Introduction to electronics and communicatiosn

electronics and communicatiosn

1. Module -1 A . Electronic Circuits Power Supplies: Block diagram, Rectifiers, Reservoir and smoothing circuits, Full-wave rectifiers, Bi-phase rectifier circuits, Bridge rectifier circuits, Voltage regulators, Output resistance and voltage regulation, Voltage multipliers . B.Amplifiers Types of amplifiers, Gain, Input and output resistance, Frequency response, Band-width, Phase shift, Negative feedback, multi-stage amplifiers (Text 1) 2

2. ELECTRICAL FUNDAMENTALS Fundamental units You will already know that the units that we now use to describe such things as length, mass and time are standardized within the International System of Units. SI system is based upon the seven fundamental units Quantity Unit Abbreviation Current ampere A Length meter m Luminous intensity candela cd Mass kilogram kg Temperature Kelvin K Time second s Matter mol mol

3. FOLLOWING TABLE SHOWS DIFFERENT ELECTRICAL QUANTITIES WITH UNITS

4. Electronics Electronics is a branch of Physics that deals with the theory and use of devices in which the electrons travel through a vacuum, gas, or a semiconductor medium. The motion of electrons takes place under the influence of applied electric and/or magnetic fields . OR Devices that use electricity and electrical components to perform a task — like stereos, TVs, computers, and calculators etc . OR Electronics is a branch of physics that deals with the emission, behavior, and effects of electrons (as in electron tubes and transistors) and with electronic devices. 

5. COMMUNICATION Electronic communication is any form of communication that's broadcast, transmitted, stored or viewed using electronic media, such as computers, phones, email and video. The communication system is a system which describes the information exchange between two points. The process of transmission and reception of information is called communication. The process of communication refers to the transmission or passage of information or message from the sender through a selected channel to the receiver overcoming barriers that affect its pace. The process of communication is a cyclic one as it begins with the sender and ends with the sender in the form of feedback.

6. Electronics & Communication Engineering Electronics & Communication Engineering deals with the electronic devices, circuits, communication equipments like transmitter, receiver, integrated circuits (IC). It also deals with basic electronics, analog and digital transmission & reception of data, voice and video (Example AM, FM,), microprocessors, satellite communication, microwave engineering, antennae and wave progression. It aims to deepen the knowledge and skills of the students on the basic concepts and theories that will equip them in their professional work involving analysis, systems implementation, operation, production, and maintenance of the various applications in the field of Electronics and Communications Engineering.

7. A.POWER SUPPLY Power supply is a device that supplies electric power to a load. The requirement for a reliable source of constant voltage in virtually all electronics systems has led to many advances in power supply design . Block diagram of DC power supply is as shown in figure.

8. BLOCK DIAGRAM OF DC POWER SUPPLY STEP-DOWN TRANSFORMER RECTIFIER RESERVOIR/ SMOOTHING FILTER VOLTAGE REGULATOR High Voltage AC Low Voltage AC Unsmoothed DC Smoothed DC Regulated DC

9. Step-Down Transformer – Steps down the AC main voltage which is usually high (220V) to a lower value (9V, 12V, 15V, 20V, 30V). This is achieved by varying the turns ratio on the transformer. Rectifier – The AC output from transformer secondary is then rectified using conventional silicon rectifier diodes to produce an unsmoothed output (pulsating DC). Reservoir/Filtering Circuit – The unsmoothed output from rectifier is smoothened by reservoir/filtering circuit (a high value capacitor). The high value capacitor stores a considerable charge. The capacitor helps smooth out the voltage pulses produced by the rectifier. Voltage Regulator – A series transistor regulator using a Zener diode as a fixed voltage source stabilizes and provides a constant voltage. Power supply with principle components 10

10. A SIMPLE DC SUPPLY 11

11. RECTIFIERS A rectifier is a device that converts alternating current (ac) to direct current (dc). RECTIFIERS HALF WAVE RECTIFIERS FULL WAVE RECTIFIERS BI-PHASE RECTIFIERS BRIDGE RECTIFIERS

