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