Does Charge Balancing Ensure the Safety of the Electrical Stimulation and Is It Power Efficient?

Safety issues are the most important concern in electrical stimulation. Equating the charge in the anodic and cathodic phases, namely charge balancing or charge equalizing, is a well-known method to avoid tissue damage and/or electrode corrosion. The electrode-tissue interface is not ideal in practice and with a charge-balanced waveform, the electrode voltage becomes more positive compared to the pre-pulse value and corrosion happens. In this paper, we show that a charge balancer ensures the safety of stimulation if the rate of the irreversible Faradaic reactions is negligible, or when the pulse width of the stimulation phases is not comparable to the time constant of the electrode-tissue interface. Furthermore, charge balancing is studied with mathematical modeling for different types of tissue models, and the results are used to show the conditions that charge balancing does not ensure the safety of the electrical stimulation, and employing charge balancing not only increases the power consumption of the electrical-stimulation systems but also increases the rate of the electrode corrosion in these conditions. The main goal of this paper is to show that a charge controller is a general solution for ensuring the safety of the electrical stimulation, with an efficient, not excessive, amount of charge for the reversal phase and should be employed instead of charge balancers in generic stimulators.