Abstract
Here, an ultra-fast protection scheme that is dedicated to depletion-mode (d-mode) devices is proposed. The key to the d-mode device gate drive design is the negative supply and overcurrent protection, due to the safety concern for d-mode devices when a failure happens in power conversion applications. This work evaluates specific requirement of d-mode devices, such as the isolated negative power supply and short-circuit protection. Normally-on d-mode GaN devices have lower on-resistance and minimal dead time in comparison with enhancement-mode (e-mode) GaN devices, which can further reduce the switching loss and conduction loss. Both simulation and experimental verification are conducted in this work to evaluate the performance of the proposed protection scheme. The proposed desaturation scheme can wipe out the overcurrent event within 341 ns. Furthermore, the proposed negative power supply scheme can sustain its output for 60.5 ms, providing sufficient action time for the control unit to isolate the converter.
Highlights
Wide bandgap (WBG) technologies such as Gallium Nitride (GaN) or Silicon Carbide (SiC) as emerging candidates to achieve the higher switching frequency and higher efficiency than Silicon (Si) counterparts in power converters
The polarisation super-junction (PSJ) GaN FET based converter is operating at 600 V/5 A, and Id _limit is set at 13 A; the SiC JFET-based converter is operating at 400 V/25 A, and 60 A has been set as Id _limit, corresponding with 2 and 1.4 V drain-to-source voltage respectively according to their IVcurve as depicted in Figure 7 at room temperature
According to the Equation (1), the Vre f as “IN-” of the comparator is set to 4.167 V of PSJ GaN FET and 3.846 V of SiC JFET
Summary
Wide bandgap (WBG) technologies such as Gallium Nitride (GaN) or Silicon Carbide (SiC) as emerging candidates to achieve the higher switching frequency and higher efficiency than Silicon (Si) counterparts in power converters. The inherent bidirectional current flow capability of GaN devices guarantees the interests of GaN for those applications, which require bidirectional switching operation, such as motor drives, EV chargers and server power supplies [4]. The 2DEG does not have to be disrupted and re-created to turn on the device [15] It is worth developing and exploring d-mode GaN devices to fully enable all advantages that GaN brings. This work proposes a gate driver design for normally-on GaN devices with effective protection in terms of the failure of negative gate voltage supply and the overcurrent/short-circuit event. GaN devices can exhibit the bidirectional current flow capability In this work, both the desaturation and negative power supply protection circuits are applied to a 1.2 kV polarisation super-junction (PSJ) GaN FET [20, 21].
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