19] Another reported challenge is that commercially available low-voltage GaN devices exhibit a low margin between the gate-source voltage required to enhance the channel, and the absolute maximum gate-source voltage above which the gate is permanently damaged [20]. This paper is organized as follows: Section II presents the 150-ps high-speed programmable resistance gate driver for GaN FETs. In Section III, this gate driver is modeled and simulated in a GaN-based switching circuit, and gate driving strategies for shaping the turn-on and turn-off switching waveforms are provided. This paper focusses on three example objectives: 1) turning GaN gates on faster, without incurring gate voltage overshoot; 2) eliminating overshoot in switch-node voltage waveforms; 3) attenuating high-frequency components of switch-node voltage spectra
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