Kelvin source connection benefits MOSFET efficiency in hard switching topologies

May 07, 2013 // By Graham Prophet
Infineon and ST have introduced a custom TO 247-4 pin package for its CoolMOS MOSFETs; the added fourth pin acts as a Kelvin source to effectively reduce the parasitic inductance of the source lead of the power MOSFET.


The efficiency benefit will be highest in various hard switching topologies such as Continuous Conduction Mode Power Factor Correction (CCM PFC), Boost and Two Transistor Forward (TTF).

The new package offers improved efficiency by reducing switching losses by up to 8%. This equates to 5W lower power dissipation on the MOSFET in a CCM PFC running at 1.2KW, which means 0.4% extra full load efficiency compared to the same MOSFET in the standard 3-pin TO 247 package. The new TO 247-4 is available from two companies: both Infineon and STMicroelectronics are introducing this package providing customers with a high-quality alternative source.

“The latest generation of Superjunction MOSFETs is able to switch several hundreds of volts and several tens of amperes within a few nanoseconds. To reach the full benefit of the chip technology the package is an important factor to set up an appropriate system environment which is crucial to reach the next level of energy efficiency,” said Jan-Willem Reynaerts, Product Segment Head of High Voltage Power Conversion at Infineon Technologies. “This new TO 247-4 pin package for High Voltage MOSFETs, today being introduced by Infineon as well as STMicroelectronics, is setting new energy efficiency standards.”

An additional benefit of the Kelvin source configuration in the TO 247-4 is the ease of use for the PCB layout due to its new pin arrangement with the exposed drain and the source between gate and drain. This reduces the critical drain to gate coupling, which often causes gate oscillations at turn off with high dv/dt rates of the Drain-Source Voltage (V DS). Furthermore, the increase of creepage distance between drain and source improves system reliability. The new package is optimised for high power applications such as server, telecom and solar energy.

CoolMOS C7 – the latest generation of Infineon’s Superjunction power transistors, which has been announced recently –will be the first Infineon MOSFET family using the TO 247-4 pin package.