CHAPTER 18 BJT-TRANSISTORS.

งานนำเสนอเรื่อง: "CHAPTER 18 BJT-TRANSISTORS."— ใบสำเนางานนำเสนอ:

1 CHAPTER 18 BJT-TRANSISTORS

2 Function of Transistors

3 Main Applications of Transistors

4 BIPOLAR JUNCTION TRANSISTORS (BJTs)
BJT is constructed with three doped semiconductor regions separated by two pn junction There are three regions : Emitter Base Collector There are two type of BJT: npn pnp

5 Basic construction of BJT

6 การป้อนไฟให้กับ Transistor แบบ BJT
AC bias ป้อนสัญญาณไฟกระแสสลับ DC bias ป้อนสัญญาณไฟกระแสตรง กระตุ้นให้ BJT อยู่ในช่วงทำงานได้ แม้สัญญาณ input AC จะอยู่ในช่วง ติดลบ ขา BE: Forward bias ขา BC: Reverse bias Q-point อยู่ในช่วงใช้งาน Active Region

7 Transistor DC Biasing The BE junction is forward-biased
The BC junction is reverse-biased (Vbase ( B ) > Vemitter ( E) ) (Vbase ( B ) < Vemitter ( E) ) (Vcollector ( C ) > Vbase ( B ) ) (Vcollector ( C ) < Vbase ( B ) )

8 Transistor Operation

9 DC current gain Alpha and Bata
The Collector current is equal to times the emitter current The collector current is equal to the base current multiplied by has a value between 0.950 and 0.995 has a value between 20 and 200

10 Transistor Voltages (DC bias)
2 Voltage Sources

11 Transistor Voltages (DC bias)
Voltage divider Sources Use only a single dc source to provide forward-reverse bias to the transistor Resistor R1 and R2 form a voltage divider that provides the base bias voltage

12 Transistor Voltages (DC bias)
Voltage divider Sources

13 Input Resistance at the Base
Voltage divider Sources

14 Base Voltage V

15 THE BIPOLAR JUNCTION TRANSISTOR AS AN AMPLIFIER

16 THE BIPOLAR JUNCTION TRANSISTOR AS AN AMPLIFIER
When both junction are forward-biased, the transistor is in the saturation region of its operation When VCE exceeds 0.7 V, the base-collector junction becomes reverse-biased and the transistor goes into the active or linear region When IB=0 the transistor is in the cutoff region

17 Load Line Operation Load Line: VCE vs IC

18 Quiescent or Q-Point

19 Quiescent or Q-Point Load Line AC Sources DC Sources IB = 400 uA

20 Signal Operation on the Load Line
Q-point ต่ำเกินไป จ่าย IB น้อยเกินไป Q-point สูงเกินไป จ่ายไปให้ IB มากเกินไป Q-point เหมาะสม ค่ากำลังขยาย beta มากเกินไป

21 BJT Transistor AC Amplifier
Class A วงจรทำงานตลอดเวลา full cycle of AC input signal (360o) Class B วงจรทำงาน half cycle หยุด half cycle (180o) Class C วงจรทำงานน้อยกว่า half cycle (< 180o)

22 BJT Transistor AC Amplifier: Class A
ขยายสัญญาณได้ 3 แบบ Common Base Amplifier (CB): Voltage Amp. Common Emitter Amplifier (CE): Power Amp. Common Collector Amplifier (CC): Current Amp.

23 การวิเคราะห์การขยายสัญญาณ AC (i/p)
ใช้ Equivalent Circuit มาเป็นตัวแทน BJT (AC model) Simple model Hybrid Π model h parameter model

24 Simple Model (small signal analysis)
BJT ( npn type) Simple model C E C E B B

25 Simple Model ถ้าโจทย์ไม่ให้ = Dynamic AC resistance ที่ขา E-B
Parameter in BJT equivalent circuit ถ้าโจทย์ไม่ให้ = Dynamic AC resistance ที่ขา E-B = Dynamic AC resistance ที่ขา C-B = ค่าสูงมากระดับ MΩ ถ้าโจทย์ไม่ให้

26 Amplifier Gain Calculation Process
Calculating DC bias DC current and voltage in DC bias circuit Checking load line and Q-point Calculating AC amplifier gain re’ from IE(DC) Voltage gain (AV) = Current gain (Ai) = Power gain (AP) = AV Ai

27 Common Base Amplifier ( CB Amp )
BJT B vin vOUT E C B Simple model for AC small signal analysis

28 CB Amp. Circuit Vcc

29 Common Base Amplifier ( CB Amp )

30 Common Emitter Amplifier ( CE Amp )
B C BJT E vin vOUT B C E Simple model for AC small signal analysis

31 CE Amp. Circuit without CE
Vcc R1 R2

32 Common Emitter Amplifier ( CE Amp: no CE )

33 Common Emitter Amplifier ( CE Amp: no CE )

34 CE Amp. Circuit with CE Vcc

35 Common Emitter Amplifier ( CE Amp: with CE from E-GND )
Higher voltage gain

36 Common Emitter Amplifier ( CE Amp: with CE from E-GND )

37 Common Collector Amplifier ( CC Amp )
Common Emitter Amplifier B E BJT C vin vOUT B E C Simple model for AC small signal analysis

38 CC Amp. Circuit Vcc

39 Common Collecter Amplifier ( CC Amp)

40 Common Emitter Amplifier (CC Amp)

41 THE BJT AS A SWITCH Conditions in cutoff Conditions in saturation

42 BJT PARAMETERS AND RATINGS
IF the temperature goes up, goes up, and vice versa.

43 BJT PARAMETERS AND RATINGS
Maximum Transistor Ratings PD(max) = maximum power dissipation