More Related Content
Similar to ECE312_lec03.pdf
Similar to ECE312_lec03.pdf (20)
Recently uploaded
Recently uploaded (20)
ECE312_lec03.pdf
- 1. Lecture #3 BJT Biasing Circuits Instructor: Dr. Ahmad El-Banna Benha University Faculty of Engineering at Shoubra October 2014 ECE-312 Electronic Circuits (A) © Ahmad El-Banna
- 2. Agenda Operating Point Transistor DC Bias Configurations Design Operations Various BJT Circuits Troubleshooting Techniques & Bias Stabilization Practical Applications 2 ECE-312 , Lec#3 , Oct 2014 © Ahmad El-Banna
- 3. Introduction • Any increase in ac voltage, current, or power is the result of a transfer of energy from the applied dc supplies. • The analysis or design of any electronic amplifier therefore has two components: a dc and an ac portion. 3 ECE-312 , Lec#3 , Oct 2014 • Basic Relationships/formulas for a transistor: • Biasing means applying of dc voltages to establish a fixed level of current and voltage. >>> Q-Point © Ahmad El-Banna
- 4. Operating Point • For transistor amplifiers the resulting dc current and voltage establish an operating point on the characteristics that define the region that will be employed for amplification of the applied signal. • Because the operating point is a fixed point on the characteristics, it is also called the quiescent point (abbreviated Q-point). 4 ECE-312 , Lec#3 , Oct 2014 Transistor Regions Operation: 1. Linear-region operation: Base–emitter junction forward-biased Base–collector junction reverse-biased 2. Cutoff-region operation: Base–emitter junction reverse-biased Base–collector junction reverse-biased 3.Saturation-region operation: Base–emitter junction forward-biased Base–collector junction forward-biased © Ahmad El-Banna
- 5. TRANSISTOR DC BIAS CONFIGURATIONS • Fixed-Bias Configuration • Emitter-Bias Configuration • Voltage-Divider Bias Configuration • Collector Feedback Configuration • Emitter-Follower Configuration • Common-Base Configuration • Miscellaneous Bias Configurations 5 ECE-312 , Lec#3 , Oct 2014 © Ahmad El-Banna
- 6. Fixed-Bias Configuration 6 ECE-312 , Lec#3 , Oct 2014 • Fixed-bias circuit. • DC equivalent ct. • Base–emitter loop. • Collector–emitter loop. © Ahmad El-Banna
- 8. Fixed-Bias Configuration ... • Transistor Saturation 8 ECE-312 , Lec#3 , Oct 2014 • Determining ICsat for the fixed-bias configuration. • Determining ICsat • Saturation regions: (a) Actual (b) approximate. © Ahmad El-Banna
- 9. Fixed-Bias Configuration ... 9 ECE-312 , Lec#3 , Oct 2014 • Load Line Analysis © Ahmad El-Banna
- 10. Emitter-Bias Configuration 10 ECE-312 , Lec#3 , Oct 2014 • Base-Emitter Loop • DC equivalent ct • BJT bias circuit with emitter resistor. © Ahmad El-Banna
- 11. Emitter-Bias Configuration 11 ECE-312 , Lec#3 , Oct 2014 Collector-Emitter Loop © Ahmad El-Banna
- 12. Emitter-Bias Configuration • Improved bias stability (check example 4.5) 12 ECE-312 , Lec#3 , Oct 2014 The addition of the emitter resistor to the dc bias of the BJT provides improved stability, that is, the dc bias currents and voltages remain closer to where they were set by the circuit when outside conditions, such as temperature and transistor beta, change. • Saturation Level • Load Line Analysis © Ahmad El-Banna
- 13. Voltage-Divider Configuration 13 ECE-312 , Lec#3 , Oct 2014 • Exact Analysis • Voltage-divider bias configuration. • DC components of the voltage-divider configuration. © Ahmad El-Banna
- 14. Voltage-Divider Configuration 14 ECE-312 , Lec#3 , Oct 2014 • Approximate Analysis • Transistor Saturation • Load-Line Analysis © Ahmad El-Banna
- 16. Collector Feedback Configuration 16 ECE-312 , Lec#3 , Oct 2014 • DC bias circuit with voltage feedback. • Base–Emitter Loop • Collector–Emitter Loop © Ahmad El-Banna
- 17. Collector Feedback Configuration 17 ECE-312 , Lec#3 , Oct 2014 • Saturation Conditions Using the approximation I’C = IC • Load-Line Analysis Continuing with the approximation I’C = IC results in the same load line defined for the voltage-divider and emitter-biased configurations. The level of IBQ is defined by the chosen bias configuration. © Ahmad El-Banna
- 18. Emitter-Follower Configuration 18 ECE-312 , Lec#3 , Oct 2014 i/p ct o/p ct • dc equivalent ct • Common-collecter (emitter-follower) configuration. © Ahmad El-Banna
