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Custom RISC-V core for AC-DC power controller

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By Nick Flaherty


Eggtronic in Italy has launched the first in a series of highly integrated AC-DC converter technologies for simpler, higher efficiency chargers based around a customised RISC-V processor core.

“The QuarEgg technology was born to address the issues from quasi resonant and active clamp technologies,” said Igor Spinella, CEO and founder of Modena-based Eggtronic. This uses Zero Voltage Switching (ZVS) across the whole load, boosting the efficiency for chargers up to 45W.   

“Then Q1 next year we will launch SmartEgg which is a single stage power factor correction (PFC) and power converter. Then there is the next one, ClassEgg, the longer term architecture to mimic class E operation which is a fully resonant architecture for higher power and when the load is always 50 percent above the nominal voltage.”

The single chip handles all three modes with different pinouts. “It’s the same chip with different configuration,” said Spinella. “We change the number of pins in the package but the chip has the full capability for PFC. We have in our roadmap a chip with higher performance.”

The RISC-V digital core from the Open Hardware Foundation is customised with extensions for the power conversion architecture. “It’s not exactly built from scratch but we have used extensions for optimisations,” he said. “The extensions are for our use and we are developing a complete environment for power conversion algorithms with ways to develop the control algorithms.”

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QuarEgg+ is the first in a series of power conversion architectures that make up the Eggtronic EcoVoltas family and provides efficiencies are up to 95% at full load and up to 92% at light load.

“Quaregg is based on the secondary side controller that takes care of everything,” said Spinella. “Compared to Quasi-resonant architectures we are able to ensure ZVS in every conditions from 1 percent of load to full load, avoiding the need for a burst mode. Controllers using active clamp are good at higher power close to full load but can be variable down at light loads so we remove the high side high voltage MOSFET that is expensive and not easy to design with. This means you can derate the secondary side MOSFET from 100V to 60V and with better EMI you can reduce the size of the filters and the size of the charger.”

“Using the same silicon MOSFET and switching architecture, the same magnetic core and just changing the controller to our technology gives an increase from 91 to 93 percent efficiency from 5 to 45W,” he said. “This is with the same cost as QR and 30 percent cheaper than an active clamp design as you can reduce the cost of the primary side MOSFET and the filters,” he said.

With existing silicon devices and an RM8 magnetic core, the design has a power consumption of 15mW at low load at 115V and 28-30mW with 240V. Moving to gallium nitride gives a further efficiency boost.

“Moving to GaN gives another 0.5 to 1 percent depending on the output power and switching frequency. The controller can go up to 1MHz with high resolution timers that we designed to be future proof,” he said.

“We always try to help the customer, we hit 25W/in3 at 100kHz, Because of this we always try to understand the specification and select the lowest frequency to meet the performance. In that case selecting a Gan FET with lower parasitic capacitance for higher frequency means we are able to work at 300 to 400kHz and hit 25 to 27W/in3 and use a planar transformer to take full advantage of higher frequency,” he said.

The isolation barrier between the primary and secondary side is a key issue for the controller and this handled in different ways depending on the customer requirements. “The controller is compatible with three ways to transfer the driving signal, an optocoupler, capacitive and we also have a signal transformer that is extremely small.”

Eggtronic will be offering both GaN-based and silicon-based QuarEgg+ products with power outputs of 35 W, 45 W and 60 W. Output options include USB PD, fixed voltage and CC CV. Development boards, integrated power controllers, a range of proprietary magnetic components and comprehensive technical support will also be available as well as support for manufacturing.

“There are selected companies that ask us to help with mass production and we offer mass production through CEMs and assembly companies that we like to use we have Taiwan, China and a European contract manufacturer – there is a lead Italian customer and the CEM is European,” he said.

The controller is currently built in a 180nm process at TSMC. “This is not the only possible partner and we are exploring other partners. Scaling to under 90nm, 65nm is a possible choice, we have not decided yet as it is about availability of the process. We can halve the price of the chip without cutting down the performance by scaling the digital part which is most of the area of the chip and that gives cost optimisation,” he said.

The company is currently working with OEMs and will look at distribution at the end of next year, says Spinella.  

“Distribution is in the roadmap but at the moment we prefer to find selected key customers to ramp up the volumes and then ramp up the volumes and then the price will be available,” h said. “At the end of 2022 when the first customers are already in mass production its easier to put a version into distribution of some versions of our chip,” he said.

www.eggtronic.com

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