written 3.5 years ago by |
Performing DC analysis by open circuiting all capacitors
The voltage across resistor R2 can be given by the expression
The current through R1 is
$I_1=\dfrac{V_{CC}-V_B}{R_1}$
Similarly, current through R2 is
$I_2=\dfrac{V_B-V_{EE}}{R_2}$
Since there is no path for these currents to take another loop, these currents have got to be the same which brings us to the foll. equation
$\dfrac{V_{CC}-V_B}{R_1}=\dfrac{V_B-V_{EE}}{R_2}$
$\dfrac{V_{CC}-V_B}{R_1}-\dfrac{V_B-V_{EE}}{R_2}=0$
$\dfrac{V_{CC}R_2-V_BR_2-V_BR_1+V_{EE}R_1}{R_1R_2}=0$
${V_{CC}R_2-V_BR_2-V_BR_1+V_{EE}R_1}=0$
$V_{CC}R_2+V_{EE}R_1=V_B(R_1+R_2)$
$\therefore V_B=\dfrac{V_{CC}R_2+V_{EE}R_1}{R_1+R_2}$
NOTE: Using the above equation, we can easily get VB but just in case you want a easier equation, we will simplify the obtained equation
$V_B=\dfrac{V_{CC}R_2+V_{EE}R_2-V_{EE}R_2+V_{EE}R_1}{R_1+R_2}$
$V_B=\dfrac{V_{EE}(R_1+R_2)}{R_1+R_2}+\dfrac{R_2(V_{CC}-V_{EE})}{R_1+R_2}$
$\therefore V_B=V_{EE}+(V_{CC}-V_{EE})\times\dfrac{R_2}{R_1+R_2}$
$\therefore V_B=-5+\big(5-(-5)\big)\times\dfrac{2\times10^3}{12\times10^3+2\times10^3}$
$\therefore V_B=-3.571\ V$
$R_B=R_1||R_2$
$R_B=\dfrac{12\times10^3\times2\times10^3}{12\times10^3+2\times10^3}$
$\therefore R_B=1.714\ K \Omega$
Applying KVL to Base - Emitter Loop
$V_{B}-I_BR_B-V_{BE}-I_ER_E+V_{EE}=0$
But, $I_E=(1+\beta)I_B$
$V_B-I_BR_B-V_{BE}-(1+\beta)I_BR_E+V_{EE}=0$
$V_B-V_{BE}+V_{EE}=I_B\big[R_B+(1+\beta)R_E\big]$
$I_B=\dfrac{V_B-V_{BE}+V_{EE}}{R_B+(1+\beta)R_E}$
$I_B=\dfrac{-3.571-0.7+6}{1.71\times10^3+(1+100)500}$
$I_B=33.135\ \mu A$
We know that, $I_C=\beta I_B$
$I_C=100\times34.237\times10^{-6}$
$\therefore \underline{\underline{I_C=3.135\ mA}}$
Applying KVL to the Collector - Emitter Loop
$V_{CC}-I_CR_C-V_{CE}-I_ER_E+V_{EE}=0$
But $I_C\approx I_E$
$\therefore V_{CC}-I_C\big[R_C+R_E\big]-V_{CE}+V_{EE}=0$
$V_{CE}=V_{CC}-I_C\big[R_C+R_E\big]+V_{EE}$
$\therefore V_{CE}=5-3.135\times10^{-3}\big[5\times10^3+500\big]+5$
$\therefore \underline{\underline{V_{CE}=-8.288\ V}}$