| 摘要 |
PURPOSE:To prevent a final stage power transistor (TR) from being damaged at the start of a transmitter, by detecting an output of the final state output TR and limiting the over excitation of the final stage TR with an output difference between a detected voltage and a reference voltage. CONSTITUTION:An advancing wave output of the final stage output TR6 of an automatic control transmitter is detected at a pickup 13 and a voltage V0 detected at a diode D1 is inputted to an automatic high frequency power control APC comparison circuit 11. The V0 is compared with a reference voltage V1 adjusting a constant voltage EIN with a variable resistor R1 at the circuit 11 and the difference voltage controls an output limit circuit 12. Since no detected output due to the D1 exists just after the start of transmission, although the difference voltage of the circuit 11 is high and a TRQ2 of the circuit 12 is conductive at the saturated current, an output voltage E0 of the TRQ1 is decreased to a value smaller than the voltage EIN with the base voltage of a TRQ3, the over exitation of an amplifier 5 at the exciting stage is limited, the damage of the TR6 is prevented and the output set value at normal operation is controlled. |
