An I/O circuit for use with an industrial controller provides a photovoltaic optical isolator communicating between a controller and a field-side of the I/O circuit, the photovoltaic optical isolator eliminating the need for high wattage power dropping circuits for powering the field-side of the I/O circuit from high-voltage field signals. The field effect transistor type transistors permit use of the low-power photovoltaic optical isolator while allowing flexible connections to various field circuit types.