Basic Electronics UNIt1 PPT
- 1. MATRUSRI ENGINEERING COLLEGE DEPARTMENT OF INORMATION TECHNOLOGY SUBJECT NAME: BASIC ELECTRONICS FACULTY NAME: K PRAVEEN MATRUSRI ENGINEERING COLLEGE
- 2. BASIC ELECTRONICS COURSE OBJECTIVES: 1.To understand the characteristics of diodes and transistor configurations. 2.To understand the design concepts of biasing of BJT and FET. 3.To understand the design concepts of feedback amplifiers and oscillators. 4. To study the design concepts of OP Amp and data converters MATRUSRI ENGINEERING COLLEGE
- 3. BASIC ELECTRONICS COURSE OUTCOMES: On successful completion of this course, the students will be able to: 1.Study and analyse the rectifier and regulator circuits. 2.Study and analyse the performance of BJTs, FETs on the basis of their operation and working. 3.Ability to analyse and design oscillator circuits. 4.Ability to analyse different logic gates and multivibrator circuits. 5.Ability to analyse different data acquisition systems. MATRUSRI ENGINEERING COLLEGE
- 4. UNIT-I OUTCOMES: To understand the semiconductor materials that are suitable for electronic devices To study the properties of materials for electronic devices To understand the biasing of diode Able to design Diode circuit Able to apply some types of diodes MATRUSRI ENGINEERING COLLEGE Characteristics of PN junction: half wave rectifier, full wave rectifiers, filters, ripple, regulation, TUF and efficiency , Zener diode and Zener diode regulators.CRT construction and CRO applications..
- 5. MATRUSRI ENGINEERING COLLEGE OUTCOMES: To understand the biasing of diode Able to design Diode circuit Able to apply some types of diodes MODULE-I MATRUSRI ENGINEERING COLLEGE CONTENTS: Characteristics of PN junction: half wave rectifier, full wave rectifiers Filters, ripple, regulation, TUF and efficiency
- 6. Boron and gallium each have only three outer electrons. When mixed into the silicon lattice, they form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name P-type. Holes can conduct current. A hole happily accepts an electron from a neighbor, moving the hole over a space. P-type silicon is a good conductor. MATRUSRI ENGINEERING COLLEGE PN Junction formation P-Type Doping
- 7. MATRUSRI ENGINEERING COLLEGE Phosphorus and arsenic each have five outer electrons, so they're out of place when they get into the silicon lattice. The fifth electron has nothing to bond to, so it's free to move around. It takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. N-type silicon is a good conductor. Electrons have a negative charge, hence the name N-type. PN Junction formation N-Type Doping
- 8. MATRUSRI ENGINEERING COLLEGE PN Junction We create a p-n junction by joining together two pieces of semiconductor, one doped n-type, the other p-type. In the n-type region there are extra electrons and in the p-type region, there are holes from the acceptor impurities .
- 9. MATRUSRI ENGINEERING COLLEGE PN Junction In the p-type region there are holes from the acceptor impurities and in the n- type region there are extra electrons. When a p-n junction is formed, some of the electrons from the n-region which have reached the conduction band are free to diffuse across the junction and combine with holes. Filling a hole makes a negative ion and leaves behind a positive ion on the n-side. A space charge builds up, creating a depletion region.
- 10. This causes a depletion zone to form around the junction (the join) between the two materials. This zone controls the behavior of the diode. MATRUSRI ENGINEERING COLLEGE PN Junction
- 11. Forward biasing the p-n junction drives holes to the junction from the p- type material and electrons to the junction from the n-type material. At the junction the electrons and holes combine so that a continuous current can be maintained. MATRUSRI ENGINEERING COLLEGE Forward Biasing
- 12. The application of a reverse voltage to the p-n junction will cause a transient current to flow as both electrons and holes are pulled away from the junction. When the potential formed by the widened depletion layer equals the applied voltage, the current will cease except for the small thermal current. MATRUSRI ENGINEERING COLLEGE Reverse Biasing
- 13. MATRUSRI ENGINEERING COLLEGE V-I Characteristics When forward-biased, there is a small amount of voltage necessary to get the diode going. In silicon, this voltage is about 0.7 volts. This voltage is needed to start the hole-electron combination process at the junction. When reverse-biased, an ideal diode would block all current. A real diode lets perhaps 10 microamps through -- not a lot, but still not perfect. Usually, the breakdown voltage is a lot more voltage than the circuit will ever see, so it is irrelevant.
