A portable switching bi-phasic stimulator with level-shifting inverter for functional electrical stimulation operating under a 6V supply voltage

This paper presents a compact architecture of portable functional electrical stimulator (FES) together with a level-shifting digital inverter. The presented architecture is composed of boost converter block with compact limiter circuit. The bi-phasic pulse generation is made from H-bridge switches with the boosted voltage from the boost converter block. The H-bridge switches are controlled by a level-shifting inverter which is composed of only four MOSFET devices with two capacitors. The clocking scheme for minimize power consumption is also a key point for reducing average power consumption in this work. The simulation results from LTSpice IV show that the presented stimulator can generate stimulating bi-phasic pulses with approximately +/-21V amplitude in voltage and constantly supply +/-19.2mA current to the load. The simulated bi-phasic pulse has pulse width of 326μs with frequency of 28.6Hz. The presented system can be operated under a single 6V supply voltage and the average power consumption is 117mW at stimulating frequency of 28.6Hz which can continuously operate under two CR2032 batteries for more than 11 hours. With this level of power consumption, the presented work is very suitable for using as a portable stimulator.