What is the application of silicon carbide Schottky diode in PFC circuits?

What is the effect of the steady-state and transient characteristics of the silicon carbide diode on the PFC, and what happens when the reverse recovery current occurs?

1. The influence of steady-state and transient characteristics of silicon carbide diodes on PFC

The basic topology of a continuous-mode boost converter. It is widely used in power factor correction circuits, and the inductor current is in continuous mode. In this circuit, the steady-state and transient characteristics of the diode have a strong influence on the PFC circuit.

2. Steady-state characteristics - the forward voltage Uf silicon material ultrafast recovery diode (15A/600V) is tested at room temperature. At 2~5A, the forward voltage drop is basically unchanged and close to saturation, which shows that the forward voltage drop of the silicon material diode becomes smaller at high temperature from another side, and the diode has negative temperature characteristics.

Silicon carbide Schottky diodes (4A/600V) are tested for forward voltage drop at room temperature. When the load current changes at 0~4A, the forward voltage drop basically increases linearly, which shows that the forward voltage drop of the SiC Schottky diode increases linearly at high temperature, indicating that the SiC diode has positive temperature characteristics.

In high-power PFC circuits, diodes may need to be used in parallel to expand the capacity, and the current distribution of the device needs to be considered, and the characteristics of the diode's forward voltage and on-resistance are key. The unique positive temperature coefficient of silicon carbide Schottky diodes ensures the current sharing requirements when the devices are connected in parallel.

Third, the transient characteristic - reverse recovery current

There are many types of diodes, but only the task of carrying the current of the Schottky barrier diode is completed by the majority of carriers, there is no excess minority carrier recombination, the recovery time is very small, about tens or hundreds of ps, the disadvantage is that its withstand voltage is very low. Other silicon diodes (such as ordinary diodes, fast diodes, ultrafast recovery diodes) and other current-carrying tasks are performed by a small number of carriers, and there is a problem of reverse recovery time. The two ultrafast recovery diodes used have a Trr time of 30ns and 13ns respectively, but this reverse current problem is not avoided.

Due to the characteristics of the material, the silicon carbide Schottky diode has the advantages of both at the same time, not only the withstand voltage is very high, but also the reverse recovery characteristics and temperature characteristics are very good. The reverse current and reverse recovery time of the silicon rectifier will increase with the increase of temperature. The reverse recovery time and reverse current of SiC Schottky diodes are very small, and they have very good temperature characteristics, and their reverse recovery time does not change with increasing temperature. At room temperature 25°C, the reverse recovery time of the ultrafast recovery diode is 3 times that of the SiC Schottky diode, and the reverse current is 4 times that of the SiC Schottky diode. At a high temperature of 150°C, the reverse recovery time of the ultrafast recovery diode is 6 times that of the SiC Schottky diode, and the reverse current is 12 times that of the SiC Schottky diode.

In general, we all want the reverse recovery time of diode D1 in a single-phase PFC circuit to be as short as possible. Because the reverse recovery current can cause us a lot of problems, such as diode reverse recovery losses, and the resulting severe MOS