12. HALF WAVE RECTIFIER A half-wave rectifier  converts an AC signal to DC by passing either the negative or positive half-cycle of the waveform and blocking the other. Half-wave rectifiers can be easily constructed using only one diode, but are less efficient than full-wave rectifiers. OR The simplest form of rectifier circuit makes use of a single diode and, since it operates on only either positive or negative half-cycles of the supply, it is known as a half-wave rectifier. Alternating Voltage Pulsating DC Voltage

13. OPERATION OF HALF WAVE RECTIFIER Semiconductor diodes are commonly used to convert Alternating Current (AC) to Direct Current (DC), also referred as Rectifiers. The simplest form of rectifier circuit uses a single diode and operates only in positive or negative half cycles of the supply, known as half-wave rectifier. The mains voltage (220 to 240V) applied to primary of step-down transformer. 14

14. The secondary of transformer steps down the 240V rms to 12V rms (the turns ratio 20:1). Diode D1 will allow the current to flow in the direction is shown below . The Diode D1 will be forward biased during each positive half-cycle and behaves as a closed switch as shown in fig (a). When the circuit current flows in opposite direction, the voltage bias across the diode will be reversed, causing the diode to be reverse biased and act like an open switch as shown in fig (b). 15

15. T1 RL D1 Vin t + - VL t FWD Biased + - Current Flow + - A B

16. T1 RL D1 Vin t + - VL t REV Biased + - A B

17. WAVEFORMS OF HALF WAVE RECTIFIER Vin t VL t D1 FWD Biased D1 REV Biased D1 FWD Biased D1 REV Biased Pulsating Output Voltage

18. The switching action of D1 results in a pulsating output voltage developed across the load RL. Since the mains supply is at 50Hz, the pulses of the voltage developed across RL will also be at 50Hz. During the positive half-cycle, the diode will drop the 0.6 to 0.7V forward threshold voltage normally associated with silicon diodes. 19

19. However, during the negative half-cycle the peak ac voltage will be dropped across D1 when it is reverse biased . Assuming that the secondary of T1 provides 12V rms, the peak voltage output from transformer’s secondary winding will be given by Vpeak = 1.414 x Vrms = 1.414 x 12V = 16.97V 20

20. The peak voltage applied to D1 will be approximately 17V. The negative half cycles are blocked by D1 and thus only positive half cycles appear across R L . The actual peak voltage across R L will be 17V supplied from secondary of transformer minus the 0.7V forward threshold voltage. Therefore 16.3V will appear across R L .

21. Problem 1 A mains transformer having a turns ratio of 44:1 is connected to a 220 V r.m.s. mains supply. If the secondary output is applied to a half-wave rectifier, determine the peak voltage that will appear across a load. The r.m.s. secondary voltage will be given by: The peak voltage developed after rectification will be given by: Assuming that the diode is a silicon device with a forward voltage drop of 0.6 V, the actual peak voltage dropped across the load will be:

22. HALF WAVE RECTIFIER WITH A RESERVOIR CAPACITOR Half wave Rectifier with Reservoir Capacitor Voltage waveforms at various points in Half-wave Rectifier 23

23. HALF WAVE RECTIFIER WITH SMOOTHING CIRCUIT Smoothing Circuit This circuit employs two additional components, which act as a filter to remove the ripple. The value of additional capacitor is chosen so that the component exhibits a negligible reactance at the ripple frequency. LC Smoothing Circuit At ripple frequency, L exhibits high inductive reactance while C exhibits a low value of capacitive reactance. The combined effect reduces the amplitude of ripple, while having negligible effect on the direct voltage RC Smoothing Circuit LC Smoothing Circuit 24  

24. FULL WAVE RECTIFIERS Unfortunately, the half-wave rectifier circuit is relatively inefficient as conduction takes place only on alternate half-cycles. A better rectifier arrangement would make use of both positive and negative half-cycles. Full-wave rectifier circuits offer a considerable improvement over their half-wave counterparts. They are not only more efficient but are significantly less demanding in terms of the reservoir and smoothing components. A full wave rectifier is defined as a rectifier that converts the complete cycle of alternating current into pulsating DC, full wave rectifiers utilize the full cycle. There are two basic forms of full wave rectifier; 1.The bi-phase type and 2.The bridge rectifier type.

