Bipolar Junction Transistor (BJT) | Introduction | Operation | Uses
- 1. BJT Introduction | Operation | Uses
- 2. Presented by Toukir Ahmed Chowdhury(1603096) Main Uddin Sagar (1603082) Protap Sarker (1603073) Subash Chandra Das(1603127) Towhedul Islam(1603080) DEPARTMENT OF MECHANICAL ENGINEERING CUET
- 3. Topics of discussion: • What is BJT? • History of its invention • Physical structure of BJT • BJT symbol • BJT operations • Application of BJT: 1) As a switch 2)As an amplifier • Other uses of BJT • BJT vs MOSFET
- 4. What is BJT? BJT stands for Bipolar Junction Transistor which is a type of transistor that uses both electrons and holes as charge carriers. • A 3-terminal device • Used in amplification of weak signals and switching operations • Plays a vital role in both Analog and Digital electronics Bipolar – Current flows due to both majority and minority charge carriers i.e. electrons and holes Junction – Presence of two p-n junctions connected back to back Transistor – Transfer + Resistor
- 5. History of its invention The first bipolar transistor was invented at Bell Labs by William Shockley, Walter Brattain, and John Bardeen in 1948. The inventors received the Nobel Prize in Physics in 1956 Figure: The three inventors of BJT
- 6. Physical structure of BJT • Two types of BJT: i) npn and ii) pnp Figure: Physical structure of BJT Figure: A BJT
- 7. Symbol of BJT Figure: Symbol of BJT
- 8. Physical structure of BJT Width • Collector>Emitter>Base Doping level • Emitter>Collector>Base Why is the width of collector more than the other two parts? Figure: Physical structure of BJT
- 9. Operation of BJT • Regions of operation: BASE-EMITTER JUNCTION COLLECTOR-BASE JUNCTION REGIONS OF OPERATION Forward biased Reverse biased ACTIVE Forward biased Forward biased SATURATION MODE Reverse biased Reverse biased CUT-OFF REGION Reverse biased Forward biased REVERSE ACTIVE Amplifier Closed switch Open switch Switching emitter and collector roles Table: Regions of operation of BJT
- 10. Operation of BJT Emitter-base: Forward biased Collector-base: Reverse biased There is depletion layer across each junction. If Silicon is used then the barrier potential is 0.7 V Here, IE=IC+IB Figure: A common-emitter biasing operation of BJT
- 11. Application of BJT • There are a couple of important applications of BJT • 1)BJT as a switch and • 2)BJT as an amplifier
- 12. BJT as a switch Open switch in cut off region Closed switch in saturation region Figure: Working of BJT as a switch
- 13. BJT as an open switch Vout=VCE=VCC-ICRC Here Vin is varied from 0V i) 0<Vin<VBE CUT-IN Transistor doesn’t conduct IB=0, IC=0 So, Vout=VCC Then the BJT works as an open switch Let RL=RC and Rin=RB Figure: BJT in cut-off mode Figure: Open switch
- 14. BJT as a closed switch ii) Vin>=VBE CUT-IN Then transistor begins conduction. Both IC and IB will flow IB=Vin-VBE/RB IC=βIB V0ut= VCC-ICRC Then the BJT works as a closed switch. Figure: BJT in saturation mode Figure: Closed switch
- 15. BJT as an amplifier • A weak signal is given to the emitter-base junction which is amplified in the output. • Output is received from RL • Change of VS causes change of Vbe and so ib is changed • Vbe Rce ic Vce VR • Small change of VS causes large change of VR • Thus if a weak signal (low amplitude) is given in the input, a large signal (high amplitude) is received in the output. Figure: A common emitter amplifier circuit
- 16. Other uses of BJT BJT can be used as • Logic circuits • Oscillators • Amplifiers • Switch These produce wide applicability in electronic equipment like mobile phones, industrial control, television and radio transmitters
- 17. BJT VS MOSFET BJT switches faster than MOSFET due to less capacitance at the control pin. However, MOSFET is more tolerant to heat (stable to thermal changes) and can simulate a good resistor. At low power and voltages application e.g. less than 10V and 1A, small BJT could be a good choice. VS Figure: A BJT Figure: A MOSFET
- 18. What would the world be like without BJT?
Editor's Notes
- #9: Since collector collects electrons, a huge amount of heat is produced. Thus for better heat dissipation, the width of collector is the greatest.