On the Effect of Parasitic Capacitances on the Voltage Sharing of Series-Connected Diodes

Series-connected diodes have numerous applications in high-voltage converters and pulsed power supplies. Providing balanced voltage sharing for the diodes in the series structure is mandatory to avoid diodes break down and cascading failure due to the unbearable overvoltage conditions. One of the important factors affecting the voltage sharing of the diodes is the parasitic capacitance that exists between the diodes and the ground. The frequent charging and discharging of these capacitors after each operation of the diodes injects an extra electrical charge into the diodes junction capacitors. This leads to an unbalanced voltage sharing for the diodes in the off-state since the mentioned electrical charges are not equal. This paper first determines the parasitic capacitors using finite element simulations (COMSOL software) and subsequently calculates the unbalanced voltage sharing of the diodes due to these capacitors. Finally, a proposition is provided to mitigate the negative effect of the parasitic capacitors on the voltage sharing of the series-connected diodes. The PSPICE simulations verified the achievements of the paper.