Static bias circuit diagram of triode common emitter amplifier

The emitter quiescent potential and bias voltage forming circuit (i.e. voltage follower) of the common emitter amplifiers V502, V504 and V506 are shown in Figure 3. The active filter composed of V507, VD502, VD503, R534, R535, C514, and R540 is the emitter static bias voltage follower circuit of V502, V504, and V506. R535 and R534 form a voltage dividing network. The voltage dividing point of 1.85V is stepped down by VD503 in series with VD502 to the base of V507, which is about 0.7V. Its emitter voltage is about 1.35V. As common emitter amplifiers V502, V504 and V506 Only the emitter bias voltage source of the amplifier tube. The base bias voltage of the common-base amplifier is directly provided by the +9V power supply. The base of the common-base amplifier tube is AC grounded through C513. Therefore, V501, V503, and V505 are common-base circuits in terms of input and output signals. V507 (PNP type tube) is used as the emitter static bias voltage follower of the common-emitter amplifier tube because the bases of the common-base amplifier tubes V501, V503, and V505 are all connected to the +9V power terminal. A slight change in the power supply voltage will affect its static operating point, causing the static collector potential of the output tube to change and affecting the brightness of the screen. To this end, the circuit in the figure is used to make the emitter bias voltage of the common emitter amplifier change synchronously with the slight change of the +9V power supply. That is, when the +9V power supply changes slightly, the emitter voltages of V502, V504, and V506 follow the changes to ensure that the common emitter amplifier emitter bias voltage changes synchronously with the slight change of the +9V power supply. The emitter and common-base transistors do not change with slight changes in the power supply, which means that the static potential of the collectors of V501, V503, and V505 does not change. On the one hand, this can ensure the consistency of the performance of large batches of products, and also ensure that the brightness of a single machine is not affected by slight changes in the power supply voltage. The junction voltage of VD503 and VD502 (0.5-0.7V) decreases as the temperature rises, causing the emitter potential of V507 to rise, which can compensate for the increase in static voltage of the two Shenlian transistors of the common-emitter and common-base cascade amplifiers as the temperature rises. The influence of the change in the operating point reduces the temperature drift of the final amplifier and greatly improves the working stability. Since C514 is connected between the power supply +9V and the base of V507, it can also avoid brightness transients caused by power supply transients.