April/May 2021

28 POWER SUPPLY DESIGN www.power.com/products/MinE-CAP Issue 2 2021 Power Electronics Europe www.power-mag.com Novel GaN Design Reduces Volume of AC/DC Converters Substantially Power Integrations recently released a GaN-based IC 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. Andy Smith, Product marketing manager at Power Integrations discusses this new GaN application in detail. 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. Intelligent approach to reduce the size The MinE-CAPTM IC dramatically shrinks the size of input bulk capacitors without compromising output ripple, operating efficiency or requiring redesign of the transformer. When compared to traditional techniques such as very high switching frequency operation, MinE-CAP achieves the same or greater overall power supply size reduction whilst avoiding the challenges of complex EMI filtering and the increased transformer/clamp dissipation associated with very high frequency Figure 1: MinE-Cap typical application schematic Figure 2: Typical component value ranges for optimal space saving and converter operation