Electric motors are becoming more widespread in vehicles as electric power steering and stop-start systems add to the volumes used by hybrid and electric vehicles. This growth is driving demand for power handling devices that are smaller yet still provide high current capabilities.
Infineon Technologies AG has developed a 40-V power MOSFET (metal-oxide-semiconductor field-effect transistor) that can handle up to 300 A while consuming little board space. The power devices are packaged in what’s called a Heatsink Plastic Small Outline Flat (H-PSOF) lead package, which is about 20% smaller and half the height of currently available alternatives.
“That’s an unprecedented amount of current in a part that’s only about a centimeter square,” said Jeff Darrow, Product Marketing Manager for Automotive MOSFETs for Infineon Technologies North America. “That’s enough current for an entire house.”
The parts are typically mounted on a circuit board without any heat sinks. Heat generation is reduced by turning the part off often.
“System designers will typically turn the part on and off 25 to 30 times a second,” Darrow said. “That’s a huge benefit over relays, which are now used for this amount of current. Relays can’t even turn off once a second.”
The power MOSFETs are applicable in electrified powertrains, but they are also expected to find use in technologies that are expected to see rapid growth as automakers strive to meet stringent new fuel regulations. Electric power steering (EPS) and engine stop-start are currently in use, but both are expected to move swiftly into the mainstream. Strategy Analytics predicts that they’ll have a compound average annual growth rate of about 19% through 2016.
“EPS has been used in smaller cars that don’t need big motors to turn the wheels,” Darrow said. “With rising fuel economy requirements, larger cars and SUVs will need EPS. These large motors need more current.”
Fuel-saving stop-start technology, which is seeing rapid adoption in Europe and requires very high power levels for the electric motors that start the movement of a car that’s standing still, may also benefit from the new-generation MOSFETs.
Current requirements for these motors are often around 600 A, going to 1 kA in cold temperatures. “You can achieve those levels with a couple chips or use three or four in parallel for higher current levels,” Darrow said.
However, he also noted that stop-start will require a change in battery technology. Conventional lead-acid batteries won’t support the many discharge functions associated with shutting the engine off instead of idling.