Positive Characteristics of SiC-SBD
The turn-on voltage of the silicon carbide Schottky barrier diode (SiC-SBD) is the same as that of the silicon-based fast recovery diode (Si FRD) and is less than 1V. The turn-on voltage is determined by the barrier height of the Schottky barrier. Generally, if the barrier height is designed to be low, the turn-on voltage can be made lower, but this will also increase the leakage current during reverse bias. Therefore, for different application environments, it is necessary to compromise the SiC-SBD on-state current and reverse leakage. As shown in Fig. 1, the temperature dependence of SiC-SBD is different from that of Si FRD. The higher the temperature, the higher its on-resistance increases, and the Vf value also increases. It is not prone to thermal runaway, so it can be safely used in parallel.
Fig.1 Dependence of forward conduction characteristics of SiC-SBD on temperature
Recovery Characteristics of SiC-SBD
As shown in Figure 2, the Si-FRD will generate a very large transient current at the instant of switching from forward to reverse. During this time, it will shift to the reverse-bias state, resulting in large losses. This is because the minority carriers that accumulate in the drift layer when positively energized continue to conduct electricity until they die (this time is also referred to as accumulation time). The larger the forward current or the higher the temperature, the larger the recovery time and recovery current, and the greater the loss. In contrast, SiC-SBD is a majority-carrier device (unipolar device) that does not use minority carriers for electrical conduction, so the phenomenon of minority carrier accumulation does not occur in principle. Since only a small current that causes the junction capacitance to be discharged is generated, the loss can be significantly reduced as compared with the Si-FRD. Moreover, this transient current does not substantially change with temperature and forward current, so that rapid recovery can be stably achieved regardless of the environment. In addition, the noise caused by the recovery current can also be reduced to achieve the effect of noise reduction.
Figure 2 Reverse Recovery Characteristics of Si-FRD and SiC-SBD
Dependent on forward current and temperature
At present, SiC SBDs with voltage levels of 600V, 1200V, 1700V, and 3300V have been commercialized, and SiC SBDs with voltages of more than 3300V have been studied globally. Since SiC-SBD has obvious advantages in both forward conduction and reverse recovery characteristics relative to Si-FRD. Therefore, if SiC-SBD is used instead of the current mainstream product fast recovery diode (FRD), recovery loss can be significantly reduced. This helps to increase the efficiency of the power supply, and realizes miniaturization of passive components such as inductors through high-frequency driving, and noise reduction. The devices are widely used in power factor correction circuits (PFC circuits) and rectifier bridge circuits such as air conditioners, power supplies, power conditioners in photovoltaic power generation systems, and quick chargers for electric vehicles.
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