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Basic Electronic Lab Manual LAB EXPERIMENT # 02 Roll No: ______________ Grade: Signature: TO ANALYZE THE VOLTAGE-CURRENT CHARACTERISTICS OF DIODE Lab Objective: To learn how to connect a diode in forward and reverse Bias arrangement. To understand V-I Characteristic of diode. Required Equipment’s: 1. A compatible PC with Multisim installed in it. 2. Diode (any low signal model). 3. Multimeter. 4. DC Power Supply 0V – 12V. 5. Resistor 1k – 10k ohm. Introduction: Diode is a two terminal semiconductor device with an ability to conduct current only in one direction after a certain amount of voltage called barrier potential is applied to it in a proper way. Diode is one of great invention which is used in many applications such as rectifier circuits, voltage limiter circuits, voltage clamper circuits, voltage multiplier circuits etc. Diode biasing methods: There are three “biasing” condition for standard junction diode, are as follows: 1. Zero Bias: No external voltage is applied to PN junction. 2. Forward Bias: Diode is said to be forward biased; if positive terminal of diode is connected with positive of voltage source and negative terminal of diode is connected with negative of voltage source as shown in fig1 (a). Silicon diode will conduct current at 0.7V and germanium diode will conduct current at 0.3V when diode is forward biased, 0.7volt is called barrier potential for silicon diode and 0.3V is barrier potential for germanium diode. Before the value of voltage across diode reaches its barrier potential; there is very small amount of current that is flowing through diode. The current due to majority carrier is called forward current and current due to minority carrier is called reverse current. After the value of voltage across diode reached its barrier potential; there is a rapid change in the value of current through diode. The graphical representation of this phenomenon is as shown in below fig 2(b). 3. Reverse Bias: Diode is said to be reverse biased; if positive terminal of diode is connected with negative of voltage source and negative terminal of diode is connected with Basic Electronic Lab Manual positive of voltage source. Reverse bias is a condition that essentially prevents current through the diode. An ideal diode behaves as an open switch when reverse biased, the VI characteristic of ideal diode is shown in fig 2(a) whereas practically there is a very small amount of current (negligible) that is flowing through diode even if diode is reverse biased. The VI characteristic of forward and reverse bias diode is as shown below fig 2(b). Figure 1(a) Forward Bias Fig 2(a) VI Characteristic of an ideal diode Figure 1(b) Reverse Bias Fig 2(b) VI Characteristic of practical diode diode Procedure: 1. Make the circuit as shown in figure 1(a) connect positive terminal of a diode with positive of battery and connect negative terminal of a diode with negative of battery a current limiting 1k ohm resistor may also be added in series with diode. 2. Connect the ammeter in series and volt meter in parallel with diode. Basic Electronic Lab Manual 3. Now switch on the power supply and carefully turn the voltage control clock wise whilst watching the ammeter. 4. Set the value of voltage and observe the value of current. Plot these values on graph paper. 5. Make the circuit as shown in figure 1(b) connect positive terminal of a diode with negative of battery and connect negative terminal of a diode with positive of battery a current limiting 1k ohm resistor may also be added in series with diode, now repeat the same procedure from 2 to 4. Lab Questions: 1. What is barrier potential and write down the values of barrier potential for silicon diode and germanium diode? 2. How to make a diode forward biased with the help of battery (voltage source)? 3. What are the forward and reverse currents? 4. What is depletion region? Basic Electronic Lab Manual LAB EXPERIMENT # 03 Roll No: ______________ Grade: Signature: OPERATION AND ANALYSIS OF HALF WAVE RECTIFIER Objective: To understand the operation of half wave rectification. Equipment: 1. A compatible PC with Multisim installed in it. 2. Multimeter 3. Transformer (single input single output) 4. AC power supply 5. Oscilloscope 2 channel. 6. Diode. 