A high efficient adiabatic Transcutaneous Electrical Nerve Stimulator (TENS) with current regulation

Abstract

Transcutaneous Electrical Nerve Stimulators (TENS) are used to deliver electrical pulses to different parts of body with main application of rehabilitation and pain relief. This paper presents a highly efficient adiabatic stimulator which can be directly connected to a lithium-ion battery. With the adiabatic feature, the stimulator provides the minimum voltage that is needed for the load to keep the stimulation current constant. A mathematical representation is presented for analyzing the improvement of the efficiency of adiabatic stimulators vs conventional current mode stimulators. The system consists of a Flyback converter with an H-bridge in the output stage to deliver biphasic pulses. The output current is directly sensed and regulated by making use of a current controlled PWM controller. The small signal transfer function of the stimulator is extracted and a compensation network is designed and implemented based on the extracted transfer function. The overall system is simulated in MATLAB/SIMULINK to evaluate the performance of the proposed stimulator. A stimulator prototype is also implemented by making use of off-the-shelf components in a 4-layer Printed Circuit Board (PCB) with the dimension of 96 mm * 89 mm. It delivers up to 60 mA with maximum voltage of 80 V. The peak total efficiency of the stimulator is 71%.