- 14. where IS = reverse saturation current (A) vD = voltage applied to diode (V) q = electronic charge (1.60 x 10-19 C) k = Boltzmann’s constant (1.38 x 10-23 J/K) T = absolute temperature n = non ideality factor (dimensionless) VT = kT/q = thermal voltage (V) (25 mV at room temp.) IS is typically between 10-18 and 10-9 A, and is strongly temperature dependent due to its dependence on ni 2. The non ideality factor is typically close to 1, but approaches 2 for devices with high current densities. It is assumed to be 1 in this text. Diode current equation MATRUSRI ENGINEERING COLLEGE
- 15. IS, the reverse bias saturation current for an ideal p-n diode is given as where • IS is the reverse bias saturation current, • e is elementary charge • A is the cross-sectional area • Dp,n are the diffusion coefficients of holes and electrons, respectively, • ND,A are the donor and acceptor concentrations at the n side and p side,respectively, • ni is the intrinsic carrier concentration in the semiconductor material, • τp,n are the carrier lifetimes of holes and electrons, respectively. MATRUSRI ENGINEERING COLLEGE Diode current equation(contd…)
- 16. Diode Current for Reverse, Zero, and Forward Bias • Reverse bias: • Zero bias: • Forward bias: i D I Sexp v D nV T 1 I S0 1 I S i D I Sexp v D nV T 1 I S1 1 0 i D I Sexp v D nV T 1 I S exp v D nV T MATRUSRI ENGINEERING COLLEGE
- 43. MODULE-II CONTENTS: Zener diode and Zener diode regulators.CRT construction and CRO applications. OUTCOMES: To understand the operation, performance of Zener diode To understand the operation and applications of CRO
- 44. Breakdown in diodes • Avalanche Breakdown Si diodes with VZ greater than about 5.6 volts breakdown according to an avalanche mechanism. As the electric field increases, accelerated carriers begin to collide with fixed atoms. As the reverse bias increases, the energy of the accelerated carriers increases, eventually leading to ionization of the impacted ions. The new carriers also accelerate and ionize other atoms. This process feeds on itself and leads to avalanche breakdown. MATRUSRI ENGINEERING COLLEGE
- 45. Breakdown in diodes (cont.) • Zener Breakdown Zener breakdown occurs in heavily doped diodes. The heavy doping results in a very narrow depletion region at the diode junction. Reverse bias leads to carriers with sufficient energy to tunnel directly between conduction and valence bands moving across the junction. Once the tunneling threshold is reached, additional reverse bias leads to a rapidly increasing reverse current. • Breakdown Voltage Temperature Coefficient Temperature coefficient is a quick way to distinguish breakdown mechanisms. Avalanche breakdown voltage increases with temperature, whereas Zener breakdown decreases with temperature. For silicon diodes, zero temperature coefficient is achieved at approximately 5.6 V. MATRUSRI ENGINEERING COLLEGE
- 46. 46 A typical V-I curve for a Zener diode. A Zener diode reference circuit. The Zener diode is made to operate under reverse bias once a sufficiently high voltage has been reached. The V-I curve of a Zener diode is shown in Figure. Notice that under reverse bias and low voltage the current assumes a low negative value, just as in a normal pn-junction diode. But when a sufficiently large reverse bias voltage is reached, the current increases at a very high rate. Zener Diode MATRUSRI ENGINEERING COLLEGE
- 47. Voltage Regulator Using the Zener Diode The Zener diode keeps the voltage across load resistor RL constant. For Zener breakdown operation, IZ > 0. I S V S V Z R ( 20 5 ) V 5 k 3 mA I L V Z R L 5 V 5 k 1 mA | I Z I S I L 2 mA I Z V S R V Z 1 R 1 R L 0 |R L R V S V Z 1 R min For proper regulation, Zener current must be positive. If the Zener current < 0, the Zener diode no longer controls the voltage across the load resistor and the voltage regulator is said to have “dropped out of regulation”. MATRUSRI ENGINEERING COLLEGE
- 48. Line and Load Regulation Line regulation characterizes how sensitive the output voltage is to input voltage changes. (Circuit on previous page, Figure 3.41) Line Regulation dV L dV S mV/V For a fixed load curren Line Regulation = R Z R + R Z Load regulation characterizes how sensitive the output voltage is to changes in load current withdrawn from regulator. Load regulation is the Thévenin equivalent resistance looking back into the regulator from the load terminals. Load Regulation dV L dI L For changes in load Load Regul R Z R MATRUSRI ENGINEERING COLLEGE
- 50. CRO MATRUSRI ENGINEERING COLLEGE Cathode ray tube - it is the heart of the oscilloscope. When the electrons emitted by the electron gun strikes the phosphor screen, a visual signal is displayed on the CRT. Vertical amplifier - the input signals are amplified by the vertical amplifier. Usually, the vertical amplifier is a wide band amplifier which passes the entire band of frequencies. Delay line - as the name suggests, this circuit is used to delay the signal for a period of time in the vertical section of CRT. The input signal is not applied directly to the vertical plates because the part of the signal gets lost, when the delay time is not used. Therefore, the input signal is delayed by a period of time. Time base (sweep) generator - time base circuit uses a uni-junction transistor, which is used to produce the sweep. The saw tooth voltage produced by the time base circuit is required to deflect the beam in the horizontal section. The spot is deflected by the saw tooth voltage at a constant time dependent rate. Horizontal amplifier - the saw tooth voltage produced by the time base circuit is amplified by the horizontal amplifier before it is applied to horizontal deflection plates. Trigger circuit - the signals which are used to activate the trigger circuit are converted to trigger pulses for the precision sweep operation whose amplitude is uniform. Hence input signal and the sweep frequency can be synchronized. Power supply - the voltages required by CRT, horizontal amplifier, and vertical amplifier are provided by the power supply block. It is classified into two types - (1) negative high voltage supply (2) positive low voltage supply The voltage of negative high voltage supply is from -1000V to -1500V. The range of positive voltage supply is from 300V to 400V.
