Delivering Efficient Power Control with Discrete Gallium Nitride (GaN) Devices

Introduction

Selecting the right power control components is important to accommodate operational differences, as nearly every type of device or class of devices has different power capabilities. Traditionally, power transistors that regulated currents and voltage levels have been based on silicon (Si) or silicon carbide (SiC) materials. However, as power needs change, so does the demand for greater efficiency. Gallium nitride (GaN) is an emerging semiconductor material, proving its ability to provide increased power density and efficiency with lower loss levels when used for middle power and voltage (100 V–600 V) applications.

Image used courtesy of Adobe Stock

When combined with a high electron mobility transistor (HEMT) design, GaN provides increased performance in middle-voltage, high-frequency applications. These applications include server power supplies for data centers, base station power supplies, on-board electric vehicle chargers, and consumer AC adapters for phones, tablets, and other compact electronics. Among these is ROHM’s EcoGaN™ HEMT lineup of discrete TO-Leadless (TOLL) packages, offering excellent thermal performance and high-power density for data centers, base stations, and photovoltaic inverters.

The Range of Power Control Transistors

The power and operating frequency bands of electronic systems vary depending on the device’s intended application and configuration. These variations often occur within the same equipment. For example, electric trains operate at voltages between 600 V DC and 25,000 V AC, while electric car chargers range from a slow-charging 120 V home charger to a public DC fast-charging station operating at 480 V. The power transistors controlling these devices come in numerous semiconductor switch models, including:

• Field-effect transistors (FETs): FETs use an electric field to regulate the flow of current through a channel. They require very little power to operate, making them ideal for battery-powered devices.
• Metal-oxide-semiconductor field-effect transistors (MOSFETs): This type of FET is controlled by the application of voltage to an insulated gate electrode. They offer efficiency, low power use, and low resistance in a range of devices.
• Schottky barrier diodes (SBDs): Named after German physicist Walter H. Schottky, these use a junction of metal and an n-type semiconductor instead of a traditional p–n junction to create a fast switching and a low forward voltage diode.
• Insulated gate bipolar transistors (IGBTs): IGBTs use a power switch that has four alternating layers and a metal-oxide-semiconductor gate structure to provide low power dissipation, fast switching speeds, and high voltage capabilities. They are often used in large, high-power equipment.
• GaN HEMT: This newer type of transistor is made from GaN and has a high-mobility electron channel that is essentially a fast and efficient power-switching device with high breakdown voltage capabilities.

Many of these transistors traditionally come in both Si and SiC versions, such as the ROHM family of SiC SBDs for 650V–1700V ranges and the ROHM Si-based Power MOSFETS for 190 V–800 V applications. GaN HEMT complements the applications of these traditional material-based devices. As a result of GaN HEMT’s higher efficiency, thermal conductivity, and switching speeds, it could serve as a replacement for Si and SiC in certain circuits that have middle to high voltage requirements and are designed to operate at very high switching frequencies.

Gallium Nitride (GaN) complements Silicon and Silicon Carbide (SiC) in power device applications, and will likely even replace both for some middle power and voltage and high frequency uses.

The Application Benefits of GaN Technology

GaN is a hard and stable synthetic material made with gallium and nitrogen atoms. It has higher thermal conductivity and density than the naturally occurring silicon element, and allows for high electron mobility and fast switching speeds. Additionally, GaN’s wider bandgap than silicon makes it ideal for use in power semiconductors as it can support high voltages with a much smaller blocking distance.

GaN can emit a blue light while in use. For this reason, it has been used for several decades in light-emitting diodes (LEDs) and in the lasers that read Blu-ray discs. Over time, the benefits of GaN led to its use in transistors in X-ray and MRI machines, solar panel systems, radio frequency components, lasers, radio frequency devices (e.g., military radars), photonics (e.g., visible light communication systems), consumer devices (e.g., USB-C adapters and chargers), and more.

However, GaN HEMT represents a step forward over the conventional design of GaN transistors. With a high electron mobility structure, GaN HEMT is able to increase the already fast switching speeds and strong power, thermal, and efficiency capabilities associated with the material. GaN HEMT can also operate at higher frequencies and have a high power density, which helps substantially reduce the size of high-power Si- or SiC-based systems.

There are a number of GaN-based solutions available for power control semiconductors. For example, ROHM’s 650V lineup of EcoGaN products includes all-in-ones with built-in drivers and controllers, power stage transistors with integrated gate drivers, isolated or one- or two-channel drivers, or single and discrete transistors. These varying solutions come in different packages, including:

• Dual-flat no-leads (DFN) packages are used to connect integrated circuits to printed circuit boards
• TO-Leaded top-side (TOLT) cooling packages
• TOLL packages, which offer space savings in high-current applications

Fast-Switching, High-Thermal-Performance Discrete EcoGaN Solutions from ROHM

ROHM’s lineup of discrete EcoGaN products offers class-leading performance, reliability, and safety. Notably, the products feature built-in circuits providing Human Body Level Class 2 electrostatic discharge protection, and they have one of the industry’s lowest dynamic on-resistance (Ron). In addition, the molded form factor, zero reverse recovery time, and a high switching speed of > 1 megahertz (MHz) make these discrete solutions ideal for AC adapters across applications—including smartphones, tablets, cameras, televisions, personal computers, office equipment, air conditioners, refrigerators, washing machines, vacuums, and more.

ROHM’s lineup of TOLL-based discrete GaN HEMT solutions are best-suited for the critical task of controlling power in data center equipment, wireless base stations, and photovoltaic (solar) inverters.

For example, the GaN 650V TOLL - GNP20XXTD-ZE2 lineup series of discrete EcoGaN solutions is now available with the following features:

• Drain-source voltage (VDS) of 650V
• Normally off (enhancement mode)
• Built-in electrostatic discharge protection
• SMD package
• Fast switching
• Zero reverse recovery

Powering the Future of Technology

Though Si- and SiC-based transistors are likely here to stay for the foreseeable future, GaN will play an increasingly larger role in the control of electrical power. GaN’s power density, energy efficiency, and faster switching speeds make it anticipated to replace both Si and SiC transistors in certain products and use cases, providing system designers with another reliable, safe, and high-performance semiconductor material. ROHM’s advanced line of efficient EcoGaN solutions, including the GaN 650V TOLL - GNP20XXTD-ZE2 series of discrete transistors, delivers on this promise now.

To learn more, please visit rohm.com or contact your local sales representatives.

This Industry White Paper was written by Ming Su, ROHM Semiconductor.