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Recall Lecture 12 Voltage Transfer Characteristics Biasing of BJT

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Presentation on theme: "Recall Lecture 12 Voltage Transfer Characteristics Biasing of BJT"— Presentation transcript:

1 Recall Lecture 12 Voltage Transfer Characteristics Biasing of BJT
Vo versus Vi Biasing of BJT Three types of biasing Fixed Bias Biasing Circuit Biasing using Collector to Base Feedback Resistor

2 Bipolar Transistor Biasing

3 Voltage Divider Biasing Circuit
This is a very stable bias circuit. The currents and voltages are almost independent of variations in .

4 Analysis Redrawing the input side of the network by changing it into Thevenin Equivalent RTH RTh: the voltage source is replaced by a short-circuit equivalent

5 Analysis VTH VTh: open-circuit Thevenin voltage is determined. VTH
Inserting the Thevenin equivalent circuit Use voltage divider

6 Analysis The Thevenin equivalent circuit

7 Example Find VCE ,IE, IC and IB given
β=100, VCC=10V, R1 = 56 k, R2 = 12.2 k, RC = 2 k and RE = 0.4 k VTH= R2 /(R1 + R2 )VCC VTH = 12.2k/(56k+12.2k).(10) VTH = 1.79V RTH = R1 // R2 = 10 k

8 BJT Biasing in Amplifier Circuits
VTH = RTH IB + VBE + RE IE 1.79 = 10k IB k ( +1)IB IB = µA IC = IB = 100(21.62)=2.16mA IE = IC + IB = 2.18mA VCC = RC IC + VCE + RE IE 10 = 2k(2.16m)+VCE +0.4(2.18m) VCE = 4.8 V

9 VCE(V) IE (mA) IC (mA) IB (mA)
VCE(V) IE (mA) IC (mA) IB (mA) Measured 0.16 V  5.441 mA  5.382 mA  0.059 mA

10 Example – A Design Question
VCC = 10 V IE = 1 mA =100 RE = k RTH = 33 k Determine the values of R1 and R2

11 R2 = 38.8 k BE Loop: IBRTH + 0.7 + IERE – VTH = 0
VTH = 1.5 V We know: 1.5 (220 + R2) = 10R2 330 = 8.5 R2 R2 = 38.8 k


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