GaN FETs and Synchronous Rectification in 93.4% Efficient, 100-W AC-DC Reference Design

November 07, 2019 by Paul Shepard

The TIDA-01623 from Texas Instruments is a fully-tested reference design is a high-efficiency, high-power-density, ac-dc adapter solution with a wide input voltage range (100- to 240-Vac) for laptop adapters, smartphone chargers and similar applications. Synchronous rectification based on the UCC24612 helps achieve higher efficiencies. Gallium nitride (GaN) FETs are used in this design to achieve high switching frequency.

This design consists of a front-end transition-mode™ power factor correction (PFC) circuit based on the UCC28056, followed by an active-clamp flyback for isolated dc-dc conversion based on the UCC28780.

Summary of Features:

  • Wide operating input range: 100- to 240-Vac with full power delivery over entire range
  • High efficiency (93.4% peak value) with natural cooling
  • Configured as 5-V/5-A, 9-V/5-A, 15-V/5-A, or 20-V/5-A output
  • Low standby power consumption (130mW)
  • Small size (70 mm × 42 mm × 16.5 mm)
  • High power density (30 W/in3)

TIDA-01623 block diagram (click on image to enlarge)

System Description

USB Power Delivery (PD) negotiation allows devices to create a contract to deliver the optimum power level for each application under the current battery conditions. This protocol expands USB to deliver up to 100W (20V, 5A) of power. High efficiency and high power density are required for the adapter to save power and make the device easier to carry. A notebook adapter is an ac-dc converter. The block diagram above shows a typical diagram of this converter. When the output power is higher than 75W, a PFC stage is required.

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The global regulatory environment surrounding the legislation of external power supply efficiency and no-load power draw has rapidly evolved in the last decade. The newer generation power supplies need to meet multiple norms such as United States Department of Energy (DoE) Level VI standard.

This adapter reference design operates over a wide input voltage range from 100- to 240-Vac and must be able to power different equipment with different voltage demands automatically. The circuit consists of a front-end transition mode™ PFC circuit, followed by an active-clamp, flyback-based isolated dc-dc power stage. The design uses the UCC28056 controller for the PFC stage and the UCC28780 controller for the ACF stage to achieve a compact and robust control structure.

Synchronous rectification based on the UCC24612 helps achieve higher efficiencies. Gallium nitride (GaN) FETs are used in this design to achieve high switching frequency. When faults such as over-current, overpower, and over-voltage happen, the adapter reacts quickly to protect the terminal device.

This reference design is a high efficiency, high power density, 100-W output power ac-dc adapter that achieves a peak efficiency of 93.4% and a 30-W/in3 power density. The input voltage ranges from 100- to 240-Vac, and the output could be configured as 5-V/5-A, 9-V/5-A, 15-V/5-A, or 20-V/5-A outputs.

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When an over-current, short-circuit, or over-power event occurs, this adapter reference design can cut off the output and recovery automatically. With over-voltage, the adapter is latched to avoid further damage to the terminal devices. Also, this adapter meets low no-load power consumption, which is less than 130mW.

This converter operates at a high switching frequency near 500 kHz, which helps decrease the size of the transformer and capacitors. This design is fully tested and validated for various parameters such as regulation, efficiency, output ripple, startup, and switching stresses. Overall, the design meets the key challenges of adapter power supplies to provide safe and reliable power with all protections built in, while delivering high performance with low power consumption.