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Power Integrations / MinE-CAP

Space Savings on DC Bus Capacitors

28. Oktober 2020, 15:00 Uhr   |  Ralf Higgelke

Space Savings on DC Bus Capacitors
© Power Integrations

With the MinE-CAP, Power Integrations presents an IC that reduces the volume of power adapters up to 70 W by up to 40 percent.

The DC link capacity in a flyback converter is determined by the worst case, i.e. at minimum input voltage. However, this is oversized for the typical case. With the MinE-CAP, Power Integrations presents an IC that reduces the volume of power adapters up to 70 W by up to 40 percent.

Smartphone and tablet chargers usually use a wall power adapter. And of course these should become smaller and smaller. The conventional approach is to increase the switching frequency. This allows reducing the size of the transformer. But this can only be used to a certain extent because of the EMI emissions and waste heat.

Another bulky component in a power adapter is the DC bus capacitors. Their capacitance depends on the required hold-up time at minimum input voltage. This means that under typical conditions much less capacitance would be sufficient at high voltage (E = ½ CU²). If charged electrolytic capacitors with a low nominal voltage could be added at low input voltages, space could be saved because the volume of these components scales linearly with voltage.

Capacity on demand

This is the underlying idea behind MinE-CAP, a new type of IC from Power Integrations. The device utilizes the small size and low RDS(on) of the company's gallium nitride transistors (PowiGaN) to actively and automatically connect and disconnect segments of the capacitor network depending on line voltage conditions. Designers using MinE-CAP select the smallest high-voltage 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. Moreover, the MinE-CAP significantly reduces the inrush current due to the lower input capacitance thus eliminating the need for NTC thermistors. This increases system efficiency and further reduces waste heat. The MinE-CAP IC achieves just as significant overall power supply size reduction as increasing the switching frequency, while using fewer components and avoiding the challenges of higher EMI and the increased transformer/clamp dissipation challenges associated with high-frequency designs.

However, the MinE-CAP will only be useful for power adapters up to 70 W, which do not need to include a PFC stage - for example, USB PD chargers up to 65 W.

MinE-CAP from Power Integrations

Power Integrations, MinE-CAP
Power Integrations, MinE-CAP
Power Integrations, MinE-CAP

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Chris Lee, Product Marketing Director of Power Integrations, comments: "MinE-CAP offers more volume savings than doubling the switching frequency, while actually increasing system efficiency."

Bhaskar Thiagaragan, Director of Power Integrations India, emphasized: "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. 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.”

Housed in the miniature MinSOP-16A package, the new devices work seamlessly with Power Integrations’ InnoSwitch family of power supply ICs with minimal external components. MinE-CAP MIN1072M ICs are available immediately from PI offices and franchised distributors and are priced at $1.75 for 10 Ku.

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.

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