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Gallium nitride (GaN) is becoming a technology of choice for several power conversion applications, including DC-DC converters for renewable energy applications in wind and solar systems. The move to GaN enables higher frequencies, improving response time for changing load currents compared to silicon-based DC-DC converters.
While GaN-based DC-DC boost converters are widely used in data centers, computing and automotive applications, they’re also increasingly employed in smart grid implementations like solar inverters and motor drives for wind turbines. Here, both discrete and integrated GaN solutions demonstrate energy efficiency and power density that’s at least twice as much as possible with silicon MOSFETs.
The potential of GaN to boost conversion efficiencies and increase power densities is universally acknowledged, according to Nigel Salter, general manager at RAM Innovations. His company has partnered with Cambridge GaN Devices to package GaN-based DC-DC converters for industrial, automotive and aerospace applications.
Alex Lidow, co-founder and CEO of Efficient Power Conversion (EPC), acknowledges this shift in power conversion designs. “GaN FETs can achieve the maxim power density for DC-DC converters.”
EPC has recently joined hands with Analog Devices and Renesas to help create high-density, low-cost DC-DC converters.
Two design examples
EPC has combined its eGaN FETs with a controller IC from Renesas to create a demo board that converts a 12-V input to a 48-V regulated output with a 500 kHz switching frequency. The output voltage can be configured to 36 V, 48 V and 60 V, and the board can deliver 480 W power without a heatsink.
EPC9166, a 500-W DC-DC demo board, combines EPC2218 eGaN FETs from EPC with Renesas ISL81807—an 80-V two-phase synchronous boost controller, which doesn’t require a microcontroller (MCU), current sense op amp, external driver or bias power. It also features light load operating mode, adjustable dead time and over-current protection.
In a similar design undertaking, EPC teamed up with Analog Devices to develop a reference design board that operates at 500-kHz switching frequency and converts an input voltage of 48-54 V to a regulated 12-V output; it delivers up to 25 A per phase or 50 A total continuous current.
LTC7890—a 100-V low Iq, dual 2-phase synchronous step-down controller—is fully optimized to drive EPC GaN FETs and integrates a half-bridge driver and smart bootstrap diode. That allows it to offer optimized near-zero deadtime or programmable deadtime and programmable switching frequency up to 3 MHz.
EPC2218—a 100 V enhancement-mode GaN FET—facilitates efficiency greater than 96.5 % for 12-V output and 48-V input. It can deliver up to 60 A continuous current and 231 A peak current, while ensuring very small switching losses at 500 kHz switching frequency.
More efficiency, less cost
The above design examples demonstrate how GaN and phase drop function combination facilitates highly efficient power conversion even at low loads. Incorporating a controller also eliminates the need for complicated DC-DC converter control software development and provides an easy and cost-effective method of driving GaN transistors.
What’s driving GaN devices into DC-DC converter design? The short answer is power density improvements. Then there’s a lower component count and smaller magnetics due to high switching frequency, which in turn leads to significantly smaller PCB area compared to silicon MOSFETs. Case in point: it allows the use of very small 1.3µH inductors. As a result, there’s a boost in energy efficiency over a wide range of loads and a reduction in the overall system cost.
There are other aspects of GaN technology that make it suitable for DC-DC conversion applications. For instance, switching capabilities of GaN transistors lead to very low input and output noise. The GaN-based converters also allow power system designers to create off-the-shelf power conversion solutions.
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