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Universal Input Isolation Circuit Disclosure Number: IPCOM000043640D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05

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Smoley, D Sponsler, MJ [+details]


The circuit illustrated uses field-effect diodes (also known as current zener diodes) to enable a wide range of input voltages to activate a phototransistor. These diodes (D5 - D6) will conduct only 3 mA of current. The effective resistance of the diodes increases with an increase of applied voltage. With the diodes acting as self-adjusting variable resistors, the circuit will function with an input of 5 V to 120 V, AC or DC. This circuit allows great flexibility since it permits the phototransistor to be connected to various machines or computers.