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Tubes, Transistors and Amplifiers

Tubes, Transistors and Amplifiers Interest

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Tubes, Transistors and Amplifiers

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  1. Tubes, Transistors and Amplifiers CENT-112 Fundamentals of Electricity and Electronics

  2. Interest • In 1947,Bardeen & Brattain at Bell Laboratories created the first amplifier!Shockley (boss), came near to canceling the project. The three shared a Nobel Prize. Bardeen and Brattain continued in research (and Bardeen later won another Nobel). Shockley quit to start a semiconductor company in Palo Alto. It folded, but its staff went on to invent the integrated circuit (the "chip") & to found the Intel Corporation. CENT-112 Fundamentals of Electricity and Electronics

  3. (+) Plate (-) Shield Control Grid (-) Cathode Inert Gas Heater Control Grid: Controls amplification rate & electron flow with bias voltage. Shield: Screen grid- increases electron speed cathode to + plate. Heater: Heats gas to gas amplification state. Inert Gas: Mercury or Argon gas. Tetrode Tube CENT-112 Fundamentals of Electricity and Electronics

  4. Cathode Ray Tube (CRT) 3 Electron Beams (Red, Green, Blue) Phosphor Coated Screen Conductive Coating Grids (-) Cathode (+) Anode The cathode is a heated filament (like light bulb filament) in a vacuum inside a glass tube. The ray is a stream of electrons that naturally pour off a heated cathode into the vacuum. The + anode attracts the electrons pouring off the cathode. In a TV's CRT, the stream of electrons is focused by a focusing anode into a tight beam and then accelerated by an accelerating anode. This tight, high-speed beam of electrons flies through the vacuum in the tube and hits the flat screen at the other end of the tube. This screen is coated with phosphor, which glows when struck by the beam. CENT-112 Fundamentals of Electricity and Electronics

  5. Bipolar Transistors • History • Created in 1948 in the AT&T Bell Laboratories. • Scientists were performing doping experiments on semiconductor material (diodes) and developed a semiconductor device having three (3) PN junctions. CENT-112 Fundamentals of Electricity and Electronics

  6. Bipolar Transistor Construction • NPN / PNP Block Diagrams Emitter Collector N P N Base Emitter Collector P N P Base CENT-112 Fundamentals of Electricity and Electronics

  7. Bipolar Transistor Theory • For any transistor to conduct, two things must occur. • The emitter - base PN junction must be forward biased. • The base - collector PN junction must be reverse biased. CENT-112 Fundamentals of Electricity and Electronics

  8. Bipolar Transistor Biasing (NPN) FB RB Collector - Emitter + N P N Base + CENT-112 Fundamentals of Electricity and Electronics

  9. Bipolar Transistor Biasing (PNP) FB RB Emitter Collector - P N P + Base - CENT-112 Fundamentals of Electricity and Electronics

  10. Bipolar Transistor Operation (PNP) • 90% of the current carriers pass through the reverse biased base - collector PN junction and enter the collector of the transistor. • 10% of the current carriers exit transistor through the base. • The opposite is true for a NPN transistor. CENT-112 Fundamentals of Electricity and Electronics

  11. The transistor below is biased such that there is a degree of forward bias on the base - emitter PN junction. • Any input received will change the magnitude of forward bias & the amount of current flow through the transistor. Amplifier Operation +VCC RC + RB + Q1 0 0 Input Signal Output Signal CENT-112 Fundamentals of Electricity and Electronics

  12. Amplifier Electric Switch Operation • When the input signal is large enough, the transistor can be driven into saturation & cutoff which will make the transistor act as an electronic switch. • Saturation - The region of transistor operation where a further increase in the input signal causes no further increase in the output signal. • Cutoff - Region of transistor operation where the input signal is reduced to a point where minimum transistor biasing cannot be maintained => the transistor is no longer biased to conduct. (no current flows) CENT-112 Fundamentals of Electricity and Electronics

  13. Amplifier Electric Switch Operation • Transistor Q-point • Quiescent point : region of transistor operation where the biasing on the transistor causes operation / output with no input signal applied. • The biasing on the transistor determines the amount of time an output signal is developed. • Transistor Characteristic Curve • This curve displays all values of IC and VCE for a given circuit.It is curve is based on the level of DC biasing that is provided to the transistor prior to the application of an input signal. • The values of the circuit resistors, and VCC will determine the location of the Q-point. CENT-112 Fundamentals of Electricity and Electronics

  14. Transistor Characteristic Curve IB IC 90 uA 80 uA 70 uA Q-Point Saturation 60 uA 50 uA 40 uA 30 uA 20 uA 10 uA 0 uA VCE Cutoff CENT-112 Fundamentals of Electricity and Electronics

  15. When troubleshooting transistors, do the following: • Remove the transistor from the circuit, if possible. • Use a transistor tester, if available, or use a digital multimeter set for resistance on the diode scale. • Test each PN junction separately. ( A “front to back” ratio of at least 10:1 indicates a good transistor). Transistor Maintenance CENT-112 Fundamentals of Electricity and Electronics

