A simple constant-current neural stimulator with accurate pulse-amplitude control

A simple constant-current electrocutaneous stimulator for high-impedance loads using low-cost, standard high-voltage components is presented. A voltage-regulator powers an oscillator built across the primary of a transformer whose secondary delivers, after rectification, the high-voltage supply to switched current-mirrors in the driving stage. Since the compliance high-voltage is proportional to the stimulation current, overall power consumption is minimized. By adjusting the regulated voltage, control of the pulsed-current amplitude is achieved. A prototype with readily available components features stimulation currents of amplitude and pulsewidth in the range 0≤1_skin≤20 mA and 50 μs≤T_pulse≤1 ms, respectively. Pulse-repetition spans from 1Hz to 10 Hz. Worst-case ripple is 3.7% @I_skin=1 mA. Measured pulse fall-time is shorter than 32 μs. Overall consumption is 4.4 W @I_skin=20 mA. Subject isolation from power line is 4 kV.