Since the current trend of solid state lighting (SSL) lies on modularization and integration, distributed drivers are gaining more popularity due to their flexibility, area-efficiency and low cost. A switched capacitor converter (SCC) which transfers energy only utilizing capacitors, rules out the use of inductive components, making such a converter the favoured topology as distributed drivers.
One aspect to implement distributed drivers is “driver on board”, where the drivers and light source are combined together on one carrier board. The power supply of such boards varies from regulated standard voltage to an unregulated wide range voltage, which presents difficulties for drivers to maintain high performance. For instance, to be compatible with the Power over Ethernet (PoE) standard which formulates 44V-57V as the voltage range, those drivers necessitate good line regulation, thereby, can obtain high efficiency.
Consequently, as mentioned before, one key challenge of switched capacitor converter is to achieve precise output voltage under wide range of power supply, that is, good line regulation.
For a conventional switched capacitor converter, the relationship between input and output voltage can be formulated as:VO=M*VIN−RO*IL 
Where, VO, VIN, RO, IL, M are input and output voltage, equivalent output resistance, load current and conversion ratio, respectively.
For a switched capacitor DC-DC converter whose topology is fixed, voltage is converted by only one conversion ratio. At one certain conversion ratio, output voltage is proportional to the input voltage. A switched capacitor converter having only one conversion ratio has limited line regulation performance, resulting in not only low efficiency, but large output power variation. This un-regulated output voltage is unacceptable when the voltage precision is strictly demanded.
One conventional approach to get a regulated output voltage out of a switch capacitor converter is to add a feedback loop to adjust the equivalent output resistance of the circuit.
Another conventional approach is cascading multiple SCC together, operating as a multi-stage successive-approximation (SAR) converter. Each stage divides the prior voltage into two down-scaled voltage ranges. Accordingly, if two stages are cascaded, four configurable ratios are available. Thus, N stages provide 2N possible ratios. Therefore, after cascaded multi-stage SAR SCC, high voltage resolution can be achieved.
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