Input Circuit for Industrial Control with Low Heat Dissipation

An I/O circuit for use with an industrial controller provides an input circuit with low power dissipation through the use of a series connected substantially nonresistance impedance. An AC waveform input activates a light emitting diode (LED) bridge to provide an optical signal which illuminates a photosensitive solid-state switch thereby providing optical isolation between the industrial controller and the controlled process or machine. By using a series connected substantially nonresistance impedance, reduced current demand by the input circuit may be realized, which allows reduced power dissipation. As a result, the same circuit allows receiving input signals over a greater range, such as 120 volts AC and 240 volts AC, and allows significantly smaller components with closer spacing for a more compact design.