- 51. CRO MATRUSRI ENGINEERING COLLEGE Working of cathode ray oscilloscope: when the electron is injected through the electron gun, it passes through the control grid. The control grid controls the intensity of electron in the vacuum tube. If the control grid has high negative potential, then it allows only a few electrons to pass through it. Thus, the dim spot is produced on the lightning screen. If the negative potential on the control grid is low, then the bright spot is produced. Hence the intensity of light depends on the negative potential of the control grid. After moving the control grid the electron beam passing through the focusing and accelerating anodes. The accelerating anodes are at a high positive potential and hence they converge the beam at a point on the screen. After moving from the accelerating anode, the beam comes under the effect of the deflecting plates. When the deflecting plate is at zero potential, the beam produces a spot at the centre. If the voltage is applied to the vertical deflecting plate, the electron beam focuses at the upward and when the voltage is applied horizontally the spot of light will be deflected horizontally. Applications: used for display of waveforms, measurement of voltages, measurement of current, measurement of frequency and measurement of phase difference.
- 52. CRO MATRUSRI ENGINEERING COLLEGE Applications: used for display of waveforms, measurement of voltages, measurement of current, measurement of frequency and measurement of phase difference.
- 53. Problems MATRUSRI ENGINEERING COLLEGE 1.Determine the value of forward current in the case of a PN Junction diode, with Is=10µA and Vf=0.8V at T =300K, assume silicon diode.
- 54. Problems MATRUSRI ENGINEERING COLLEGE 2.The reverse saturation current of a silicon PN Junction diode is 10µA. Calculate the diode current for the forward bias voltage of 0.6V at 250C
- 55. Problems MATRUSRI ENGINEERING COLLEGE 3.A half-wave rectifier, having a resistive load of 1000Ω, rectifiers an alternating voltage of 325V peak value and the diode has a forward resistance of 100Ω. Calculate a) peak, average and rms value of current b)dc output power c) ac input power d) efficiency of the rectifier
- 56. Problems MATRUSRI ENGINEERING COLLEGE 4.A 230V, 60Hz voltage is applied to the primary of a 5:1, step-down, center – tap transformer used in a full-wave rectifier having a load of 900Ω . If the diode resistance and secondary coil resistance together has a resistance of 100Ω, determine a) dc voltage across the load b) dc current flowing through the load c) dc power delivered to the load d) PIV across each diode e) ripple voltage and its frequency f) rectification efficiency
- 57. 5. The diode current is 0.6mA when the applied voltage is 400mV, and 20mA when the applied voltage is 500mV. Determine η Assume KT/q=25mv MATRUSRI ENGINEERING COLLEGE Problems
- 58. Short Answer Questions MATRUSRI ENGINEERING COLLEGE
- 59. Long Answer Questions MATRUSRI ENGINEERING COLLEGE 1.Draw and explain the V-I characteristics of a PN junction diode under forward and reverse bias? Derive the total current equation of PN diode? 2.Draw the circuit diagram of a centre tapped full wave rectifier and explain its working. Also define and derive the expression for (i) ripple factor (ii) conversion efficiency (iii) TUF (iv) regulation. 3.Explain how does a zener diode behaves as voltage regulator? 4.A half wave rectifier circuit, having a resistive load of 1000Ω, rectifies an alternating voltage of 325V peak value and the diode has forward resistance of 100Ω. Calculate (i) peak (ii) average (iii) RMS value of current (iv) AC input power (v) DC output power (vi) efficiency. 5.What is hall effect? Derive an expression for hall coefficient. 6.By drawing energy band diagrams show how fermi levels are indicated in intrinsic and extrinsic materials in both n-type and p-type materials. 7.Explain capacitor filter with FWR with required waveforms and derive ripple factor equation. 8.A 230V, 50hz voltage is applied to the primary of a 5:1 step down centre tapped transformer in FWR having a load of 900Ω. Determine (i) DC voltage across the load (ii) idc (iii) DC power delivered to the load (iv) PIV across each diode.
- 60. Long Answer Questions MATRUSRI ENGINEERING COLLEGE 6.By drawing energy band diagrams show how fermi levels are indicated in intrinsic and extrinsic materials in both n-type and p-type materials. 7.Explain capacitor filter with FWR with required waveforms and derive ripple factor equation. 8.A 230V, 50hz voltage is applied to the primary of a 5:1 step down centre tapped transformer in FWR having a load of 900Ω. Determine (i) DC voltage across the load (ii) idc (iii) DC power delivered to the load (iv) PIV across each diode. 9.What is an ideal diode? How can it be represented as switch? Draw the equivalent circuit and its characteristics.
- 61. Questions & Answers MATRUSRI ENGINEERING COLLEGE