There's been plenty of talk about the progress of gallium nitride over the past couple of years. Discussions generally revolved around its potential for greater operating efficiencies. Still, the question remains: “At what cost?”
In a recent article, Alex Lidow, CEO of the Efficient Power Conversion Corp. (EPC), says that as manufacturing experience and volume grows, the price for GaN transistors will decline. Semiconductor learning curves apply just as they did 33 years ago when the MOSFET was competing with the bipolar transistor. Lidow maintains that somewhere in the second half of this decade, driven by the second- and third-generation metal organic chemical-vapor-deposition reactors used to grow GaN heterostructures on silicon wafers, the cost of a GaN transistor will fall below a power MOSFET of equivalent power-handling capability.
I think that statement is correct, and when such a scenario emerges, the number of applications for GaN-based technology will rocket. Indeed, it’s already clear that GaN is making serious inroads into application areas that were, up until now, the securely held territory of the power MOSFET.
Lidow cites increased use of GaN in RF envelope tracking systems and wireless power-transmission systems, dc-dc converters for datacom applications, point-of-load converters, isolated brick converters, and power over Ethernet power-sourcing equipment. GaN transistors offer significantly higher power density and dramatically lower losses than their counterparts that use the power MOSFET, says Lidow.
GaN transistors are making an impact in other applications, too, such as class-D audio, solar micro-inverters, low-voltage brushless dc motor drives, and LED lighting.
EPC recently released safe-operating-area (SOA) data for its product line of eGaN FETs. The company says the positive temperature coefficient across virtually its entire operating range allows for a square SOA limited only by average device temperature.
SOA indicates how well a device can transfer heat away from a resistive junction. Greater efficiency in removing generated heat translates into reduced thermal resistance and better overall SOA performance. EPC says its eGaN FETs provide good device on-resistance, while its positive temperature coefficients inhibit hotspot generation within the die, resulting in higher SOA capabilities.
The company also recently announced a high-efficiency wireless power demonstration system. It exploits the high-frequency switching capability of GaN transistors.
Wireless Power Transfer
The founders of WiTricity invented highly resonant wireless power transfer. The company licenses its intellectual property to companies seeking to build products based on this new technology.
WiTricity’s technology is capable of transferring power over distance, enabling a range of consumer, medical, industrial, and automotive applications. Products using highly resonant wireless power transfer can meet stringent regulatory guidelines, and remains a safe option for people and animals.
Many wireless charging products employ traditional magnetic induction coils with operating frequencies between 100kHz and 300kHz, as well as Class E, F, and S amplifier converter topologies. Recently, organizations like the Consumer Electronics Association and A4WP (Alliance for Wireless Power) have called for a higher frequency standard (6.78MHz) for wireless charging systems. At higher frequencies, traditional silicon-based power transistors (MOSFETs) approach the limit of their switching capability.The wireless power demonstration system, jointly developed by EPC and WiTricity, is a class-D power system operating at 6.78MHz that can deliver up to 15W to a load. The purpose of the demonstration system is to simplify the evaluation process of wireless power technology. The system includes all of a single system’s critical components that can be easily connected to demonstrate how a device is powered with wireless energy transfer.