- 19. Common-Base Configuration 19 ECE-312 , Lec#3 , Oct 2014 • i/p ct • Determining VCB & VCE • Common-base configuration © Ahmad El-Banna
- 24. Design Operations 24 ECE-312 , Lec#3 , Oct 2014 • Discussions thus far have focused on the analysis of existing networks. All the elements are in place, and it is simply a matter of solving for the current and voltage levels of the configuration. • The design process is one where a current and/or voltage may be specified and the elements required to establish the designated levels must be determined. • The design sequence is obviously sensitive to the components that are already specified and the elements to be determined. If the transistor and supplies are specified, the design process will simply determine the required resistors for a particular design. • Once the theoretical values of the resistors are determined, the nearest standard commercial values are normally chosen and any variations due to not using the exact resistance values are accepted as part of the design. © Ahmad El-Banna
- 26. Design Operations Example.. 26 ECE-312 , Lec#3 , Oct 2014 • Design of a Current-Gain-Stabilized (Beta-Independent) Circuit © Ahmad El-Banna
- 27. VARIOUS BJT CIRCUITS • MULTIPLE BJT NETWORKS • CURRENT MIRRORS • CURRENT SOURCE CIRCUITS • Bipolar Transistor Constant-Current Source • Transistor/Zener Constant-Current Source • PNP TRANSISTORS • TRANSISTOR SWITCHING NETWORKS 27 ECE-312 , Lec#3 , Oct 2014 © Ahmad El-Banna
- 28. MULTIPLE BJT NETWORKS 28 ECE-312 , Lec#3 , Oct 2014 • R–C coupling • Darlington configuration © Ahmad El-Banna
- 30. MULTIPLE BJT NETWORKS… 30 ECE-312 , Lec#3 , Oct 2014 • Feedback Pair © Ahmad El-Banna
- 31. MULTIPLE BJT NETWORKS…. 31 ECE-312 , Lec#3 , Oct 2014 • Direct Coupled © Ahmad El-Banna
- 33. CURRENT SOURCE CIRCUITS 33 ECE-312 , Lec#3 , Oct 2014 • Bipolar Transistor Constant-Current Source • Transistor/Zener Constant-Current Source © Ahmad El-Banna
- 37. TROUBLESHOOTING TECHNIQUES • For an “on” transistor, the voltage VBE should be in the neighborhood of 0.7 V. • For the typical transistor amplifier in the active region, VCE is usually about 25% to 75% of VCC . 37 ECE-312 , Lec#3 , Oct 2014 © Ahmad El-Banna
- 38. BIAS STABILIZATION • The stability of a system is a measure of the sensitivity of a network to variations in its parameters. • In any amplifier employing a transistor the collector current IC is sensitive to each of the following parameters: 38 ECE-312 , Lec#3 , Oct 2014 © Ahmad El-Banna
- 39. BIAS STABILIZATION .. S(Ico) 39 ECE-312 , Lec#3 , Oct 2014 • fixed-bias configuration the level of IC would continue to rise with temperature, with IB maintaining a fairly constant value—a very unstable situation. • emitter-bias configuration there is a reaction to an increase in IC that will tend to oppose the change in bias conditions. • feedback configuration a stabilizing effect as described for the emitter-bias configuration. • voltage-divider bias The most stable of the configurations © Ahmad El-Banna
- 40. BIAS STABILIZATION .. S(VBE)& S(β) 40 ECE-312 , Lec#3 , Oct 2014 For fixed-bias © Ahmad El-Banna
- 41. PRACTICAL APPLICATION • BJT Diode Usage and Protective Capabilities • Relay Driver • Light Control • Maintaining a Fixed Load Current • Alarm System with a CCS • Voltage Level Indicator • Logic Gates 41 ECE-312 , Lec#3 , Oct 2014 © Ahmad El-Banna
- 42. Practical Application 42 ECE-312 , Lec#3 , Oct 2014 • BJT Diode Usage and Protective Capabilities • Relay Driver © Ahmad El-Banna
- 43. Practical Application.. 43 ECE-312 , Lec#3 , Oct 2014 • Maintaining a Fixed Load Current • Light Control © Ahmad El-Banna
- 44. Practical Application… 44 ECE-312 , Lec#3 , Oct 2014 • Alarm System with a CCS • Voltage Level Indicator © Ahmad El-Banna
- 45. Practical Application…. 45 ECE-312 , Lec#3 , Oct 2014 • Logic Gates © Ahmad El-Banna
- 46. • For more details, refer to: • Chapter 4 at R. Boylestad, Electronic Devices and Circuit Theory, 11th edition, Prentice Hall. • The lecture is available online at: • https://speakerdeck.com/ahmad_elbanna • For inquires, send to: • ahmad.elbanna@fes.bu.edu.eg • ahmad.elbanna@ejust.edu.eg 46 ECE-312 , Lec#3 , Oct 2014 © Ahmad El-Banna