Merged Flyback–SC-Based Output Stage for Versatile Portable Transcutaneous Electrical Stimulators

This paper introduces a highly flexible multichannel output stage for battery-powered portable electric stimulators (ESs), based on novel power converter architecture. Compared with other solutions, the presented output stage for transcutaneous (surface) stimulations increases the number of applicable therapies, improves the battery operating time through reduced power consumption, and potentially results in more comfortable and shorter healing therapies. The new hybrid switch-mode power converter is a combination of flyback and switched-capacitor (SC) topologies. The flyback steps up the battery voltage and provides galvanic isolation. The following power-efficient SC stage replaces lossy linear current sources (CSs) of conventional solutions and produces pulses with a much higher slew rate, reducing the pulse energy needed to cause the stimulus. The SC also inherently produces pulses with zero-net charge, eliminating bulky blocking capacitors and/or dedicated discharging circuits. The regulation of the amplitudes of the pulses is performed with a new digital voltage-programmed current mode controller, forcing the output of the SC stage to behave as a CS. The flexible digital controller allows for creation of various types of pulses and also features several levels of patient protection. An experimental prototype of the output stage has undergone proof of principle tests with able-bodied individuals. The results show that the new output stage produces pulses with a 1-mA/ns slew rate, about two orders of magnitude higher than the other known solutions. The trials show that the faster slew rate pulses generate the same muscle contraction with 34% lower amplitudes, reducing energy consumption by 55%, allowing longer battery life of portable ES applications.