A portable electrical stimulation system (102, 202) configured to percutaneously block nerve conduction, the system comprising: a modular power source; a switching circuit (302, 304) coupled to said modular power source and configured to continuously generate at an output of said switching circuit an electrical stimulation output at a plurality of selectable output level that spans over a range of output levels that can block nerve conduction; and a controller (122, 502) coupled to the switching circuit, the switching circuit having one or a programmable output level, wherein the output of the switching circuit is coupled to one or more electrodes (113, 115, 115a, 115b), directly or through a cable (108a, 108b), located at, or in proximity to, the target site, wherein the one or more electrodes placed in parallel, or substantially in parallel to a long axis of a peripheral nerve over an overlapping nerve region of greater than about 3 millimeters, characterised in that the switching circuit comprises either (i) a switching stage and a filter stage, the switching stage being configured to generate a square-wave amplitude modulated output, the filter stage being configured to shape the square wave amplitude modulated output to a sinusoidal waveform, or (ii) a switching stage and a filter stage, the switching stage being configured to generate a pulse-shaped amplitude modulated output, the filter stage being configured to shape the pulse-shaped amplitude modulated output to a non-sinusoidal waveform to continuously generate the electrical stimulation output at an output efficiency greater than 70%, preferably at an output efficiency greater than 90%. a modular power source; a switching circuit (302, 304) coupled to said modular power source and configured to continuously generate at an output of said switching circuit an electrical stimulation output at a plurality of selectable output level that spans over a range of output levels that can block nerve conduction; and a controller (122, 502) coupled to the switching circuit, the switching circuit having one or a programmable output level, wherein the output of the switching circuit is coupled to one or more electrodes (113, 115, 115a, 115b), directly or through a cable (108a, 108b), located at, or in proximity to, the target site, wherein the one or more electrodes placed in parallel, or substantially in parallel to a long axis of a peripheral nerve over an overlapping nerve region of greater than about 3 millimeters, characterised in that the switching circuit comprises either (i) a switching stage and a filter stage, the switching stage being configured to generate a square-wave amplitude modulated output, the filter stage being configured to shape the square wave amplitude modulated output to a sinusoidal waveform, or (ii) a switching stage and a filter stage, the switching stage being configured to generate a pulse-shaped amplitude modulated output, the filter stage being configured to shape the pulse-shaped amplitude modulated output to a non-sinusoidal waveform to continuously generate the electrical stimulation output at an output efficiency greater than 70%, preferably at an output efficiency greater than 90%.