“Enhancement-mode GaN is indeed a single-chip normally-off device. However, in order for enhancement-mode GaN transistors to function properly in all operating modes, many passive components are required, and sometimes active devices (such as MOSFETs) are required.
Transphorm, the agency brand of Kaga Fuyi Electronics, is a company dedicated to the design, manufacture and sale of high-performance, high-reliability gallium nitride (GaN) semiconductor power devices for high-Voltage power conversion applications. The wide range of products used has enabled Transphorm to accumulate a lot of questions and feedback from users. Here we share a question about “enhancement-mode devices and dual-chip normally-off GaN FETs” for your reference in product use~
Are enhancement mode devices better than two-chip normally-off GaN FETs?
ZJ Answer: Currently, there are two device options for high-voltage GaN power conversion – enhancement mode and two-chip normally-off GaN FET (below). There is a misconception in the industry that only enhancement devices are viable and practical in design. This misunderstanding leads to confusion when choosing the right power device for a particular product.
Physical structure of two-chip normally-off GaN FETs and enhancement-mode GaN devices
In fact, what end product manufacturers need to evaluate is how different types can take advantage of the comprehensive value that GaN technology can bring. When using the wide bandgap semiconductor material gallium nitride in the power system, it is necessary to comprehensively consider whether the system design can give full play to the four inherent value advantages of GaN devices, namely:
faster switching speed
higher power density
better thermal performance
Greater power efficiency at lower overall system cost
A known advantage of gallium nitride is that it switches faster than traditional silicon devices, and at the same time, it can help eliminate a loss-generating component. This advantage is even more pronounced for a bridge rectifier with a bridgeless totem-pole power factor correction configuration. This typically results in higher efficiency, which results in smaller system size and lower overall system cost.
Enhancement-mode GaN is indeed a single-chip normally-off device. However, in order for enhancement-mode GaN transistors to function properly in all operating modes, many passive components are required, and sometimes active devices (such as MOSFETs) are required.
Driving an enhanced device requires additional gate circuitry, protection, and startup circuitry, increasing the chance of failure, contrary to its perceived simplicity.
In contrast, two-chip normally-off GaN FETs do not have such a requirement. It requires a low number of external components and can be used with off-the-shelf drives, reducing complexity and associated costs to ZD.
It is also important to note that many enhancement devices are available in surface mount packages only.
Of course, these packages can find corresponding applications.However, as power levels increase, this introduces new design and thermal issues, as high-power applications require multiple boost devices to be used in parallel, increasing the number of components and printed circuit boards[PCB]the cost of the entity.
When assessing the high volume manufacturability of power supply equipment, the packaging issues of enhancement mode devices can sometimes cause some trouble, and this should be taken into account when deciding on the type of GaN device to be used. Two-chip normally-off GaN FET devices can also be designed in standard 3-pin TO-XXX packages or surface mount packages (for low power and high board-level assembly density applications).
TO-XXX packages are well known in the component market and have been used for decades. It is easy to install, dissipates heat, and a single device can be used in applications up to several kilowatts.