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Transistor
- 1. TRANSISTOR EC&C SUBJECT PREPARED BY: D.H.SHUKLA
- 2. WHY WE NEEDELECTRONICS • Electronics is widely used in information processing, telecommunication, and signal processing. The ability of electronic devices to act as switches makes digital information- processing possible. • Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements; such a circuit is described as an electronic circuit.
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- 16. WHAT IS ATRANSISTOR? • Semiconductors: ability to change from conductor to insulator • Can either allow current or prohibit current to flow • Useful as a switch, but also as an amplifier • Essential part of many technological advances
- 17. A BRIEF HISTORY •Guglielmo Marconi invents radio in 1895 • Problem: For long distance travel, signal must be amplified • Lee De Forest improves on Fleming’s original vacuum tube to amplify signals • Made use of third electrode • Too bulky for most applications
- 18. THE TRANSISTOR ISBORN • Bell Labs (1947): Bardeen, Brattain, and Shockley • Originally made of germanium • Current transistors made of doped silicon
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- 21. • Construction • twopolarities: npn and pnp
- 24. RECALL P-N JUNCTION PN W Vappl > 0 -+ N P W Vappl < 0 -+ Forward bias, + on P, - on N (Shrink W, Vbi) Allow holes to jump over barrier into N region as minority carriers Reverse bias, + on N, - on P (Expand W, Vbi) Remove holes and electrons away from depletion region I V I V
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- 32. TRANSISTOR CHARACTERISTICS • CommonBase : Input & Output Characteristics
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- 38. CONCLUSION CB CE CC InputResistance Very low Medium High Output Resistance Very high Medium Low Current Gain Less then 1 More then 1 More then 1 Power gain Lower then CE High Higher then CB
- 39. QUESTIONS • Explain workingof NPN transistor • Draw the input and output characteristics of common emitter (CE) configuration. • Compare three configurations of transistor.
- 42. DC CURRENT GAIN •𝛼 𝑑𝑐 = 𝐼𝑐 𝐼𝐸 (Ratio of Collector Current to Emitter Current) • 𝑑𝑐 = 𝐼𝑐 𝐼𝐵 (Ratio of Collector Current to Base Current) • 𝛼 𝑑𝑐= hFB • 𝑑𝑐 = hFB
- 43. AC CURRENT GAIN(WHEN USE AS AMPLIFIER) • 𝛼 𝑎𝑐 = 𝐼𝑐 𝐼𝐸 (𝑊ℎ𝑒𝑛 𝑉𝐶𝐵 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡) • 𝑎𝑐 = 𝐼𝑐 𝐼𝐵 (When VCE Constant)
- 44. RELATION BETWEEN 𝛼𝑑𝑐 & 𝑑𝑐
- 45. CONTINUE… • 𝛽𝑑𝑐 = 𝛼𝑑𝑐 1−𝛼 𝑑𝑐 • 𝛼 𝑑𝑐 = 𝛽𝑑𝑐 1+𝛽𝑑𝑐
- 46. 𝑅𝑒𝑙𝑎𝑡𝑖𝑜𝑛 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝛼𝑎𝑐 AND 𝑎𝑐 • IE = IC + IB • 𝐼𝐸 = 𝐼C + 𝐼𝐵 (FOR AC) • DIVIDED BY 𝐼𝑐 • 𝐼𝐸 𝐼𝐶 = 1 + 𝐼𝐵 𝐼𝐶 • 1 𝛼 = 1+ 1 𝛽 • 𝛽𝑑𝑐 = 𝛼 𝑑𝑐 1−𝛼 𝑑𝑐 • 𝛼 𝑑𝑐 = 𝛽𝑑𝑐 1+𝛽𝑑𝑐
- 50. QUESTION • Define and derive relation between two
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- 52. DIFFERENT AMPLIFIER INMARKET
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- 57. SOME PARAMETERS • Voltagegain Av = Amplitude of output voltage ÷ Amplitude of input voltage. • Current gain Ai = Amplitude of output current ÷ Amplitude of input current. • Power gain Ap = Signal power out ÷ Signal power in.
- 58. • Explain howtransistor acts as an amplifier. • Define amplifier. Explain common emitter amplifier.
- 59. TRANSISTOR BIASING • Whatis Transistor biasing • Transistor biasing is the process of setting a transistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by the transistor.