25. BI-PHASE FULL WAVE RECTIFIERS 26

26. OPERATION OF BI-PHASE RECTIFIER On the positive half-cycles, point A will be positive with respect to point B. Similarly, on the negative half cycle point B will be positive with respect to point C. In this condition D1 will allow conduction (its anode will be positive with respect to its cathode), while D2 will not allow conduction (its anode will be negative with respect to its cathode). Thus, D1 alone conducts on positive half-cycles. 27

27. OPERATION OF BI-PHASE RECTIFIER On negative half-cycles, point C will be positive with respect to point B. Similarly, point B will be positive with respect to point A. In this condition D2 will allow conduction (its anode will be positive with respect to its cathode). Thus, D2 alone conducts on negative half-cycles. The result is that current is routed through the load in the same direction on successive half-cycles. Furthermore, this current is derived alternately from the two secondary windings.

28. OPERATION OF BI-PHASE RECTIFIER T1 A D1 + - VL FWD Biased + - B C D2 RL Vin t REV Biased + -

29. OPERATION OF BI-PHASE RECTIFIER T1 A D1 + - vout REV Biased + - B C D2 RL vin t FWD Biased + -

30. WAVEFORMS OF BI-PHASE RECTIFIER Vin t VL t D1 FWD D2 FWD Pulsating Output Voltage D2 REV D1 REV D1 FWD D2 REV D2 FWD D1 REV

31. OPERATION OF BI-PHASE RECTIFIER As with the half-wave rectifier, the switching action of the two diodes results in a pulsating output voltage being developed across the load resistor (RL). However, unlike the half-wave circuit the pulses of voltage developed across RL will occur at a frequency of 100Hz (not 50Hz). This doubling of ripple frequency allows us to use smaller values of reservoir and smoothing capacitor to obtain the same degree of ripple reduction (reactance of a capacitor is reduced as frequency increases). As before, the peak voltage produced by each of the secondary windings will be approximately 17V and the peak voltage across RL will be 16.3V (i.e., 17V-0.7V forward threshold voltage dropped by the diodes) 32

32. BI-PHASE FWR WITH RESERVOIR CIRCUIT Th e reservoir capacitor C1 can be connected to ensure that the output voltage remains at or near the peak voltage even when the diodes are not conducting. The capacitor charges to peak value of 16.3V in the positive cycle and holds the voltage at this level when the diodes are non-conducting. The time required by C1 to charge to the maximum (peak) level is determined by the charging circuit time constant (the series resistance multiplied by capacitance value). 33

33. The series resistance in this circuit is the secondary winding resistance and forward resistance of the diode and minimal resistance of wiring and the connections. Hence C1 charges very rapidly as soon as either D1 or D2 starts to conduct. The time required for C1 to discharge is in contrast, very much larger. The discharge time is equal to product of the capacitance value and RL. In practice, RL is very large and greater than secondary winding, hence capacitor takes longer to discharge. During this stage D1 and D2 will be reverse biased and held in non-conducting state. As a consequence, the only discharge path for C1 is through RL. BI-PHASE FWR WITH RESERVOIR CIRCUIT

34. VOLTAGE WAVEFORMS FOR FULL WAVE RECTIFIER 35

35. BRIDGE RECTIFIER An alternative to the use of the bi-phase circuit is that of using a four-diode bridge rectifier in which opposite pairs of diode conduct on alternate half-cycles. This arrangement avoids the need to have two separate secondary windings.

