The dual demands for charging efficiency and device portability have driven technological innovation in compact adapters. Gallium nitride (GaN) devices, with their high-frequency switching characteristics and low-loss advantages, have emerged as the core technology to overcome the performance limitations of traditional silicon-based adapters. However, electromagnetic interference (EMI) issues arising from high-frequency switching, coupled with thermal management and reliability challenges within compact designs, remain key factors constraining the widespread adoption of GaN adapters. This paper systematically outlines the high-frequency switching advantages and EMI solutions of GaN devices in compact adapters, drawing upon practical case studies and technical data.

High-Frequency Switching

The lateral high electron mobility transistor (HEMT) structure of GaN devices endows them with gate charge (Qg) and output capacitance (Coss) values one order of magnitude lower than silicon-based MOSFETs, enabling switching speeds below 100 nanoseconds. This characteristic translates directly into three major advantages for adapter design:

Enhanced Power Density

In a 65W USB-PD adapter design, the asymmetric flyback topology utilising GaN devices elevates the switching frequency from 100kHz in traditional silicon-based solutions to 220kHz. Experimental data demonstrates that this solution achieves 94.8% peak efficiency at 90V input voltage, with a power density of 20W/in³ – a 40% improvement over silicon-based solutions. The core principle lies in high-frequency switching, which reduces the volume of magnetic components such as transformers and inductors by 60%. Concurrently, the zero-current switching (ZCS) in the synchronous rectification circuit further minimises losses.

Dynamic Response Optimisation

Application cases in drone motor drivers demonstrate that GaN devices, supporting switching frequencies above 100kHz, reduce motor speed control response time to under 5ms – a threefold improvement over silicon-based solutions. This dynamic performance proves equally critical in adapter load surge scenarios, such as when a mobile phone transitions from standby to fast-charging mode. GaN devices ensure output voltage fluctuations remain within ±1%.

Thermal Efficiency Breakthrough

Although GaN devices exhibit slightly lower thermal conductivity than silicon, their on-resistance per unit area is reduced by 70% compared to silicon-based components. In a 45W adapter design, combining a 0.15mm thick copper substrate with GaN devices lowers thermal resistance from 5℃/W to 2.5℃/W, maintaining junction temperatures below 125℃ even under high ambient conditions.

I. EMI Challenges

GaN devices exhibit a dv/dt (voltage slew rate) exceeding 50V/ns—over five times that of silicon-based devices—giving rise to the following EMI issues:

Conducted Interference Surge

At a switching frequency of 200kHz, GaN adapters generate differential-mode interference reaching 60dBμV in the 1MHz band, exceeding the CISPR 32 standard limit by 10dB. This stems from high-frequency current loops coupling with the parasitic inductance of PCB traces, forming common-mode interference paths.

Radiated Interference Propagation

Testing of a laptop adapter revealed that GaN solutions exhibit 15 dB higher radiation intensity than silicon-based solutions in the 300 MHz band. This primarily originates from near-field coupling caused by voltage ringing at the switching node. Such interference may disrupt 2.4 GHz band communications of nearby Wi-Fi devices.

Sensitivity to Parasitic Parameters

GaN devices exhibit extreme sensitivity to PCB layout-induced parasitic inductance. Experiments demonstrate that a mere 0.5nH of parasitic inductance in the drive loop can increase switching losses by 20% while generating 5V overshoot voltage, jeopardising device reliability.

II. EMI Suppression

Addressing high-frequency EMI in GaN adapters requires a three-pronged solution encompassing driver design, PCB layout, and shielding techniques:

Dynamic Impedance Drive Technology

Employing a gate driver with adjustable output impedance provides a low-impedance path during GaN device turn-on to accelerate gate voltage rise. It switches to high impedance near the threshold voltage to suppress current overshoot. In a 65W adapter case study, this technology reduced turn-on losses by 32% while controlling the driver signal's dv/dt within 30V/ns, effectively suppressing radiated interference.

Multi-layer PCB Layout Optimisation

A four-layer PCB stack design reduced the drive loop area to under 10mm², lowering parasitic inductance from 3nH to 0.8nH. Key measures included:

- Differential traces with 0.1mm width and 0.2mm spacing to mitigate common-mode interference;

Laying 0.2mm thick copper foil between the switch node and ground to form distributed capacitive filtering;

Positioning input filter capacitors near power pins to shorten high-frequency current paths.

Integrated Shielding Solution

Encapsulating GaN devices and driver circuits within a single IC, utilising 3D stacking technology to minimise drive paths. A manufacturer's InnoSwitch3 series employs InSOP-24D packaging, reducing drive loop parasitic inductance below 0.5nH. Concurrently, integrated FluxLink inductive coupling feedback eliminates EMI radiation from optocouplers. Test data indicates this approach reduces conducted interference by 12dB at 1MHz.

Slew Rate Control and Waveform Shaping

Introducing a slew rate control circuit into the drive signal extends the gate voltage rise time from 10ns to 30ns, reducing dv/dt from 50V/ns to 15V/ns. Combined with the filtering function of the pre-driver circuit, this technology achieves an overall 18dB reduction in system EMI radiation intensity across the 30MHz-1GHz frequency band, meeting CISPR 32 Class B standards.

III. Typical Applications

USB-PD Adapter

A 65W GaN adapter from a certain brand employs an asymmetric flyback topology, achieving 93% full-load efficiency at a 220kHz switching frequency. Through dynamic impedance drive and multilayer PCB layout, it passed CISPR 32 standards on the first attempt during EMI testing, with a 40% reduction in volume compared to silicon-based solutions.

Drone Motor Drive

In quadcopter drones, GaN inverters supporting 100kHz switching frequencies elevate motor efficiency to 96%. Their compact design (measuring merely 8cm × 5cm × 2cm) directly benefits from GaN devices' high-frequency characteristics, whilst integrated shielding solutions maintain radiated interference within regulatory limits.

Server Power Supply

A 1200W server power supply for a data centre utilises 1200V/80mΩ GaN devices, achieving 98% peak efficiency at a 200kHz switching frequency. Through slope control technology and multi-layer magnetic shielding design, its EMI levels are reduced by 25dB compared to silicon-based IGBT solutions, meeting stringent industrial environment standards.

V. From Device Optimisation to System Integration

As GaN device costs continue to decline, their applications are expanding beyond consumer electronics into automotive electronics, photovoltaic inverters, and other sectors. The EPC23102 integrated power IC, released in 2025, integrates GaN devices, driver circuits, and protection functions within a 3mm×3mm package, supporting a 1MHz switching frequency. This marks GaN technology's advancement towards higher integration. Concurrently, AI-driven EMI prediction models enable real-time optimisation of driver parameters, reducing adapter design cycles from months to weeks.

The application of GaN devices in compact adapters represents a fundamental technological revolution in high-frequency operation and integration. Through system-level solutions such as dynamic impedance drive, multilayer PCB layout, and integrated shielding, GaN adapters have successfully overcome EMI bottlenecks, achieving comprehensive enhancements in efficiency, density, and reliability. As third-generation semiconductor technology matures, GaN will become the core driving force behind the miniaturisation and high efficiency of power electronic systems.