Series-Connected Substrate-Integrated Lead-Carbon Hybrid Ultracapacitors with Voltage-Management Circuit

Cell voltage for a fully-charged substrate-integrated lead-carbon hybrid ultracapacitor is about 2.3 V. Therefore, for applications requiring higher dc voltage, several of these ultracapacitors need to be connected in series. However, voltage distribution across each series-connected ultracapacitor tends to be uneven due to tolerance in capacitance and parasitic parallel-resistance values. Accordingly, voltage-management circuit is required to protect constituent ultracapacitors from exceeding their rated voltage. A design of the 12 V substrate-integrated lead-carbon hybrid ultracapacitor by series-connected six 2 V cells with co-located terminals is presented in Figure 1 (a). The schematic diagram of voltage-management cell-balancing circuit for the ultracapacitor is shown in Figure 1 (b). The ultracapacitor with the voltage-management circuit is tested, and the data are summarized in Figure 2. It is clearly seen that in steady state, the voltage tends to distribute uniformly across the individual ultracapacitor in the series arrangement.