In a sign that switched capacitor architectures are gaining wider market acceptance for power conversion, Dialog Semiconductor has used the approach in a patent application for the DC-DC converter that can handle multiple battery cells.
When multiple cells are provided in series in a system such as a laptop, the voltage supplied by a fully charged battery will be higher than the voltage required for operation of the device and so a step down DC-DC conversion is required. A buck converter is usually used for this purpose, which uses an inductor as an energy storage element and has switching elements that selectively couple the inductor with an input voltage, in order to step down the voltage.
However, stepping down from a relatively higher voltage with a buck converter requires relatively high inductance or a relatively high switching frequency and so there are either large components or large losses within the buck converter. In general, stepping up or down a large voltage with a DC-DC converter involves large switching losses. The variable output voltage in such packs can be as high as 4.2V for a fully charged cell, dropping down to 2.5V at the end of a full discharge, creating a challenge for a DC-DC converter.
Dialog Semiconductor has patented a DC-DC converter design that can handle the variations from a pack with multiple cells. It uses a network of switched capacitors to store energy to handle the variation in the cells and even help balance the charge in each cell. This would make the conversion much more efficient.
Helix Semiconductors and Murata’s pSemi subsidiary have developed DC-DC converters using switched capacitor architectures.
In general, the multiple input inductive converter provided by the two sets of switching elements do not have to be combined as part of a single unit. Within a more general power tree multiple Power Management ICs and regulators may be connected to different intermediate nodes of a serial battery stack and a separate charge balancing converter may ensure that all serial cells are regulated to the same voltage.
As the capacitive converter can balance the charge of a serial stack independent from which cell has highest voltage, it could also be combined with for example a battery charger charging only a subset of the cells and the input charge is distributed by the capacitive converter to cells connected in series until all the cells have similar voltage.
The patent is US20200006973.
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