36. BRIDGE RECTIFIER 37

37. OPERATION OF BRIDGE RECTIFIER T1 RL vin t vout D1 D2 D3 D4 A B + - - + FWD FWD REV REV t - +

38. OPERATION OF BRIDGE RECTIFIER T1 RL vin t vout D1 D2 D3 D4 - A B + FWD FWD REV REV + - t

39. OPERATION OF BRIDGE RECTIFIER Avoids 2 separate secondary windings 240V Main voltage is applied to primary of the step-down transformer (T1). The secondary winding provides 12Vrms of 20:1 On positive half cycles, point A will be positive with respect to B. D1 and D2 will conduct and D3 and D4 will not conduct On negative half cycles, point B will be positive with respect to A, D3 and D4 will conduct and D1 and D2 will not conduct. The current is routed through the load in the same direction on successive half cycles. Similar to bi-phase rectifier, the switching action of the two diodes results in a pulsating output voltage being developed across (RL) The peak voltage is approximately 16.3V ( i.e 17V less the 0.7V forward threshold voltage) 40

40. BRIDGE RECTIFIER WITH RESERVOIR CAPACITOR

41. VOLTAGE REGULATOR A voltage regulator provides a constant DC output voltage that is independent of AC line voltage variations, load current and temperature. The input to a voltage regulator comes from the filtered output of a rectifier derived from an AC voltage.

42. VOLTAGE REGULATOR Rs limits the Zener current to safe limit The source current is divided as Iz (current through Zener) and IL (current through RL) It is usual to allow 2-5mA to ensure Zener diode conducts The output voltage is equal to Zener breakdown voltage. 43

43. The ratio of Rs to RL is significant as the input voltage is voltage divided by them and made available as Vz Where V IN is unregulated input voltage The maximum value of Rs can be calculated from     The power dissipated in the Zener diode will be given as Pz = Iz * Vz . The minimum value for Rs is determined from off-load condition – max is the maximum rated power dissipation for the Zener diode.   44 VOLTAGE REGULATOR

44. OUTPUT RESISTANCE AND VOLTAGE REGULATION The internal resistance appears at the output of the supply and defined as change in output voltage to change in output current The regulation is given as 45

45. Example The following data was obtained during a test carried out on a d.c . power supply: ( i ) Load test Output voltage (no-load) = 12 V Output voltage (2 A load current) = 11.5 V (ii) Regulation test Output voltage (mains input, 220 V) = 12 V Output voltage (mains input, 200 V) = 11.9 V Determine (a) the equivalent output resistance of the power supply and (b) the regulation of the power supply.

46. PRACTICAL POWER SUPPLY CIRCUITS Figure shows a simple power supply circuit capable of delivering an output current of up to 250 mA. The circuit uses a full-wave bridge rectifier arrangement (D1 to D4) and a simple C–R filter. The output voltage is regulated by the shunt connected 12 V zener diode.

47. VOLTAGE MULTIPLIERS A. VOLTAGE DOUBLER Voltage doubler 49 By adding a second diode and capacitor, the output of half wave rectifier is increased. C1 will charge to positive peak of secondary and C2 will charge to negative peak of secondary voltage. Since the output is taken from C1 and C2 connected in series the resulting output voltage is twice that produced by one diode alone.

48. OPERATION OF VOLTAGE DOUBLER T1 RL D1 vin t FWD Biased + - + - + - C1 C2 D2 REV Biased Vp

49. OPERATION OF VOLTAGE DOUBLER T1 RL D1 vin t FWD Biased + - + - + - C1 C2 D2 REV Biased Vp + - Vp

50. B.VOLTAGE TRIPLER 52 C1 charges to positive peak secondary voltage, while C2 and C3 charges to twice the positive peak secondary voltage. The result is that the output voltage is the sum of the voltages across C1 and C3 which is 3 times the voltage that would be produced by a single diode. The ladder arrangement can be easily extended to provide even higher voltages but the efficiency of the circuit becomes increasingly impaired and high order voltage multipliers of this type are only suitable for providing relatively small currents.

51. Vm-Vm+Vc3-2Vm = 0

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