  16. Transistor Maintenance Transistor Maintenance Chart • This chart shows the readings for a good transistor. CENT-112 Fundamentals of Electricity and Electronics

  17. Questions Q1. What is the 7 step troubleshooting method? A1. Symptom recognition, symptom elaboration, list possible faulty functions, identify faulty function, identify faulty component, failure analysis, repair, retest. Q2. What was the most difficult problem you ever troubleshot? A2. Various CENT-112 Fundamentals of Electricity and Electronics

  18. Bipolar Transistor Amplifiers • Amplifier Classification • Amplifiers can be classified in three ways: • Type (Construction / Connection) • Common Emitter • Common Base • Common Collector • Bias (Amount of time during each half-cycle output is developed). • Class A, Class B, Class AB, Class C • Operation • Amplifier • Electronic Switch CENT-112 Fundamentals of Electricity and Electronics

  19. Output Signal Flow Path Input Signal Flow Path Common Emitter Schematic +VCC RC + RB + Q1 0 0 Input Signal Output Signal CENT-112 Fundamentals of Electricity and Electronics

  20. Kirchoff Voltage Law • DC Kirchoff Voltage Law Equations and Paths +VCC Base - Emitter Circuit RC IBRB + VBE - VCC = 0 RB Collector - Emitter Circuit Q1 ICRC + VCE - VCC = 0 CENT-112 Fundamentals of Electricity and Electronics

  21. Common Emitter Operation • Positive Going Signal • Negative Going Signal + RC 0 Base becomes more (+) WRT Emitter  Input Signal RB FB   IC  VRC  VC Q1 VOUT ( Less + ) Base becomes less (+) WRT Emitter  + FB  IC Output Signal VRC  VC VOUT ( More + ) 0 CENT-112 Fundamentals of Electricity and Electronics

  22. Common Base Schematic Q1 Input Signal Flow Path RC RE RB + + CC 0 +VCC 0 Output Signal Flow Path CENT-112 Fundamentals of Electricity and Electronics

  23. Kirchoff Voltage Law • DC Kirchoff Voltage Law Equations and Paths Q1 Base - Emitter Circuit RC IBRB + VBE + IERE - VCC = 0 RE RB CC +VCC Collector - Emitter Circuit ICRC + VCE + IERE - VCC = 0 CENT-112 Fundamentals of Electricity and Electronics

  24. Common Base Operation Q1 • Positive Going Signal • Negative Going Signal Base becomes more (+) WRT Emitter  RC RE RB FB  IC VRC  VC CC +VCC VOUT ( More + ) + Base becomes less (+) WRT Emitter  FB  IC 0 VRC  VC 0 VOUT ( Less + ) Input Signal Output Signal CENT-112 Fundamentals of Electricity and Electronics

  25. Common Collector Schematic Output Signal Flow Path +VCC RB + Q1 0 Input Signal + RE 0 Input Signal Flow Path Output Signal CENT-112 Fundamentals of Electricity and Electronics

  26. Kirchoff Voltage Law • DC Kirchoff Voltage Law Equations and Paths +VCC Base - Emitter Circuit IBRB + VBE + IERE - VCC = 0 RB Q1 Collector - Emitter Circuit ICRC + VCE + IERE - VCC = 0 RE CENT-112 Fundamentals of Electricity and Electronics

  27. Common Collector Operation +VCC • Positive Going Signal • Negative Going Signal RB Base becomes more (+) WRT Emitter  FB  IE Q1 VRE  VE VOUT ( More + ) RE Base becomes less (+) WRT Emitter  + + FB  IE 0 0 VRE  VE Input Signal Output Signal VOUT ( Less + ) CENT-112 Fundamentals of Electricity and Electronics

  28. AZAZA VOPINI & House of BEC Common Common Common B E C Av = Voltage Gain Zo = Output Impedance Ap = Power gain Zin = Input Impedance Ai = Current Gain CENT-112 Fundamentals of Electricity and Electronics

  29. Transistor Bias Stabilization • Used to compensate for temperature effects which affects semiconductor operation. As temperature increases, free electrons gain energy and leave their lattice structures which causes current to increase. CENT-112 Fundamentals of Electricity and Electronics

  30. Types of Bias Stabilization • Self Bias: A portion of the output is fed back to the input 180o out of phase. This negative feedback will reduce overall amplifier gain. • Fixed Bias: Uses resistor in parallel with Transistor emitter-base junction. • Combination Bias: This form of bias stabilization uses a combination of the emitter resistor form and a voltage divider. It is designed to compensate for both temperature effects as well as minor fluctuations in supply (bias) voltage. • Emitter Resister Bias: As temperature increases, current flow will increase. This will result in an increased voltage drop across the emitter resistor which opposes the potential on the emitter of the transistor. CENT-112 Fundamentals of Electricity and Electronics

  31. Self Bias Schematic +VCC + + + RC o o Initial Input Self Bias Feedback + RB Q1 o + VOUT = o Resulting Input CENT-112 Fundamentals of Electricity and Electronics

  32. Emitter Bias Schematic +VCC DC Component AC Component RC + RB ++ + + Q1 o - o VOUT Initial Input + CE RE - CENT-112 Fundamentals of Electricity and Electronics

