What is the current rating of a Qorvo SiC JFET in a circuit breaker or relay application?

Generally, there are two current capabilities of interest in circuit breaker and relay applications. First is steady-state current, which is limited by the cooling capacity of the circuit breaker/relay system. Typically, cooling capacity is extremely limited in a circuit breaker, so the allowable heat generation is very small. The usable steady-state current limit is much lower than the DC current limit in the datasheet. For example, a practical steady-state current for a single 750 V, 4.3 mOhm JFET UJ4N075004L8S in a (bottom-cooled) TOLL surface-mount package is typically 15 A, whereas it steady-state current limit in the datasheet exceeds 100 A.

The second current capability of interest is the peak current and its duration. The transient thermal impedance graph is useful here. If the current pulse is rectangular pulse, the effective thermal impedance is read from the graph based on the pulse duration. This thermal impedance multiplied by the estimated power dissipation yields the junction-to-case temperature rise at the end of the pulse. If the current pulse is not rectangular, then the Foster transient thermal impedance model is useful to simulate the temperature rise in QSPICE or other simulators.