7. Resistor 1k ohm. Introduction: A rectifier is a circuit that converts pulsating ac into pulsating dc. There are three basic types of rectifier circuits: the half wave rectifier, full wave rectifier, full wave (center tapped) and bridge rectifier, bridge rectifier is most commonly used. Half Wave Rectifier: Half wave rectifier is the process, which converts an ac sinusoidal input voltage into a pulsating dc voltage with the output pulse occurring for each input cycle. The half wave rectifier is made up of single diode and a resistor (load). The half wave rectifier conducts current only during positive half cycle of the ac input supply. The negative half cycle of the ac supply is suppressed. i.e. during negative half cycle, no current is conducted and hence no voltage appear across the load as shown in figure 3.1. Rectifiers are found in all dc power supplies that operate from an AC voltage source. Fig 3.1 half wave rectifier Basic Electronic Lab Manual Working Half Wave Rectifier: Figure 3.2 illustrates the operation of half wave rectification. When the sinusoidal input voltage Vp(in) goes positive, the diode is forward-biased and conducts current through the load resistor. The current produces an output voltage across the load R, which has the same shape as the positive half-cycle of the input voltage. Fig 3.2 Half wave rectifier operation During the positive half-cycle, the input voltage must overcome the barrier potential before the diode becomes forward-biased. This results in a half-wave output with a peak value that is 0.7 V less than the peak value of the input. The expression for the peak output voltage is as shown below; Vp(out) = Vp(in) - 0.7 V where Vrms = vp/2 while Vavg = vp/ π Note: Vp denotes the peak value of d.c rectified output Ripple Factor (r): Ripple factor is very important criteria for measuring the efficiencies of rectifier. Basically the variation in the output voltage due to charging and discharging is called ripple. Ripple factor is formally define as the ratio of rms value of ac component to the dc component in the output. Procedure: • Design a half wave rectifier circuit given to you in the Lab accordingly in which a diode is connected with secondary terminal of transformer has turn ratio 10:1 and connect ac signal with primary terminal of transformer. • Observe the rectified output signals. • Calculate the ripple factor and DC voltage using oscilloscope and compared it with measured voltage. Basic Electronic Lab Manual Lab Questions: 1. What is Half Wave and full wave rectification? 2. What is PIV (Peak Inverse Voltage)? 3. What is the common application for conversion of an AC voltage to DC? 4. What are the advantages and disadvantages of half wave rectifier? 5. Compare full wave and half wave rectifier? Basic Electronic Lab Manual LAB EXPERIMENT # 04 Roll No: ______________ Grade: Signature: Lab Objective: To understand the operation of Full wave rectification using bridge circuit. Required Equipment’s: 1. 2. 3. 4. 5. 6. A compatible PC with Multisim installed in it. Four Diodes (1N4001 – 1N4007) Multimeter AC voltage source Ordinary transformer Oscilloscope Discussion: Full wave bridge rectification is the process through which an ac sinusoidal input voltage is converted into a pulsating dc voltage with two output pulses occurring for each cycle. The full wave rectifier consist of four diodes and load resistors. Full Wave Bridge Rectifier: The bridge rectifier uses four diodes connected as shown in Fig 4-1a. When the input cycle is positive as in part (a), diodes D1 and D2 are forward-biased and conduct current in the direction shown. A voltage is developed across RL that looks like the positive half of the input cycle. During this time, diodes D3 and D4 are reverse-biased. Fig 4-1 Bridge Rectifier Basic Electronic Lab Manual When the input cycle is negative as shown in part (b), diodes D3 and D4 are forward biased and conduct current in the same direction through RL as during the positive half-cycle. During the negative half-cycle, D1 and D2 are reverse-biased. A full-wave rectified output voltage appears across RL as a result of this action. Two diodes are always in series with the load resistor during both the positive and negative half cycles. If these diode drops are taken into account, the output voltage is Vp(out) =Vp(sec) -1.4 V The below fig 4.2 shows the diode drops; Fig 4-2 The number of positive alternations that make up the full-wave rectified voltage is twice that of the half-wave voltage for the same time interval. The average value, which is the value measured on a dc voltmeter, for a full-wave rectified sinusoidal voltage is twice that of the half-wave, as shown in the following formula: Vavg=2Vp/π Whereas the AC voltmeter shows RMS value and that is given by Vrms=Vp/√2 Procedure: • • • Design a neat and clean circuit in Multisim as shown in figure 4-1with proper labeling for full wave bridge rectifier in Multisim, realize it on breadboard Calculate Vp(out),Vavg and Vrms with formulas described above and prove the results using Multimeter. Calculate the ripple factor in each case. Questions: 01: What type of rectifier has high ripple factor? 02: Write down a common application of full wave rectifier 03: Differentiate between full wave center tapped and bridge rectifier Basic Electronic Lab Manual LAB EXPERIMENT # 05 Roll No: _____________ Grade: Signature: FULL WAVE CENTRE-TAP TRANSFORMER RECTIFICATION Lab Objective: To understand the operation of Full wave rectification by centre-tap rectification. Required Equipment’s: 1. 2. 3. 4. 5. 