  33. Combination Bias Schematic +VCC DC Component AC Component RC + RB1 ++ + + Q1 o o RB2 - VOUT Initial Input + CE RE - CENT-112 Fundamentals of Electricity and Electronics

  34. Amplifier Frequency Response • The range or band of input signal frequencies over which an amplifier operates with a constant gain. • Amplifier types and frequency response ranges. • Audio Amplifier • 15 Hz to 20 KHz • Radio Frequency (RF) Amplifier • 10 KHz to 100,000 MHz • Video Amplifier (Wide Band Amplifier) • 10 Hz to 6 MHz CENT-112 Fundamentals of Electricity and Electronics

  35. Class ‘A’ Amplifier Curve IB IC 90 uA 80 uA 70 uA Saturation 60 uA 50 uA 40 uA 30 uA Q-Point 20 uA 10 uA 0 uA VCE Cutoff CENT-112 Fundamentals of Electricity and Electronics

  36. Class ‘B’ Amplifier Curve IB IC 90 uA 80 uA 70 uA Saturation 60 uA 50 uA 40 uA 30 uA Q-Point 20 uA 10 uA 0 uA VCE Cutoff CENT-112 Fundamentals of Electricity and Electronics

  37. Class ‘AB’ Amplifier Curve Can be used for guitar distortion. IB IC 90 uA 80 uA 70 uA Saturation 60 uA 50 uA 40 uA 30 uA 20 uA Q-Point 10 uA 0 uA VCE Cutoff CENT-112 Fundamentals of Electricity and Electronics

  38. Class ‘C’ Amplifier Curve IB IC 90 uA 80 uA 70 uA Saturation 60 uA 50 uA 40 uA 30 uA 20 uA 10 uA 0 uA Q-Point VCE Cutoff CENT-112 Fundamentals of Electricity and Electronics

  39. Amplifier Coupling Methods • Direct: The output of the first stage is directly connected to the input of the second stage. Best Frequency Response - No frequency sensitive components. • Impedance (LC) Coupling: Similar to RC coupling but an inductor is used in place of the resistor. Not normally used in Audio Amplifiers. • RC Coupling: Most common form of coupling used. Poor Frequency Response. • Transformer Coupling: Most expensive form coupling used. Mainly used as the last stage or power output stage of a string of amplifiers. CENT-112 Fundamentals of Electricity and Electronics

  40. +VCC2 Direct Coupling Schematic RC2 +VCC1 RB2 RC1 Q2 RB1 Q1 CENT-112 Fundamentals of Electricity and Electronics

  41. +VCC2 RC Coupling Schematic RC2 +VCC1 RB2 RC1 Q2 CC RB1 Q1 CENT-112 Fundamentals of Electricity and Electronics

  42. +VCC2 Impedance Coupling Schematic RC2 +VCC1 RB2 Q2 CC RB1 Q1 CENT-112 Fundamentals of Electricity and Electronics

  43. +VCC2 Transformer Coupling Schematic RC2 +VCC1 RB2 RC1 Q2 RB1 T1 Q1 CENT-112 Fundamentals of Electricity and Electronics

  44. Silicon Controlled Rectifiers • Silicon Controlled Rectifiers (SCR) • Construction • Block Diagram Anode Cathode P N P N Left Floating Region Gate CENT-112 Fundamentals of Electricity and Electronics

  45. OPAMP Voltage Regulators - + Vin Vout CENT-112 Fundamentals of Electricity and Electronics

  46. SCR Schematic Anode Cathode Gate CENT-112 Fundamentals of Electricity and Electronics

  47. SCR Bias • When the SCR is forward biased and a gate signal is applied, the lightly doped gate region’s holes will fill with the free electrons forced in from the cathode. FB FB Anode Cathode - P N P N + RB Gate + CENT-112 Fundamentals of Electricity and Electronics

  48. SCR Operation • Acts as an electronic switch • Essentially a rectifier diode which has a controllable “Turn - on” point. Can be switched approximately 25,000 times per second. • Once the SCR conducts, the gate signal can be removed. The difference in potential across the anode & cathode of the SCR will maintain current flow. • When the voltage across the SCR drops to a level below the “Minimum Holding” value, the PN junctions will reform and current flow through the SCR will stop. CENT-112 Fundamentals of Electricity and Electronics

  49. SCR Phase Control • The term Phase Control refers to a process where varying the timing of the gate signal to an SCR will vary the length of time that the SCR conducts. • This will determine the amount of Voltage or Power delivered to a load. CENT-112 Fundamentals of Electricity and Electronics

  50. Unijunction Transistors (UJT) • Construction: Originally called “Double-based Diodes.” • “P” Type material doped into the “N” type base material. • Placement of the Emitter into the Base determines the voltage level (%) at which the the UJT fires. • This % is called the “Intrinsic Standoff Ratio ( ).” • Once constructed, the Intrinsic Standoff Ratio cannot be changed. • The actual voltage value at which the UJT fires is determined by the amount of source voltage applied. CENT-112 Fundamentals of Electricity and Electronics

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