- 60. NEED OF TRANSISTORBIASING 1. To make a operating point at a centre of active region so for that transistor will not go in saturation region 2. Operating point will not change with respect to temperature 3. If we change a transistor but parameters of transistor will not be change
- 61. METHOD OF BIASING •We can give a VBB,Vcc, VEE using only one battery Here are a methods 1. Fixed biasing 2. Collector to Base Biasing 3. Emitter resistor Biasing 4. Voltage divider biasing
- 62. FIXED BIASING • HereRB> RC then IC >IB • If Vcc and RB is fixed so “Base current IB is fixed that’s why is biasing is called fixed biasing “
- 63. ADVANTAGE & DISADVANTAGE •Advantages: - 1. Circuit is simple 2. Less component Require 3. Resistor will not connect between base to emitter so input resistance will not goes down so circuit will not load to source • Disadvantages: - 1. If temperature is increased then ICBO and ICEO increased then IC increased so temperature is also increased 2. If we change a transistor then all parameters are change and operating points also change
- 64. COLLECTOR TO BASE(COLLECTOR FEEDBACK BIAS) • Here IB is depending upon IC • So if we increased a Ic then IB is also increased • Now to reduce a Ic then Rc is increased consequences voltage drop across Rc increased so VcB decreases • That’s why if temperature is goes up but stability is
- 65. ADVANTAGE & DISADVANTAGE •Advantages: - 1. Circuit is simple 2. Less component Require 3. Stability factor is good • Disadvantages: - 1. If temperature is increased then little bit of operating point decreased 2. Here RB is connected between collector and base so feedback is given by it. So negative feedback is there so gain is reduced
- 66. EMITTER RESISTOR BIAS(EMITTER FEEDBACKBIAS) • Here a one Resistor is connected with emitter • Suppose if temperature is increased then collector current Ic is increased then so voltage drop across Rc and RB increased • This drop opposite to base current so base current is reduce and so collector current also reduce • That’s why no change in operating point and amplification factor
- 67. ADVANTAGE & DISADVANTAGE •Advantages: - 1. No change in operating point and if temperature is increased • Disadvantages: - 1. Feedback is negative so gain is reduces 2. Costly circuit Note:- To increase a gain then connect a capacitor across a base resistor A value of capacitor is 10 times base resistor value
- 68. VOLTAGE DIVIDER BIASING •Here R1 and R2 are Biasing resistor so Vb is fixed • In this biasing operating point will constant with respect to temperature • 𝐼1 = 𝐼2 + 𝐼𝐵 If we reduces a IB then I1 = I2 so base potential is fixed • VE = VB – VBE • So IE = VE/RE • Also IB is small then IC = IE • And VCE = VCC – IC(RC – RE)
- 69. ADVANTAGE & DISADVANTAGE •Advantages: - 1. No change in operating point and if temperature is increased 2. Q point value is stable • Disadvantages: - 1. Costly because required more component 2. Stability factor is high therefore chance to thermal runaway
- 70. QUESTIONS • State thevarious biasing methods for transistor and explain any one • Explain working of Voltage dividertype biasing with it circuit diagram
- 71. CASCADING AMPLIFIER • Whenwe want to a huge value of amplification then we make a cascade connection between more then two amplifier, • An Input of A2 is depending upon output of A1, A1 A2 A3 Input Output
- 72. GAIN OF CASCADEAMPLIFIER • Suppose gain of A1= Av1, A2 = Av2, A3 = Av3 • Total gain is Av = Av1 x Av2 x Av3 , If Av1 = 30, Av2 = 60, Av3 = 70 • Total = 30 x 60 x 70 = 1,26000 • Suppose this gain is defined in dB ( Decibel ) then • AdB = AdB1 + AdB2 + AdB3 AdB = 20 log10 AV
- 73. LIMITATION OF CASCADEAMPLIFIER •High cost •Decrease a Bandwidth because lower cut-off frequency increases and higher cut-off frequency is decreases •It load a next stage
- 74. REQUIREMENTS FOR CASCADE •Onedc bias stage cannot effect an other dc bias stage •No any signal loss in coupling if it do then gain will be reduce
- 75. METHODS TO CASCADE •DirectCoupled •RC Coupled •LC Coupled •Transformer Couple
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- 77. CONTINUE…. • In thismethod a two amplifier connected with simple wires • An output signal is produce at collector of amplifier1 that directly gives to base to another amplifier • When input signal value is small and need to small amplification then this method is helpful
- 78. ADVANTAGES & DISADVANTAGES •Advantage • 1. size is small 2. Low cost 3.Easy to design • Dis-Advantages • 1. 1st amplifier bias is affect a 2nd amplifier so need to separate VCC supply • 2. Effect of temperature at output • Application :- Thermocouple
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- 80. CONTINUE… Advantages 1. Less spacerequired 2. Less cost 3. Use for medium Frequency Disadvantages 1. Coupling Capacitor signal Loss 2. For low signal amplification need Application :- Radio, T.V.,etc.