6. A compatible PC with Multisim installed in it. Four Diodes (1N4001 – 1N4007) Multimeter AC voltage source Ordinary transformer Oscilloscope Full Wave Rectifier: Full wave rectification is the process through which an ac sinusoidal input voltage is converted into pulsating dc voltage with two output pulses occurring for each input cycle. The full wave rectifier consists of two diodes and load resistor (RL). The center tapped rectifier is a type of full wave rectifier that uses two diodes connected to the secondary of the center tapped transformer as shown in fig 3-2 Fig 3-2 center tapped rectifier Basic Electronic Lab Manual Center Tapped Transformer: The center tapped transformer is more or less same as the normal transformer. It differs only when an additional wire is connected across the exact middle point of the secondary winding of a transformer; it is called a center tapped transformer. The wire is adjusted such that it falls in the exact middle point of the secondary winding and is thus at zero volts, forming the neutral point for the winding. This is called the “center tap” and this thing allows the transformer to provide two separate output voltages which are equal in magnitude, but opposite in polarity to each other. Full Wave Rectifier Operation: During positive half cycle of input AC signal, diode D1 is forward biased and diode D2 is reverse biased as shown in fig 3-2. During negative half cycle input AC signal, diode D1 is reverse biased and diode D2 is forward biased as shown in fig 3-2, which means rectified output is obtained during both positive and negative half cycle of input AC, whereas amplitude of half wave center tapped rectified output voltage of center tapped rectifier is always one half of total secondary voltage less the diode drop, no matter what the turn’s ratio. Vp(out)=0.5Vp(sec)-0.7 The average output voltage of full wave rectifier is twice of that of half wave and it is given as Vavg = 2Vp(out)/π Vrms = Vp(out)/√2 Ripple Factor (r): Ripple factor is very important criteria for measuring the efficiencies of rectifier. Basically the variation in the output voltage due to charging and discharging is called ripple. Ripple factor is formally define as the ratio of rms value of ac component to the dc component in the output. Procedure: 1. Design the center tapped full wave rectifier circuit in Multisim as shown above in figure 32 and observes the waveform. 2. Observe the rectified output. 3. Calculate the ripple factor in each case. Basic Electronic Lab Manual LAB EXPERIMENT # 06 Roll No: _____________ Grade: Signature: Zener Diode Characteristics and Voltage Regulation Objective: Analyze the reverse characteristics of Zener diode. Understand voltage regulation provided by Zener. Components 1. 2. 3. 4. 5. 6. A PC compatible with Multisim. Multimeter Zener diode Surge resistor DC signal source Load resistor Discussion: Zener diode is one of the types of diode which was developed by scientist Zener Clarence. Zener diode is a heavily doped silicon PN junction device that is designed to operate in reverse breakdown region. In Zener diode two types of reverse breakdowns occur. i. Zener break down ii. Avalanche breakdown i. Zener breakdown: It occurs at low reverse voltage, Occurs only in Zener diode. ii. Avalanche breakdown: Occurs at sufficiently high reverse voltage such that diode will be damaged. Occurs in both rectifier and Zener diode. Due to heavy doping depletion region becomes thin and there are enough charge carriers (majority and minority) in P & N region, that’s why less voltage is required by Zener diode to operate in reverse breakdown region. When Zener diode reaches Zener break down voltage “Vz”, its voltage remains almost constant even though the current changes drastically as shown in the figure 6.1. In other words it can also be said that when Zener Basic Electronic Lab Manual diode is operating in Zener breakdown region, it acts as voltage regulator for specified range of reverse current. Zener diode has two states, on state and off state. ON STATE: When reverse voltage across a Zener diode is equal to or more than breakdown voltage Vz, the current increases very sharply. In this region, curve is most vertical. It means voltage across Zener diode is constant even though the current through I change under such condition. The Zener is said to be in “ON STATE”. OFF STATE: When reverse voltage across the Zener diode is less than Vz but greater than 0v, the Zener diode is said to be in off state, under such condition the Zener diode can be represented by open switch. Due to characteristic of voltage regulation, Zener diode equivalent circuit is consisting of a voltage source as shown in figure 6.2. Zener diode does not produce DC voltage, but constant voltage drop is represented by a constant DC voltage source Zener are available with breakdown voltages from 1.8 to 200 volt with tolerance from 1% to 20%. Figure 6.1: IV characteristic curve for Zener diode Figure 6.2: Schematic symbol of Zener diode and it equivalent circuit, (a) Ideal model (b) Practical model Basic Electronic Lab Manual Procedure: • • • Prepare a series circuit consisting of a resistor, Zener diode and DC voltage source as shown in figure 6.3. Take different readings of current through the load at different values of voltage across Zener diode. Observe that when input voltage is sufficiently increased then voltage across Zener diode remains constant even though current is changing w.r.t to input voltage. Figure 5-3: Zener diode as a voltage regulator Lab Questions: 01: What is voltage regulator? 