ST’s first quasiresonant ZVS 50W GaN design

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By Nick Flaherty

STMicroelectronics has launched its first 50W GaN flyback converter using quasi resonant zero voltage switching (ZVS).

The  VIPerGaN50 simplifies building single-switch flyback converters up to 50 Watts and integrates a 650V gallium-nitride (GaN) power transistor  with current-sensing and protection circuitry built into a low-cost 5mm x 6mm package.

The speed of the integrated GaN transistor allows a high switching frequency with a small and lightweight flyback transformer. Minimal additional external components are needed to design high-efficiency switched-mode power supply (SMPS).

The VIPerGaN50 is aimed at consumer and industrial applications such as power adapters, USB-PD chargers, and power supplies for home appliances, air conditioners, LED-lighting equipment, and smart meters.

The converter operates in multiple modes to maximize efficiency at all line and load conditions. At heavy load, QR operation with ZVS minimizes turn-on losses and electromagnetic emissions (EMI). At reduced load, valley skipping limits switching losses and ST’s proprietary valley lock prevents audible noise. Frequency foldback with zero-voltage switching ensures the highest possible efficiency at light load, with adaptive burst mode operation to minimize losses at very low load. In addition, advanced power management cuts standby power to below 30mW and a quiescent current of 900 µA.

The industry often turns to QR converters because of their efficiency. In traditional PWM converters, the device turns on when the voltage is at its highest, which causes power losses that are compounded as switching frequencies increase. Engineers can mitigate this with a snubber circuit, but the best way to improve efficiency is to soft-switch, meaning to switch when the voltage, or current, is at zero.

To do that, a resonant (inductor-capacitor or LC) transforms the square-shaped signal into a sinusoidal waveform. In ZVS, turn-on happens at the bottom, or valley, of the curve.  GaN is a key capability for improving the efficiency of these designs.

The VIPERGAN50 is the first member of the VIperPlus series to offer up to 50 W in a wide range of operating voltages (9 V to 23 V).  A development board with a USB-C power delivery (PD) port coming.

The VIPerGaN50 is in production now and available in a 5mm x 6mm QFN package, from $2.30 for orders of 1000 pieces. The device is in a free-sample program and can be ordered on ST eSTore.

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