GaN switch cuts adaptor size in new way

Technology News |
By Nick Flaherty

Power Integrations has developed a GaN-based switch that can dramatically cut the size of a power adaptor. This could lead to USB converters small enough to fit into wall sockets.

The MinE-CAP is multiple devices, including a gallium nitride (GaN) switch, in a package that manages the high and low voltage lines separately. This allows for lower voltage bulk electrolytic capacitor banks, slashing the size of power adaptors in the 25W to 75W by 40 percent.

“We see more demand for fast charging and larger batteries,” said Chris Lee, product marketing director at Power Integrations. “For example, Oppo ships with 65W charger that was previously used to power a laptop. The increasingly complex protocol is increasing the component count and complexity of the charger.”

“Electrolytic capacitors are physically large, occupy a significant fraction of the internal volume and often constrain form factor options – particularly minimum thickness – of adapter designs” said Lee. “The MinE-CAP IC allows the designer to use predominantly low voltage rated capacitors for a large portion of the energy storage, which shrinks the volume of those components linearly with voltage.”

This compares to reducing the size of high power adaptors using wide bandwidth semiconductors at higher frequencies which requires smaller inductors and magnetics. Instead the MinE-CAP operates at a conventional 110kHz frequency.

“MinE-CAP provides more volume saving than doubling the switching frequency, while actually increasing system efficiency,” said Lee. “The switching frequency determines the size but the line voltage determines the bulk capacitors, so a 230V input needs a 400V capacitor, twice the size of a 160V 100uF capacitor. A lot of adaptors have an input that has to accommodate the high capacitor and high voltage, so MinE CAP will give a different way of thinking about how to use the bulk capacitor.”

Next: GaN design challenges

“Above 300kHz there’s smaller magnetics but there’s more complexity in the transformer design and EMI as well as the high frequency flyback design with higher switching losses so you need and active clamp circuit with additional complexity and cost,” he added.

The MinE-CAP device also dramatically reduces in-rush current making NTC thermistors unnecessary, increasing system efficiency and reducing heat dissipation. This also reduces the need for a heat sink.

The device actively and automatically connects and disconnects segments of the bulk capacitor network depending on AC line voltage conditions. This allows designers to select the smallest high-line rated bulk capacitor required for high AC line voltages, and allocate most of the energy storage to lower voltage capacitors that are protected by the MinE-CAP until needed at low AC line. This approach dramatically shrinks the size of input bulk capacitors without compromising output ripple, operating efficiency, or requiring redesign of the transformer.

The design is particularly useful in regions where the electricity grid is unreliable such as India.

“MinE-CAP ICs are excellent for all locations with wide ranging input voltages. In India we often design for voltages from 90 VAC to 350 VAC, with a generous surge de-rating above that,” said Bhaskar Thiagaragan, Director of Power Integrations India. “Engineers here often complain about the forest of expensive high-voltage capacitors required. MinE-CAP dramatically reduces the number of high-voltage storage components, and shields lower voltage capacitors from the wild mains voltage swings, substantially enhancing robustness while reducing system maintenance and product returns.

However it is not intended for higher power adaptor designs at 75 to 100W. “Most of the 100W designs require a PFC input AC to a HV DC bus, and once that has been done there’s no need for MinE-CAP so anything above 75 W doesn’t need it,” said Lee.

The 16 pin MinSOP-16A package works alongside Power Integrations’ InnoSwitch family of power supply ICs with minimal external components and has been designed into a small adaptor with a key partner. This also opens up the possibility of one converter design that could be used worldwide and is small enough to fit into a wall socket.

Two initial design example reports (DERs) pair the MinE-CAP IC with Power Integrations’ InnoSwitch3-Pro PowiGaN IC, INN3370C-H302. A 65 W USB PD 3.0 power supply with 3.3 V – 21 V PPS output for mobile phone / laptop chargers is described in DER-626, and DER-822 describes a 60 W USB PD 3.0 power supply for USB PD/PPS power adapters using INN3379C-H302.

The MinE-CAP MIN1072M is available immediately at $1.75 for 10 Ku.

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