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Model 10811A/B
48
Figure 8-11. Turn-on Current Limit Circuit
8-39. HEATER TRANSISTOR BALANCE
8-40. Because heater transistors Q7 and Q8 are not equally spaced from the crystal, it is necessary to
offset the power dissipation between the two transistors.
shows a simplified
schematic of this circuit. Amplifier U1A references a voltage divider across Vcc (R25, R26) and a
divider referenced to the mid-point between the heater transistors. From this U1A controls the
base current of Q7 to insure the Voltage at the mid-point between the heater transistors is a
constant percentage of Vcc (V4
≈
0.57 Vcc ± 2%).
Figure 8-12. Heater Transistor Balance Circuit.
Содержание 10811A
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