Module 7 Power Supply Circuits in Instrumentation PDF

Associate Diploma Program In Instrument Unit 7 POWER SUPPLY CIRCUITS IN INSTRUMENTATION Page 1 of 85  TABLE OF CONTENTS UNIT 7 - POWER SUPPLY CIRCUITS IN INSTRUMENTATION Enabling...

Associate Diploma Program In Instrument Unit 7 POWER SUPPLY CIRCUITS IN INSTRUMENTATION Page 1 of 85  TABLE OF CONTENTS UNIT 7 - POWER SUPPLY CIRCUITS IN INSTRUMENTATION Enabling Objectives Module 7.1 - Identify& Troubleshoot Power TERMINAL OBJECTIVE: Electronic circuits. The trainee will be given Module 7.2 - Identify, Construct & access to schematic Troubleshoot Op-Amps Circuits. diagrams of PSU, Op-Amps Filter, Oscillator Circuits and test equipments, from which Module 7.3 - Identify & Troubleshoot he will correctly identify and different types of Filter Circuits. troubleshoot the given circuits. All faults must be Module 7.4 – Identify, Construct & located and the proper Troubleshoot different types of Oscillator corrective actions described. Circuits. Introduction In this module, you will troubleshoot Rectifier, PSU, Amplifier PSU, Filter and Oscillator Circuits. You must complete the Systematic Troubleshooting Record (STR) when troubleshooting, recording your steps and procedures used to locate and correct a fault. The STR gives the instructor an indication of your understanding of the circuit operation, troubleshooting skills, and corrective action. Page 2 of 85 INSTRUMENT FITTER Module 7.1 IDENTIFY& TROUBLESHOOT POWER ELECTRONIC CIRCUITS. Page 3 of 85  INFORMATION SHEET Objective 7.1.1– Identify electronics components/circuits and troubleshoot them. Diode symbol Physical look of a diode Function Diodes allow electricity to flow in only one direction, only when the Anode end is made positive. The arrow of the circuit symbol shows the direction in which the current can flow. Types of diodes There are basically two types of semiconductor diodes, Germanium (Ge) and Silicon (Si). Page 4 of 85  INFORMATION SHEET Construction of a Diode: There are two types of semiconductor diodes: Silicon (Si) & Germanium (Ge) For Silicon the potential barrier voltage is in the order of 0.7v For Germanium the potential barrier voltage is in the order of 0.3v Hence: Silicon (Si) conducts/ operates at approximately 0.7v Germanium (Ge) conducts/ operates at approximately 0.3v Diode Characteristics Page 5 of 85  INFORMATION SHEET Structure of PN junction diode When placed in a simple battery-lamp circuit, the diode will either allow or prevent current through the lamp, depending on the polarity of the applied voltage. (Figure below) Page 6 of 85  INFORMATION SHEET Diode operation In Figure (a) the positive (+) of the supply is connected to the positive of the diode (anode) allowing Current to flow switching the bulb ON. In Figure (b) the negative (-) of the supply is connected to the positive of the diode (anode) blocking the Current switching the bulb OFF. Page 7 of 85  INFORMATION SHEET Diode Task 1 a. Which bulb lights up? _________________ b. Why: (Explain to your instructor) How to Test / Troubleshoot diode Good Diode Page 8 of 85  INFORMATION SHEET How to Test / Troubleshoot diode Faulty Diode Diode Task 2 Instructor to provide to the trainees with good and faulty diodes a. Test and fill the table below. b. What type of diode being used? (Germanium or Silicon) Page 9 of 85  INFORMATION SHEET c. From your testing select your outcome. Diode Task 3 a. Connect circuit (a) b. Test and fill the table below Forward biased connection Voltage Across the Diode Voltage Across the Bulb What type of diode being used c. Connect circuit (b) Page 10 of 85  INFORMATION SHEET d. Test and fill the table below Forward biased connection Voltage Across the Diode Voltage Across the Bulb What type of diode being used Application We will be looking at its application later on in the rectification section of the power supply. Capacitor & capacitance A capacitor is a device capable of storing electrical charge, made of two parallel plates separated by an insulator called “dielectric”, which could be air. The amount of charge that a capacitor can store and the length of time this charge can be held are dependent on its construction. Unit of capacitor: Is the farad (f) is a large unit: hence a smaller unit is used which either micro-farad (µf), nano-farad (nf) or pico-farad (pf), µ = 10-6 (millionth) n = 10-9 p = 10-12 Capacitor Construction Any two conducting surfaces that face each other across a small distance will be able to store an electric charge. The amount of charge that a capacitor stores depends on the: Page 11 of 85  INFORMATION SHEET Area of the two plates. Distance between the plates Material