| 摘要 |
PURPOSE:To change output impedance simply and stably without using a load current detecting resistor having high wattage by dividing voltage drop due to the emitter resistance of push-pull output transistors (TR) and feeding back the divided voltages negatively. CONSTITUTION:Emitter resistors R6, R7 having about 0.1-1OMEGA are inserted between the emitters of output TRs Q1, Q2 in order to obtain thermal stability in an push-pull output stage executing B-type operation by a complementary TR. If the connection point 0 between the resistors R5 and R6 is selected as a point negatively fed back from the output stage, the output impedance is zero, and when the connection point 0' between voltage dividing resistors R3 and R4 connected to the emitter terminals of the output TRs Q1, Q2 is selected, the output impedance is the same value as the emitter resistors R5, R6. Therefore, the output impedance can be changed optionally from zero to the emitter resistance and the influence of a load resistor RL is completely prevented by connecting a variable resistor VR between the connection point 0 of the emitter resistors R5, R6 and the connection point 0' of the voltage dividing resistors R3, R4. |
