STMicroelectronics Debuts 50 W GaN Converter for High-efficiency Power Applications
The company’s new converter is a quasi-resonant (QR) flyback controller incorporating 650 V E-mode GaN transistors.
The VIPerGaN50, which STMicroelectronics (ST) announced at the Applied Power Electronics Conference 2022 (APEC 2022) last week, enables designers to leverage GaN wide-bandgap (WBG) technology to satisfy today’s increasingly stringent efficiency requirements.
GaN semiconductors are far more power-efficient than last-generation silicon (Si) devices, and their high switching speeds allow for a much lighter and smaller flyback transformer, making for a final product that is both cheaper and more compact.
The VIPerGaN50 is the first member of ST’s VIPerPlus series to incorporate a GaN transistor. Image used courtesy of STMicroelectronics
The versatile VIPerGaN50 changes its mode of operation in response to constantly fluctuating line and load conditions, to deliver greater energy efficiency. What’s more, the device’s highly integrated nature makes it possible to design a small, highly efficient switched-mode power supply (SMPS) with far fewer external components.
Old-school pulse width modulation (PWM) converters turn on when voltage is at its highest. This is not only inefficient, but is also a potential source of electronic noise.
Zero-voltage switching (ZVS) devices, instead, take advantage of “soft switching,” and turn on when the current or voltage is at zero. This is made possible first by a resonant (inductor-capacitor, or LC) that serves to transform a pulsating DC signal into a sinusoidal waveform. Next, the low-point, or valley of the new waveform is detected. That valley is where turn-on finally takes place, and because switching occurs when power is essentially off, maximum efficiency is attained.
The VIPerGan50 is itself capable of zero-voltage switching, amongst other operation mode features, which we explain in further detail below.
Multi-Mode Operation to Optimize Performance
VIPerGaN50 has the ability to automatically adapt its switching frequencies and methodologies in response to output demands.
Under heavy output loads, the device will automatically operate in QR mode, with zero-voltage switching. The quasi-resonant circuit causes the device to turn on in step with transformer demagnetization.
Valley skipping is a mode, activated at medium loads, in which there is not a turn-on at every low-point. In essence, switching frequency is decreased. This minimizes losses.
Frequency foldback mode with zero-voltage switching, activated under light loads, also reduces frequency. Still, beyond a certain point, audible noise can be generated. To avoid that pitfall, frequency foldback ensures the frequency does not pass the critical threshold point.
The various operational modes of the VIPerGaN50. Image used courtesy of STMicroelectronics
Burst mode comes into play at very light loads or during no-load conditions. Here, the switching frequency might be reduced to only a few hundred Hz, while maintaining a constant peak current. Because this current is very low, any sound generated, even if the frequency is within human audible range, will be at an amplitude too low to be detected.
In this mode of operation, the VIPerGaN50 can consume fewer than 30 mW, with a quiescent current of 900 µA. That’s significant, as low current consumption during “off” times is a prime target for present and emerging international standards.
Each of the VIPerGaN50’s protection features automatically allows the device to reactivate if and when a hazard subsides. These protections include:
- Output overvoltage protection
- Overpower protection (OPP variation)
- Input overvoltage protection
- Thermal shutdown
- Power adapters
- USB-PD chargers
- Power supplies for:
– Air conditioners
– LED-lighting equipment
– Smart metering
The VIPerGaN50 is available in a 5 x 6 mm QFN package