02: Describe two types of reverse break downs that can occur in Zener diode. 04: What is the application of Zener diode in DC power supply? 05: what is difference between rectifier and Zener diode? Basic Electronic Lab Manual LAB EXPERIMENT # 07 Roll No: _____________ Grade: Signature: Filters and Construction of DC Power Source Lab Objective: • Analyze the behavior of filters and need in power supply. • Simple construction of DC power supply with regulation. Equipment’s: A Compatible PC with Multisim Oscilloscope (4 channel) FWB rectifier Load and Surge resistors Transformer step-down Electrolytic capacitor Light Emitting diode (LED) Discussion: The power supply of an electronic system is used to convert the ac energy into dc energy. The basic power supply can be broken into four circuit groups as shown in figure 7` AC DC Transformer Rectifier Filter Regulator Figure 6-1 block diagram of Regulated D.C power supply Transformer: In general, the ac line voltage present in your house wiring is not suitable for electronic circuits. Most circuits require a considerably lower voltage, while a few require higher voltage. The transformer serves to convert the ac line voltage to a voltage level more appropriate to the needs of the circuit to be powered (step down the 220 V ac into the desired level of ac voltage normally 12v or 15 b). However, a line transformer is generally large and heavy, and is rather expensive. Therefore, some power supplies (notably for PCs) are deliberately designed to operate directly from the ac line without a line transformer. The output of the transformer is still an ac voltage, but now of an appropriate magnitude for the circuit to be powered. Basic Electronic Lab Manual Rectifier: The next step is to force current to flow in one direction only, preventing the alternations that occur in the transformer and the ac line. This process is known as rectification, and the circuit that accomplishes the task is the rectifier. There are many different rectifier configurations that may be used according to the requirements of the circuit. The output of the rectifiers a pulsating dc, which still has some of the variations from the ac line and transformer. To observe better performer, bridge rectifier is used. The principle advantage of a bridge rectifier is you do not need a center tape on the secondary of the transformer. A further but significant advantage is that the ripple frequency at the output is twice the line frequency (i.e 50Hz or 60Hz) and makes filtering somewhat easier. Filter: The pulsating dc form the rectifier is generally still not suitable to power the actual load circuit. The pulsating typically vary from 0V to the peak output voltage of the transformer. Therefore, insert a circuit to store energy during each voltage peak, and then leaves it to the load when the rectifier output voltage drops. This circuit is called a filter, and its job is to reduce the pulses from the rectifier to a much smaller ripple voltage. No filter configuration can be absolutely perfect, but a properly designed filter will provide a dc output voltage with only a small ac ripple. Capacitor is use for reducing the variations in the rectifier output signal. In power supply we must consider surge currents. Initially, when we turn the power supply on, the filter capacitor is fully discharged and acts as a short circuit. So initially only the resistance of the diode and the winding resistance of the transformer secondary limit the diode current. Therefore a surge resistor is an added before capacitor to add some charging time constant. The discharge time depends on the load resistance. Regulator/Zener Diode: The final circuit in the basic power supply is the voltage regulator. In this case we use zener diodes as voltage regulators, as they are capable of maintaining a constant load voltage despite changes in the rectifier output voltage. Procedure: 1. Make the connection as shown in figure 2. Use the digital multimeter to measure the voltages and currents at different points. Basic Electronic Lab Manual Lab Questions: 1. 2. 3. 4. What is DC power supply? What are the basic building blocks of a dc power supply? Why do we add surge resistor? What is the purpose of load resistor if there is LED at the output? Basic Electronic Lab Manual LAB EXPERIMENT # 08 Roll No: _____________ Grade: Signature: APPLICATION OF DIODES IN WAVEFORM SHAPING Lab Objective: Understand that how a diode can clip/limit the signal. Learn that how a diode can clamp the signal. Equipment’s: 1. 