Regulated High Density Switch Capacitor Topology

Abstract:
Operating frequencies of around 100 to 200 kHz are commonly used for power of up to several kW. As frequency increases towards MHz core losses increase greatly and force designers to limit flux density. This result in larger magnetic components with more turns per windings, limiting efficiency and density improvement that used to come with frequency increase. To further increase power density in power supplies a shift from traditional inductor-based DC/DC converter to capacitor/inductor-based hybrids is happening. Capacitors are very effective at storing and transferring energy and their limitations occurs at much higher frequency than inductors. This means an increase of the upper frequency while offering higher efficiency and power density. Switched capacitor converter operate however at a constant step up/down ratio: regulation is barely possible. To achieve regulation an inductor pre or post regulator is needed. The result is a dual stage DC/DC which increase costs and impact efficiency – even if power density goes up. This paper will present a way to integrate a regulation block directly into the switch capacitor DC/DC, reducing cost and losses at the same time.