The effect of switching frequency, duty ratio, and dead times on a synchronous boost rectifier for low power electromagnetic energy Harvesters

Electromagnetic vibrational energy harvesters require rectification and boosting of their ac output voltage. This paper presents a single-stage, full-wave, synchronous boost rectifier circuit in an H-bridge configuration, and explores the dependence of both conversion efficiency and harvester utilisation on the precise switching patterns of the two `active diodes' and two `switching devices'. Switching instants are controlled via the following parameters: switching frequency, duty ratio, and dead times. Experimental results are presented that quantify the dependence of the output power and converter efficiency on these control parameters. Conversion efficiency up to 92% is achieved at 700 μW levels with externally powered gate drive circuit. The full-wave boost rectifier is capable of extracting up to 95% of the maximum available power from the harvester, when the switching parameters are set to provide optimised resistive apparent input impedance.