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Design a Single stage RC coupled amplifier using FET BFW-11 biased to provide 3.5mA to achieve voltage gain of 10, lower cut of frequency of 20 Hz and to provide Vo=2.5V.
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written 3.5 years ago by |
- We know the gain of a BJT transistor given y the formula
$A_v=\dfrac{V_o}{V_i}$
Hence the Output Voltage is the product of Gain and Input Voltage
$V_{o}=300V$
We know the Stability factor for a BJT transistor is given as
$S=\dfrac{(\beta+1){(1+\dfrac{R_1}{R_L})}}{({\beta+1)}+\dfrac{R_1}{R_L}}$
- From data sheet of BJT147B transistor we have Gain value of 150 to 460
- We can take gain value as 150 here
$10=\dfrac{(151){(1+\dfrac{R_1}{10000})}}{({151)}+\dfrac{R_1}{10000}}=\dfrac{(151){(1+{0.0001R_1}{})}}{({151)}+{0.0001R_1}{}}$
$=1510+0.0001R_1=151+0.0151R_1$
$=0.015R_1=1359$
$R_1=90.6K\Omega$
- Let$V_{cc}=10V;V_{CE}=4V;I_C=10mA$
- The Collector current is product of Current gain and Base current
$I_b=\dfrac{I_{c}}{{\beta}}$
$I_b=\dfrac{{2\times 10^{-3}}}{{150}}=0.01mA$
- We know that by applying in Collector Emitter junction we have
$V_{CE}=V_{CC}-I_C(R_C+R_L)$
$4=10-2(R_c+1000)=-2R_c+2010$
$-2R_c=-2006$
$R_C=2.006K\Omega$
- By ohms law the Base voltage is given by
$V_B=I_C\times R_L=2V$
- By voltage division we have the base voltage as
$V_B=\dfrac{R_{2}V_{cc}}{R_1+R_2}$
$2=\dfrac{10R_2}{90600+R_2}$
$8R_2=181200$
$R_2=22.650K\Omega$
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