Question

I cropped out Step 1 to only show information that may or may not be vital. I only need help with Step 2. Thank you.

10V Figure 1. BJT Bias Circuit Step 1. Consider the circuit of Figure 1. Assume that Q1 has VE 0.7V and /p-150 Neglect the Early effect; that is, assume V -oo. Use Vcc 10V Assume ICzI, but do not neglect the voltage drop across R due to base current. Voltage drop across RBB-007333V. Step 2. This step tests the sensitivity of Ic to variations in p Let VBB equal 1.27333V If the value of β were to increase by 50% (i.e., to 225), by what percentage would the collector current increase? Assume that E remains constant. (Hint: the voltage drop across RR changes.)

Answer 1

Apply the KVL to the input Loop -V_BB + I_b R_B + V_BE + I_E R_E = 0 thatis (1) step 1 Given R_L = 10k, R_BB = 22k, R_E = 1k, V_CC = 10V V_RBB = 0.07333V I_B = V_RBB /R_B = 0.07333/22k ohm I_B = 3.33 times 10^-6 A we know that beta = I_C /I_B I_C = beta I_B = 150 times 3.33 times 10^-6 I_C approximatelyequalto 0.5mA step 2: if beta = 225 V_BB = 1.2733 from equation (1) implies V_BB = I_b R_b + V_BE + I_E R_E I_B = V_BB - V_BE /R_B + (beta + 1)R_E [because I_E = (beta + 1)I_B] I_B = 1.2733 - 0.7/22k + (225 + 1)1k I_B = 2.31 times 10^-6 I_C = beta I_B = 225 times 2.31 times 10^-6 I_C_2 = 0.52 times 10^-3 Percentage of collector current increase = 0.52 times 10^-3 - 0.5 times 10^-3 /0.5 times 10^-3 times 100 = 2 times 10^-5 /0.5 times 10^-3