2. 3. 4. 5. 6. A PC with Compatible Multisim Resistors Diodes DC and AC voltage source Oscilloscope Multimeter 7. Capacitor Discussion: Diode limiter circuits are usually used to limit the +ve and/or –ve input signal. Positive diode limiter circuit is shown in figure 7.1(a) and negative diode limiter circuit is shown in figure 7.1(b). When positive input half cycle of voltage signal is applied to circuit as shown in figure 7.1(a); diode will be forward biased and it can drop only 0.7volt and remaining input voltage will be dropped across R1. When negative input half cycle of voltage signal is applied to circuit as shown in figure 7.1(a); diode will be reverse biased and it will appear as open switch, so input voltage will be dropped across series combination of R1 and RL. When negative input half cycle of voltage signal is applied to circuit as shown in figure7.1 (b); diode will be forward biased and it can drop only 0.7volt and remaining input voltage will be Basic Electronic Lab Manual dropped across R1. When positive input half cycle of voltage signal is applied to circuit as shown in figure 7.1(b); diode will be reverse biased and it will appear as open switch, so input voltage will be dropped across series combination of R1 and RL. Figure 01: Diode limiter circuit. (a) Positive limiter (b) Negative limiter Diode Clamper Circuit: Diode clamper circuits also known as DC restorer circuits are usually used to add DC level to an AC signal. Positive diode clamper circuit is shown in figure 7.2 and negative diode clamper circuit is shown in figure 7.3. Positive diode clamper circuit inserts a positive DC level in the output waveform. When negative half cycle of input AC signal is provided to positive diode clamper circuit, diode is forward biased and capacitor will be charged up to voltage level (Vin-0.7), because diode has to drop 0.7 volts. During when positive half cycle of input AC signal is provided to positive diode clamper circuit, diode is reverse biased and as capacitor is already charged up to voltage level (Vin-0.7) volts, now this capacitor will work as a battery of (Vin-0.7) volts, that’s why capacitor voltage is added with positive half cycle of AC input signal, furthermore this capacitor voltage will also be added with next negative half cycle of input AC signal. In result input AC signal is shifted upward by the magnitude of (Vin-0.7) volts. Figure 7.2: Positive diode clamper circuit Basic Electronic Lab Manual Negative diode clamper circuit inserts a negative DC level in the output waveform. When positive half cycle of input AC signal is provided to negative diode clamper circuit, diode is forward biased and capacitor will be charged up to voltage level (Vin-0.7), because diode has to drop 0.7volts. During when negative half cycle of input AC signal is provided to negative diode clamper circuit, diode is reverse biased and as capacitor is already charged up to voltage level (Vin-0.7)volts, now this capacitor will work as a battery of (-Vin+0.7)volts, that’s why capacitor voltage is added with negative half cycle of AC input signal, furthermore this capacitor voltage will also be added with next positive half cycle of input AC signal. In result input AC signal is shifted downward by the magnitude of (Vin-0.7) volts. Figure 7.3: Negative diode clamper circuit Input and output signal waveforms are also shown in figure 01 and 02. For good clamping action, a clamper circuit requires a capacitor with RC time constant at least 10 times the period of input signal. Procedure: Design a circuit according to schematic diagram shown in figure 7.1, 7.2 and 7.3. Observe the input and output signal waveforms on oscilloscope. Lab Questions: 1. 2. 3. 4. What is diode Clipper and Clamper circuits? What is difference between positive and negative diode clipper circuit? What is difference between positive and negative diode clamper circuit? What is biased Clipper and Clamper circuits? Basic Electronic Lab Manual LAB EXPERIMENT # 09 Roll No: _____________ Grade: Signature: IDENTIFICATION AND CHARACTERISTICS OF TRANSISTORS Lab Objective: Identify the terminals and type of transistors. Read out transistors parameters using datasheets. Switching characteristics of transistors. Required Equipment’s: 1. 2. 3. 