PURPOSE: To protect the load by providing 2nd level control circuit with an equal characteristic to that of 1st level control circuit and a voltage addition amplifier between a preamplifier and a power amplifier, and supplying the output of the power amplifier and the additional amplifier to both terminals of the load.
CONSTITUTION: The 1st level control circuit consists of a 1st variable impedance circuit 2, a control circuit 11 and a variable resistor 12 and the 2nd level control circuit consists of a 2nd variable impedance circuit 6, the control circuit 11 and the variable resistor 12. An AC input signal is amplified by a preamplifier and fed to a load. In this case, an output DC voltage of the 1st level control circuit is amplified by the power amplifier and fed to one terminal of the load and the output DC voltage of the 2nd level control circuit with the equal gain as that of the 1st level control circuit is amplified by the additional amplifier with an equal gain as that of the power amplifier and supplied to the other terminal of the load. Thus, the voltage across the load is equal and the amplifier not giving a DC current to the load is obtained and the load is protected.
KOKUBO KENICHI
KOJIMA HIROSHI
