New GaN Power Supply IC Delivers Up to 85 Watts Without Heatsink

November 02, 2023 by Duane Benson

Power Integrations has unveiled the so-called "world’s highest-voltage, single-switch GaN switch-mode flyback power supply integrated circuit".

Power Integrations has released the newest member of its flyback switch mode power supply (SMPS) integrated circuit family. The InnoSwitch3-EP 1,250-V chip uses gallium nitride (GaN) to achieve a 1,250-V maximum input at up to 93% efficiency. 


InnoSwitch3-EP flyback switcher IC

InnoSwitch3-EP flyback switcher IC for high-efficiency applications. Image used courtesy of Power Innovations

Conventional silicon (Si) MOSFET-based SMPS generally top out at 90% efficiency. While 90% to 93% efficiency may not seem like a significant gain, it reduces losses by a third. Any reduction in losses is significant since those losses dictate the need for expensive cooling, heat sinking, and overall power supply size.

When used as the primary switching transistor, the new high-voltage PowiGaN switch increases frequency switching, which means smaller passive components. 


Primary controller block diagram

Primary controller block diagram. Image used courtesy of Power Integrations

GaN has higher thermal tolerance and lower resistance-caused losses to heat, both of which reduce the need for heat sinking. The InnoSwitch3-EP (datasheet linked) also combines both primary-side and secondary-side controllers in the same chip to reduce the overall parts count.


Secondary controller block diagram

Secondary controller block diagram. Image used courtesy of Power Integrations

In the InnoSwitch3 chip, the primary and secondary sides communicate internally. The end result is a smaller, more efficient power supply.


Fully-Manufacturable Reference Design

Along with the new IC family, Power Integrations released a reference design for an AC power supply with 60-W continuous output power and a 12-V wide input range (90–480 V). The reference design includes complete specifications, a bill of materials (BOM), a schematic diagram, a two-layer printed circuit board (PCB) layout, and detailed transformer winding instructions. The power supply board measures 1.80” x 4.24”.


Typical application schematic

Typical application schematic. Image used courtesy of Power Integrations

The design package comes with test and evaluation data, design notes, and operational descriptions of the InnoSwitch3 IC. Most impressive is the thorough documentation for the transformer construction, including wiring diagrams, cut-away views, and a complete set of in-process photographs.

For fully custom designs, Power Integrations also offers PI Expert, an online power supply development tool. PI Expert jumpstarts the power supply design process for the new GaN devices and silicon-based chips.


Big Gains Through Lower Losses

The ideal transistor switch would simply turn current flow on or off with current or voltage on the gate with no losses. However, in the real world, transistors have an impedance known as on-state drain-to-source resistance (RDS(on)) that draws current when on. Capacitance charge (Coss) collects when the switch is off. The capacitance then discharges when the device is switched on. In a conventional MOSFET, as the silicon die size goes up, RDS(on) goes down and Coss goes up. Those counter-productive characteristics ultimately limit silicon MOSFET efficiency.


Advantages of GaN

Doug Bailey, Power Integrations' VP of marketing, details the advantages of GaN. Image used courtesy Power Integrations

GaN delivers both lower RDS(on) and lower Coss, increasing efficiency, reducing heat, and increasing switching frequency. The end result is a more capable power system of the same size or an equivalently capable system in a smaller and lighter size.


Power Integrations Reaches for Best-in-Class Voltage

Power Integration released its first GaN-based power IC in 2019 and has continued to improve GaN performance since then. Early in 2023, it introduced a 900-V version, and now, with the 1250-V version, the company claims the best-in-class voltage capability. At an industry-standard 80% de-rating from the absolute maximum, designers can now access 1,000-V peak-rated power supplies.

The GaN parts are complemented by a complete line of integrated circuits for motor control and power supply applications. The full InnoSwitch3 product line of SMPS chips includes options in silicon up to 750 V, silicon carbide up to 1,700 V, and the newest GaN with a 1,250-V absolute maximum rating.