OVERVOLTAGE PROTECTING CIRCUIT

摘要

PURPOSE:To decrease the number of control parts and to improve the reliability of an overvoltage protecting circuit by providing a variable resistance to an output circuit of a photocoupler to control the detection level of overvoltage and therefore simplifying the constitution of a detection level control circuit with continuous variation of the detection level. CONSTITUTION:A variable resitance RV is put between the emitter and the base of a photocoupler PI. If the value of the RV is set infinite, the input and output currents If and Ic have approximately rectilinear rises with the zero point defined as a start point. The rise point of the current Ic moves to the right side as the value of the RV is reduced from the infinite value, and the current Ic has a rise approximately in parallel to a characteristic curve that is obtained when the variable resistance value is set infinite. Therefore the conditions to obtain an output current at the coupler PI can be controlled by changing the value of the resistance RV.