4. Transistors. Multimeter. Data Sheet. Breadboard. Discussion: In the analog world of continuously varying signals, a transistor is a device used to amplify its electrical input. In the digital world, a transistor is a binary switch and the fundamental building block of computer circuitry. Like a light switch on the wall, the transistor either prevents or allows current to flow through. The transistor was invented by three scientists at the Bell Laboratories in 1947, and it rapidly replaced the vacuum tube as an electronic signal regulator. A transistor regulates current or voltage flow and acts as a switch or gate for electronic signals. A transistor consists of three layers of a semiconductor material, each capable of carrying a current. There are two types of transistors 1. Bipolar Junction Transistor (BJT) 2. Field Effect Transistor (FET) Bipolar Junction Transistors: BJT is semiconductor device; it is constructed of three doped semiconductor materials. Either n-type material is sandwiched between two p-type materials or p-type material is sandwiched between two n-type materials and these three materials make three regions of transistor as shown in figure 01. Three regions of transistor are known as Base (B), Collector (C), Emitter (E), these regions separated by two pn-junctions known as base-emitter and base-collector junction. A wire lead is connected to each of three regions, and these leads are labeled as E, B, and C for emitter, Base, Collector respectively. Emitter is heavily doped, Base is lightly doped, and Collector is moderately doped. Physically collector is bigger than emitter and base, because collector has to Basic Electronic Lab Manual dissipate more power. Transistors are usually used as amplifiers and switches. Schematic symbol of transistor is shown in figure 02. Figure 01: Structure of npn (on left side) and pnp (on right side) transistor Figure 02: Schematic symbol of transistor (a) npn (b) pnp Transistor Terminal Identification Transistor terminals can be identified with any of following methods: 1. Ohm meter 2. Diode option on digital multimeter 3. Case identification 1. Using Ohm (Ω) Meter In transistor there are two PN-Junctions, when ohm meter is connected with any of two leads and if that junction of transistor is forward biased then it will show some Basic Electronic Lab Manual value of resistance else it will show “OUT of Range”. So find out both junctions with the help of ohm meter, such that both junctions are forward biased. Now check if common terminal of transistor is connected with positive probe of ohm meter; transistor is said to be NPN else PNP. This common terminal is base. Junction with slightly higher resistance is base emitter, so emitter terminal is also identified. Junction with slightly lower resistance is base collector, so collector terminal is also identified. RBE>RBC very minor difference (forward resistance is round about in the range of kilo ohms) 2. Using Diode Option in Meter. First identify common terminal and type of transistor such as npn or pnp. Then junction with slightly higher forward voltage drop is base emitter and junction with slightly lower forward voltage drop is base collector. All three terminals are identified. VBE>VBC very minor difference (forward voltage drop is round about 0.7 volt) 3. Through Case Structure Identification: Transistor terminal identification with the help of case is very easy as shown in figure 03. But care must be taken, because same case may have different terminal configuration by different manufacturers. Figure 03: Transistor terminal identification with the help of its case output Characteristics of BJT: When dealing with transistor configurations, characteristics curves are very important because they can predict the performance of a transistor. There are three curves, an input characteristic curve, a transfer characteristic curve and output characteristic curve. Of these curves, the most useful for predicting the transistor performance is the output characteristic curve. Output characteristic curves of BJT are displaying the output voltages and currents for different input currents. It simply provides the V-I relationship at the output terminals, with either the input current or input voltage as parameters. For each transistor configuration, CE, CC and CB, the input curves are slightly different. Basic Electronic Lab Manual Common Emitter Output Characteristic Curves. In common emitter configuration, the input is applied between base and emitter and output is taken from the collector and emitter as shown in figure 9-2. In CE input current is Ib and output current Ic. Figure 9.2 Common Emitter Configuration (a) NPN (b) PNP In order to determines the output characteristic of CE configuration Ib is maintained constant at several convenient levels. At each fixed level of base current (Ib), collector emitter voltage (Vce) is adjusted in step and corresponding values of collector current (Ic) are recorded. Then for each level of Ib , Ic is plotted v/s Vce. At typical output characteristic for a BJT in CE mode shown in figure 9.3 Figure 9.3 output characteristics of BJT in CE mode Basic Electronic Lab Manual PROCEDURE: 1. 2. 3. 4. 