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Power GaN Reduces Volume of AC/DC Converters Sustantially

Power Integrations released on October 28 a GaN-based switch called MinE-CAP, intended for use in a new generation of mobile credit card-sized chargers or offline power supplies. By halving the size of the high-voltage bulk electrolytic capacitors required in offline power supplies, this IC enables a reduction in adapter size of up to 40 %. The device also reduces in-rush current making NTC thermistors unnecessary, increasing system efficiency and reducing heat dissipation. The principle sounds easy – a smaller electrolytic capacitor can be used in parallel to the input bridge rectifier and the MinE-CAP adds a second capacitor during the rectified half waves in order to release energy for the flyback converter – preferably a GaN-based Innoswitch-3. MinE-CAP is connected in series with the second capacitor and switches is on when necessary in correspondence with the flyback IC. In other words, the MinE-CAP leverages the small size and low on-resistance of PowiGaN™ transistors to actively and automatically connect and disconnect segments of the bulk capacitor network depending on AC line voltage conditions. By using MinE-CAP the smallest high-line rated bulk capacitor required for high AC line voltages can be selected, and most of the energy storage can be allocated to lower voltage capacitors that are protected by the MinE-CAP until needed at low AC line. This approach drastically shrinks the size of input bulk capacitors without compromising output ripple, operating efficiency, or requiring redesign of the transformer.

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. “The MinE-CAP IC allows the designer to use predominantly lower voltage rated capacitors for a large portion of the energy storage, which shrinks the volume of those components linearly with voltage. USB PD has driven a major market push towards small 65 W chargers and many companies have concentrated on increasing switching frequency to reduce the size of the flyback transformer. MinE-CAP provides more volume saving than doubling the switching frequency, while actually increasing system efficiency,” comments Product marketing manager Andy Smith.

Housed in the miniature MinSOP-16A package, MinE-CAP devices work seamlessly with flyback InnoSwitchers with only two external resistors. MinE-CAP MIN1072M ICs are available now at $1.75 (GaN for low on-resistance) for 10 Kunits. Two initial design example reports (DERs) pair the MinE-CAP IC with 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.

DER-626 demonstrates the high power density and efficiency that can be attained due to the high level of integration of the InnoSwitch3-Pro controller and total volume reduction due to the MinE-CAP family of ICs. The MinE-Cap is used to minimize the physical size of the input bulk capacitors and, together with the use of low-profile planar magnetics, a form factor of 82 mm (L) x 51 mm (W) x 12 mm (H) without an enclosure corresponding to a power density of 21.22 W/in³ is realized. DER-822 demonstrates the high power density, exceptional performance, and high efficiency designs possible when the InnoSwitch3-Pro family of controllers is paired with the input capacitor volume-reduction capabilities of the MinE-CAP IC.

An other application for MinE-CAP are electrical distribution networks with unstable voltages. “In India we often design for voltages from 90 VAC to 350 VAC, with a generous surge de-rating above that. Engineers here often complain about the forest of expensive high-voltage capacitors required. MinE-CAP 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,” adds Bhaskar Thiagaragan, Director of Power Integrations India. AS



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