A high voltage, constant current stimulator for electrocutaneous stimulation through small electrodes

A high-voltage stimulator has been designed to allow transcutaneous stimulation of tactile fibers of the fingertip. The stimulator´s output stage was based upon an improved Howland current pump topology, modified to allow high load impedances and small currents, The compliance voltage of approximately 800 V is achieved using commercially available high-voltage operational amplifiers. The output current accuracy is better than ±5% over the range of 1 to 25 mA for 30 μs or longer pulses. The rise time for square pulses is less than 1 μs. High-voltage, common-mode, latch-up power supply problems and solutions are discussed. The stimulator´s input stage is optically coupled to the controlling computer and complies with applicable safety standards for use in a hospital environment. The design presented here is for monophasic stimulation only, but could be modified for biphasic stimulation.