5. Make the connections according to the figure 9.4. Rotate both variable control to minimum. Switch ON the power supply Set 10 k() to give a base current of 2.5 () Starting from 0.5V vary Vce to according to table and note down the corresponding values of Ic. 6. Take similar reading with different reading values of Ib. 7. Fill the following table and plot the graph representing the output characteristic of NPN transistor for CE mode. Figure 9-4: BJT Common Emitter Configuration Circuit Keeping the base current Ib fixed at some values say (2.5µA) and varies the values Vce say some values (0.5V) and cheeks increase or decrease within the current on ammeter. after checking the current increase (0.8mA) then plot reading on graph paper, taking Ic along y-axis and Vce along x-axis this gives the output characteristics at (Ib=2.5µA). Lab Questions: 1. How many regions of operation does BJT have? 2. How to identify transistor terminals? 3. What are the applications of transistor? 4. Draw schematic symbol for pnp and npn transistor. Basic Electronic Lab Manual LAB EXPERIMENT # 10 Roll No: _____________ Grade: Signature: BIASING, SWITCHING AND AMPLICATION OF TRANSISTORS Objective: Learn that how a transistor can operate as amplifier. Learn that how a transistor can operate as a switch. Equipment’s: 1. PC compatible with Multisim 2. Transistor BC547/2N3004 3. DC and AC Power Source 4. Multimeter 5. Resistors Theory: BJT is semiconductor device; it is constructed of three doped semiconductor materials. Either n-type material is sandwiched between two p-type materials or p-type material is sandwiched between two n-type materials and these three materials make three regions of transistor. Three regions of transistor are known as Base (B), Collector (C), Emitter (E), these regions separated by two pn-junctions known as base-emitter and base-collector junction. A wire lead is connected to each of three regions, and these leads are labeled as E,B,C for emitter, Base, Collector respectively. Emitter is heavily doped, Base is lightly doped, and Collector is moderately doped. Physically collector is bigger than emitter and base, because collector has to dissipate more power. Transistors are usually used as amplifiers and switches. Transistor as a Switch The majority application of transistor is that it can be utilize for switching operation when it’s used as a electronic switch, in this condition a switch normally operates alternatively in cutoff and saturation. Transistor can be operated in one of three following configurations, when common terminal is grounded. 1. Common Base Configuration 2. Common Emitter Configuration 3. Common Collector Configuration Basic Electronic Lab Manual Transistor can be operated in following regions Cutoff region (Both junction BE and BC are reversed biased) Active Region (BE junction is forward biased and BC junction is revere biased) Saturation Region (Both junction BE and BC are forward biased) Breakdown region (Transistor currents and/or voltages exceed than maximum specified values in data. Transistor should not be operated in this region, because it will be damaged) Transistor works as an open switch in any of the following conditions IB=0v, IC =0v VCE ( cutoff ) =VCC Both junctions of transistor are reversed biased Transistor works in its cut off region Transistor works as a close switch in any of the following conditions I C=IC ( Sat ) VCE=VCE ( Sat ) Both junctions of transistor are forward biased Transistor works in its saturation region Transistor as an open switch and close switch is shown in figure 10.1 Figure 10.1: Switching action of Ideal Transistor Transistor as an Amplifier: Amplification is the process of linearly increasing the amplitude of an electrical signal. Transistor amplifier circuit, input and output voltage signal waveforms are shown in figure 02. Where input AC signal is superimposed on VBB, which causes IB to change. Smaller change in IB causes higher change in IC. Using equation (VCC = I CRC+VCE), it can be noticed that Increase in IC causes Basic Electronic Lab Manual decrease in VCE vice versa. That is why both input and out voltage signal waveforms are 180 degree out of phase. Figure 10.2: Transistor as an amplifier in common emitter configuration Voltage gain is the ratio of Vc / Vb Procedure:- Prepare following circuit as shown in figure 10.1 and figure 10.2. Depending upon the transistor model, set the values of RC, RB, VCC and Vin such that transistor should be operated in its saturation and then cutoff regions continuously. Observation:- It is observed that when transistor is in its saturation region, LED is turning on for one second and when transistor is in its cutoff region, LED is turning off. From figure observe the magnitude of output signal is grater then input signal. Lab Questions 1. Draw and discus the transistor switching circuit and what are the values of RC, Rb, VCC and Vin that you have considered during this practical? 2. What is amplification? Draw the circuit diagram for a transistor amplifier circuit with values of different components and energy sources that is observed during practical.