Electrolytic Double Layer Capacitors (EDLCs), colloquially known as supercapacitors, are an emerging solution for energy storage competing with batteries. With capacities ranging from 0.5 F to a few kF (!), they are capable of charging up quickly, and can deliver very high peak power when discharging. Unfortunately, EDLCs have a rather low maximum voltage of 2.7V typically, which is borderline for electronics but insufficient to drive loads such as motors, LED strips, solenoids, and so on. Multiple EDLCs can be connected in series to increase the maximum voltage, but this also increases the ESR, and the application will still be affected by the dropping supply voltage as the capacitors dicharge.
To solve these issues, a boost converter is an ideal solution to step up the low EDLC voltage to a constant DC output. To supply 2 amps of output current at 12V, the current drawn from the ELDC gets rather large as it nears depeletion. This design uses a custom transformer built by Chinese company Ranlo, with a resonant frequency of 30 kHz, primary current rating of 25A (!) and step-up ratio of 1:10. The output uses active rectification using an N-MOSFET bridge, and an LC filter to suppress the 30 kHz ripple from the output rail.
Topologically, the primary of the transformer is driven by a H-bridge built with 2 integrated half bridges. A current transformer on the input provides feedback necessary for switching control. The control loop is implemented in software on an AVR A2560 microcontroller. A LED bar is included for visual feedback of the remaining charge.