The Output Circuit of a Biphasic Constant Current Electrical Stimulator

Abstract

Abstract-An Electrical Stimulator (ES) can promote physiological benefits during rehabilitation of patients with spinal cord injury. One of the main circuits in an ES system is its output stage. This paper outlines a transformer-based output circuit topology and shows the results obtained during the development of the ES biphasic output. The current in the circuit is controlled by a voltage-to-current converter whose input is driven by amplitude modulated pulses generated by a microcontroller. Darlington configuration transistor switching is responsible for regulating the current flow in the transformer's primary coil. The pulse width, frequency and amplitude can be set accordingly. Battery-supplied power enhances patient safety by avoiding use of high voltage sources. Tests with the transformer-based prototype indicated efficiency on pulse generation, transfer of data packets between stages, and amplification of signals. The circuit provided output currents of 200 mA and a 200 V on a 1 kΩ load. The pulse frequency varied from 500 to 5000 Hz, and pulse width from 30μs to 400μs. The burst frequency ranged from 10 to 100 Hz. The designed system represents a useful and versatile tool for functional and therapeutic applications since it has resources for patient safety and can be altered and expanded.

A Flexible Pulse Generator Based on a Field Programmable Gate Array Architecture for Functional Electrical Stimulation

“…Moreover, a simple PWM module inside the FPGA is implemented to control the pulse amplitude for each stimulation channel (combined with the DAC with PWM inputs and the "signal mixer" blocks). In contrast, most electrical stimulation designs (either based on microcontrollers or FPGAs) use serially controlled (SPI or I2C) DACs to build the pulse shape, width, and amplitude, completely within the DAC (Nogueira et al, 2017). However, it is simpler and more efficient to implement one PWM module inside the FPGA for each stimulation channel, than to implement an SPI communication module for handling as many DACs as stimulation channels.…”

Precision Phosphene Control Through Cutaneous Facial Electrical Stimulation

“…The act of paralleling multiple waveform generators together is a method of supplying multiple electrodes at the same time. One method of paralleling is through common-grounding [53], [56] the waveform generators and the other way is through galvanically isolating them [67]. The act of isolation is usually done through magnetic power isolation, using a transformer [59].…”

Precision Phosphene Control Through Cutaneous Facial Electrical Stimulation

“…The act of paralleling multiple waveform generators together is a method of supplying multiple electrodes at the same time. One method of paralleling is through common-grounding [53], [56] the waveform generators and the other way is through galvanically isolating them [67]. The act of isolation is usually done through magnetic power isolation, using a transformer [59].…”