Qorvo has picked depletion-mode (normally-on) silicon carbide JFET technology to build a 750V 4.3mΩ transistor for circuit breakers, and put it in a 10 x 12mm surface-mount TOLL package.

Qorvo UJ4N075004L8S SiC jfet
“It was designed for circuit protection applications including solid-state circuit breakers, where low resistance, thermal performance and reliability are paramount,” according to the company. This “JFET can withstand high instantaneous junction temperatures without experiencing degradation or parametric drift. The normally-on nature of the JFET lends itself to integration into systems where the switch is in the on-state by default and in turn-off state under fault conditions”.

UJ4N075004L8S, as it will be known, is sampling now with production scheduled for Q4.

4.3mΩ is a achieved with +2V on the gate (80Ads Tj=25°C), rising to 9.9mΩ at Tj=175°C.

Qorvo SiC jfet bidir circuit breakerNormally-on bi-directional JFET switch

With 0V on the gate the typical figures are 4.9 and 11.5mΩ respectively. The only max figure is 6.6mΩ at Vg=0V Tj=25°C.

A gate drive of -20V is expected to turn the device off. To improve gate drive fidelity, there is a separate source terminal for the driver.

For improved thermal resistance, die attach is silver-sintered to typically achieve 0.10°C/W junction-to-case (0.13°C/W max).

Qorvo cascode SiC jfet bidir circuit breaker

Low-voltage enhancement-mode silicon mosfets need to be cascoded with the normally-on depletion-mode SiC JFETs to make a normally-off bi-directional power switch

The device is short-circuit rated for 5μs from a 400V Tj=175°C start.

The company also has 750V 5mΩ and 1.2kV 8mΩ jfets in TO-247 packaging.

Can an normally-on component be used in circuit breakers? 

“Based on our engagements with lead customers,” Qorvo tole Electronics Weekly, “we can confirm that our JFET technology is suitable for use in miniature circuit breakers as they migrate from electromechanical to semiconductor relays.  We offer guidelines on using our normally on JFETs as a replacement for a normally-closed relay or for a normally-open relay.”  Find the company’s JFET user guide here (click on ‘Proceed’ on the web page, not the part number) which includes descriptions of the diagrams above.