METHOD FOR OVERLOAD PROTECTION OF OPERATIONAL AMPLIFIER INPUT Russian patent published in 2013 - IPC H03F1/54 

FIELD: electricity.

SUBSTANCE: input current is limited using a cathode follower on a vacuum triode with high internal resistance, and limitation of input voltage is achieved by feeding a signal to the input of the operational amplifier from a resistor connected in the cathode circuit of the cathode follower. High internal resistance of the vacuum receiving amplifier tube provides an effective barrier for penetration of large currents and high voltages at the input of electronic equipment. Connecting the receiving amplifier tube at the input of the operational amplifier on a cathode follower circuit operating in current amplification mode increases load capacity of signal transmission lines. High linearity of the cathode follower provides the technical result - quality of signal transmission. Limitation of input voltage of the signal is achieved by applying voltage at the input of the operational amplifier from a resistor connected in the cathode circuit of the cathode follower. If pulse voltages exceeding electrical strength parameters of the vacuum tube penetrate into the communication line, the former undergoes electromechanical breakdown, which also prevents penetration of high-voltage pulses at the input of the electronic equipment.

EFFECT: effective barrier for penetration of large currents and high voltages at the input of electronic equipment, thereby increasing reliability of operation thereof.