| 摘要 |
PURPOSE:To prevent the reduction of the input impedance for the noninverse input terminal by inserting the 1st and 2nd diodes which are connected in opposite polarity to each other between the noninverse terminal and the output terminal of the operational amplifier, and thus to secure protection to the overinput with a simple circuit. CONSTITUTION:The signals supplied from signal input terminal 5 are supplied to the noninverse input terminal of operational amplifier 4 via input resistance 1, and the output of amplifier 4 is applied to the inverse input terminal of amplifier 4 as well as to output terminal 6. Then 1st and 2nd diodes 2 and 3 connected to each other in the opposite polarity are inserted between the noninverse input terminal and terminal 6 of amplifier 4, and the overlap voltage is made identical between diodes 2 and 3. Thus the voltage application is avoided to diode 3, and the signal applied to input terminal 5 is delivered to terminal 6 with no effect of diodes 2 and 3. In case the overinput is applied, the voltage of the noninverse input terminal of amplifier 4 is set lower than the voltage obtained by applying the forward voltage of diodes 2 and 3 to the saturation voltage to secure the protection to the overinput. |
