Positive SSL
BLOCK
BLOCK
1 如圖所示，若RB = 400kΩ、RC = 1kΩ、RE = 1kΩ、VCC=10.7V、β=100 求 Ri?
A 400kΩ
B 200kΩ
C 100kΩ
D 1.25kΩ
  

先算 `r_π`

`400k*I_B+0.7+1k*I_E` = 10.7

`400k*I_B+100k*I_B` = 10

`500k*I_B` = 10

`I_B` = `10/(500k)`

`I_B` = 0.02 mA

`r_π` = `(25m)/(0.02m)`

=1250Ω

化成交流等效電路，如下圖

`R_i` = 400k//`r_π`

= 400k//1.25k ≒ 1.25kΩ