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- 82. CONTINUE…. Advantages 1. Small dcvoltage drop occurs so totally Vcc voltage utilised in transistor 2. If impedance of choke is more then signal gain will be more Disadvantages :- 1. Required More Space 2. Choke reactance will change with respect to frequency so response is not same
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- 84. CONTINUE… Advantages 1. Low dcVoltage drop 2. Here Transformer in place of Rc so low power loss 3. No coupling capacitor so no loss in signal 4. Impedance matching can be done Disadvantages : 1. Weight and size is more 2. Costly 3. Frequency response not clear
- 85. COMPARISON OF CASCADEAMPLIFIER Parameters Direct Coupling RC Coupling LC Coupling Transformer Coupling Required Space Less then RC Coupling Less More More Weight Lesser Less More More Frequency Response Good Better Constant AF Range Not good Impedance Matching Good Not good Poor Good Cost Lesser Less More More Application Amplify a Low value of Signal Voltage Amplifier Not use Power amplifier and Tunde Amplifier
- 86. QUESTION • Explain necessityof cascading of amplifier. • Compare a different types of cascade Amplifier
- 87. POWER AMPLIFIER Power Amplifier SignalWith Less Power Signal With More Power
- 88. WHAT IS POWERAMPLIFIER • An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones
- 89. COMPARISON BETWEEN VOLTAGE& POWER AMPLIFIER Voltage Amplifier Power Amplifier In voltage amplifier the amplitude of input A.C signal is small. In power amplifier the amplitude of input A.C signal is large. In voltage amplifier the collector current is low, about 1 mA. In power amplifier the collector current is very high above greater than 100mA. The transistor used can dissipate less heat produced during its operation. The transistor used can dissipate more heat produced as compared to voltage amplifier during its operation. RC coupling is used in voltage amplifier. In power amplifier invariably transformer coupling is used. The transistor used has thin base to handle low current. The transistor used has thick base to handle large current. In voltage amplifier the A.C power output is low. In power amplifier the A.C power output is high. The physical size of transistor used is usually small and is known as low or medium power transistor. The physical size of transistor used is usually large and is known as power transistor. In voltage amplifier the collector load has high resistance, typically 4kΩ to 10kΩ. In power amplifier the collector load has low resistance, typically 5Ω to 20Ω.
- 90. CLASSIFICATION OF POWERAMPLIFIER
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- 94. CLASS A AMPLIFIER •The most commonly used type of power amplifier configuration is the Class A Amplifier. The Class A amplifier is the simplest form of power amplifier that uses a single switching transistor in the standard common emitter circuit configuration as seen previously to produce an inverted output. The transistor is always biased “ON” so that it conducts during one complete cycle of the input signal waveform producing minimum distortion and maximum amplitude of the output signal. • This means then that the Class A Amplifier configuration is the ideal operating mode, because there can be no crossover or switch-off distortion to the output waveform even during the negative half of the cycle
- 95. TYPES OF CLASSA AMPLIFIER • Single stage 1. Series Fed Class A • Transformer Coupled Amplifier • Darlington Amplifier
- 96. SERIES FED CLASSA AMPLIFIERThe simple fixed-bias circuit connection shown in the figure below can be used to discuss the main features of a series fed class A amplifier. The only differences between this circuit and the small-signal version considered previously are that the signals handled by the large-signal circuit are in the range of volts and the transistor used is a power transistor that is capable of operating in the range of a few to tens of watts.
- 97. OPERATION • SupposeInput is not given then through biasing IB Current is flow, Consequences Ic will flow so we get VCE voltage . • Now decide a value of RB that can operate a transistor in active region, So Q point will be in middle • When we give an input then current will be change and voltage drop across Rc is increased So collector current will be in 360 degree
- 98. NEED OF TRANSFORMERIN CLASS A AMPLIFIER • One of the main applications for audio frequency transformers is in impedance matching. Audio transformers are ideal for balancing amplifiers and loads together that have different input/output impedances in order to achieve maximum power transfer. • We know that for a transformer, the ratio between the number of coil turns on the primary winding (NP) to the number of coil turns on the secondary winding (NS) is called the “turns ratio”. Since the same amount of voltage is induced within each single coil turn of both windings, the primary to secondary voltage ratio (VP/VS) will therefore be the same value as the turns ratio.
- 99. TRANSFORMER COUPLED CLASSA AMPLIFIER
- 100. CLASS B PUSH-PULLAMPLIFIER
- 101. DISTORTION • Types ofDistortion • 1. Frequency Distortion • 2. Phase Distortion • 3. Amplitude Distortion
- 102. QUESTIONS • Compare voltageamplifier and power amplifier. • Compare class A, B, AB and C amplifiers. • Draw the circuit of class B push-pull amplifier and explain its working. • Explain different types of distortions occurred in amplifier.
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