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28V Input to 0V to 28V Output SEPIC SuperCap Charger with Input Current Limit

28V Input to 0V to 28V Output SEPIC SuperCap Charger with Input Current Limit

In this circuit, a supercapacitor is charged from it's fully uncharged state up to a full charge voltage of 28V. This wide output voltage range is accomplished using a SEPIC topology. The built in input current limit of the LT3956 simplifies the design. The LT3956 is a DC/DC converter designed to operate as a constant-current source and constant-voltage regulator. It is ideally suited for driving high current LEDs. It features an internal low side N-channel power MOSFET rated for 84V at 3.3A and driven from an internal regulated 7.15V supply. The fixed frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages. A ground referenced voltage FB pin serves as the input for several LED protection features, and also makes it possible for the converter to operate as a constant-voltage source. A frequency adjust pin allows the user to program the frequency from 100kHz to 1MHz to optimize efficiency, performance or external component size.