Efficient 65W USB-C design with lower temperatures and integrated half-active bridge

Pulsiv Limited has released the world's most efficient 65W USB-C GaN-optimised reference design to meet the complex challenges associated with thermal performance in power supplies. This ground-breaking and highly anticipated development will revolutionise the USB-C fast charging space by providing a unique combination of features and benefits not seen in other designs.

The PSV-RDAD-65USB reference design combines the company's OSMIUM technology with an industry-standard QR flyback and highly optimised, ultra-compact magnetics. It is the first in a series of designs aimed at pushing the boundaries of power conversion by greatly lowering operating temperatures, minimising losses, and lowering size to create a sustainable platform for the USB-C standard.

Pulsiv's chief product officer, Dr Tim Moore, has been managing the development of this design and comments: "Our mantra has always been focused on developing solutions that 'do more while using less', and this design demonstrates how Pulsiv OSMIUM technology can deliver fast charging without the associated complexity of managing high temperatures. The demand for more power and faster charging of cordless products is rapidly increasing, impacting everything from mobile phones to power tools. This means more power is needed in a small form factor, which is even more critical when developing in-wall/desk solutions that are sensitive to heat. With 30% lower component temperatures, no inrush current, and high efficiency, we enable designs to become safer, smaller, and be more reliable."

Compared to other designs, the reference design demonstrates a significant improvement in thermal performance and reduces critical component temperatures by more than 30%. At full load, the flyback transformer reaches an impressive 33.9C at 230VAC and 30.3C at 265V above an ambient temperature of 26.1C. This remarkable achievement is likely to set a new benchmark and enable 65W fast charging in space-constrained environments and/or heat-sensitive applications such as in-wall plug sockets that incorporate USB-C connectivity.

This technology senses AC line voltage and frequency to adjust capacitor charging time, therefore the circuit draws no line current at the AC zero voltage crossing. This allows a simple half-active bridge implementation to increase efficiency, particularly at low-line conditions. MOSFETs in the lower half of the AC to DC bridge are carefully controlled and combined with high-side diodes. The half-active bridge in this design strikes the delicate balance between efficiency, cost, and complexity and supports universal input with efficiency gains of 0.7% at full load from a 115VAC supply.

The technology generates an HVDC output that varies between the peak AC input and 150V to drive the QR flyback at maximum efficiency. The wider voltage range greatly lowers primary side inductance to allow the use of an EQ20 transformer, which was developed in partnership with magnetics experts, Frenetic. Their CEO, Chema Molina, comments: "Our team of magnetics experts have demonstrated that Pulsiv OSMIUM technology maximises efficiency and reduces the size of the flyback transformer to a level we've not seen before. This significant development will enable customers to improve performance, reduce size, and lower the cost of their design, and we're excited to be part of such an innovative solution.

"This results in a 20% size reduction and 50% efficiency improvement compared to an RM8 core typically used in other designs."

GaN transistors from Innoscience have lowered the RDSon and parasitic capacitance to decrease losses and optimise cost in the flyback and synchronous rectifier sub-systems.

General manager for Innoscience EMEA, Denis Marcon, adds: "We've demonstrated that GaN technology is perfectly suited to increasing efficiency, reducing losses, and optimising cost but Pulsiv OSMIUM technology adds further benefits by significantly improving the overall performance and reducing energy waste. Their technology is truly game-changing, and I'm delighted that Pulsiv has chosen to incorporate Innoscience GaN devices in this reference design."

The PSV-RDAD-65USB document package, including a datasheet, schematics, BoM, and Altium files, can be downloaded from the Pulsiv website.