A Resonant Cockcroft-Walton Switched-Capacitor Converter Achieving Full ZCS and >10kW/inch³ Power Density

Abstract

Hybrid LC switched-capacitor converter architectures have demonstrated high power density while retaining efficiency at high conversion ratios. This work presents a resonant Cockcroft-Walton (CW) converter that achieves full zero-current switching (ZCS) on all switches using a single inductor and requiring only one current sensor. To do so, an Nphase clocking scheme is employed, eliminating the parallel paths that typically introduce transient shorting losses in a conventional 2-phase CW converter. The reduced voltage stress on the CW's fly capacitors results in a dramatic reduction in volume when using common MLCC capacitors. A discrete 1:5 CW prototype using silicon FETs and a spiral trace inductor was assembled on two commonly available PCB processes: 0.8 mm FR4 with 2 oz. Cu, and 0.127 mm polyimide film with 0.75 oz. Cu. The latter achieved a peak efficiency of 95% and a maximum power density of 0.686 W/mm 3 (11.2 kW/inch 3 ) in a volume of 44.5 mm 3 (0.00271 inch 3 ), excluding level-shifting and clock generation circuits.

A Resonant 1:5 Cockcroft-Walton Converter Utilizing GaN FET Switches with N-Phase and Split-Phase Clocking

“…Since there is only ever one active voltage loop that includes the inductor, all switches experience ZCS. As discussed in [12], the same current sensing hardware, placed in series with the inductor, can be reused for all N phases, simplifying design and potentially reducing quiescent current draw when compared with the multiple sensors required for the Split-phase scheme discussed in [13] and in part B here. Fig.…”

“…When compared with [5], the most similar prior work, this prototype achieves a 49% increase in select component volume power density despite a larger conversion ratio at reduced voltage, with roughly equivalent thermal dissipation density (<9% increase). This is likely in large part due to the reduced voltage stress of the CW structure being used in place of the Dickson, as discussed in [12].…”

“…Specifically, the Cockcroft-Walton (CW) is selected (Fig. 1) due to its reduced switch and capacitor voltage stress as compared with other switchedcapacitor (SC) topologies [12]. This paper presents three primary contributions.…”

“…This paper presents three primary contributions. First, a comparison of two recently published switching schemes, N-phase switching [12] and Split-phase switching [13], is presented and demonstrates the advantages of each. It is found that for the same hardware the N-phase scheme is more lightload efficient, whereas the Split-phase scheme excels at heavy loads.…”

Reducing COSS Switching Loss in a GaN-based Resonant Cockcroft-Walton Converter Using Resonant Charge Redistribution

“…Within the past several years there has been increasing interest in hybridized switched-capacitor power converters with record breaking power densities having been demonstrated [1,2]. Recent work ( [1][2][3][4][5][6][7]) has focused on developing topologies and switching regimes that eliminate the transient inrush currents associated with fly capacitor voltage mismatch, described analytically as the slow-switching-limit (SSL) in [8]. Here a topology is adopted that also eliminates transient inrush currents but in addition attempts to achieve complete softswitching of all active devices by addressing the 𝐶 𝑂𝑆𝑆 -related dynamic switching loss inherent in all of the aforementioned designs.…”