between the plates. Below shows two different types of capacitor designs. There are two main tapes of capacitors that we will be looking at: Polarized (Electrolytic capacitors) capacitors (Larger values than 1µF) Polarized (Electrolytic capacitors) symbol Physical look of a Polarized (Electrolytic capacitors) Page 12 of 85  INFORMATION SHEET Polarized capacitors MUST be connected to the correct polarity. That is positive of the capacitor to the positive of the supply. Un-polarized (Non Electrolytic) capacitors (Small values than, up to 1µF) Non-Polarized (Non Electrolytic) capacitors) symbol Physical look of Non-Polarized (Non Electrolytic) capacitors) Non-Polarized can be connected either way round. Application We will be looking at its application later on in the filtering section of the power supply. Inductor An inductor, also known as a coil, is an electric conductor (wire) that is wound into a coil. It’s a two terminal electrical component that stores electrical energy in a magnetic field when electric current is flowing through it. Unit of inductor: Is the henry (H) is a large unit; hence a smaller unit is used which either milli-henries (mH) or micro-henries (uH). Inductor symbol Physical look of an Inductor Page 13 of 85  INFORMATION SHEET Application We will be looking at its application later on in the filtering section of the power supply. Zener diodes Zener Diode symbol Physical look of a Zener Diode One application of Zener diode is in power regulations. Zener diodes are used in the reverse bias mode unlike the diode (used in the forward bias mode). When forward-biased, Zener diodes behave much the same as standard diodes. In reverse-bias mode, they do not conduct until the applied voltage reaches or exceeds the so-called Zener voltage, at which point the diode is able to conduct substantial current. Page 14 of 85  INFORMATION SHEET Shunt Stabilizer (Voltage Stabilizer) This is perhaps the most common use for the Zener diode. The output voltage (Vo) remains almost constant to the value of the Zener diode voltage (Vz) once the breakdown has occurred, for a wide variations in the input voltage (Vin). Application We will be looking at its application later on in the voltage stabilizer section of the power supply. Page 15 of 85  INFORMATION SHEET Transformer A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.... Transformers are used to increase or decrease the alternating voltages in electric power applications. Transformer symbol Physical look of a Transformer Page 16 of 85  INFORMATION SHEET Diode, Capacitor and Inductor application in power supply circuit Half-Wave Rectifier Circuit (Only ONE diode is used) To change the Raw DC to DC voltage We add a capacitor. The capacitor (C) is known as: Smoothing capacitor (Shunt capacitor) To reduce the ripple voltage, bigger size capacitor is added across the load (R). To change the Raw DC to DC voltage We add an inductor (Coil). In order to have an efficient power supply circuit, one way is to use a full wave rectifier circuit. Page 17 of 85  INFORMATION SHEET Full-Wave Rectifier Circuit (Uses Four diodes) To change the Raw DC to DC voltage We add a capacitor. Capacitor is used to reduce the ripple voltage Page 18 of 85  INFORMATION SHEET Full-wave rectifier using Centre tap Transformer Wave form identification Page 19 of 85  INFORMATION SHEET Task 7.1.1(1) Using the “Power and Control Electronics” Kit You need the following boards for the above circuit: Power Supply/Semiconductor Panel (connect to the left) a. Connect the circuit below. b. Name the above circuit: _________________________ c. Draw the output wave form below. d. Label the axes e. Measure the peak voltage (Vpk)= _________________ f. measure the periodic time (T) =__________________ g. Calculate the frequency of the wave (f) = 1/T= ______________ h. Power the circuit off. Housekeeping when finished. Page 20 of 85  INFORMATION SHEET Task 7.1.1(2) a. Connect the circuit below. b. Name the above circuit: _________________________ c. Draw the output wave form below. d. Label the axes e. Measure the peak voltage (Vpk)= _________________ f. Measure the ripple voltage (Vr)= _________________ g. measure the periodic time (T) =__________________ h. Calculate the frequency of the wave (f) = 1/T= _______________ i. Would the ripple voltage increase or decrease if the value of the C1 is made bigger? ____________________ j. Power the circuit off. Change the value of C1 from 470 uf to 220uf and repeat task “c” to “f” below. Page 21 of 85  INFORMATION SHEET k. Draw the output wave form below. l. Label the axes m. Measure the peak voltage (Vpk)= _________________ n. Measure the ripple voltage (Vr)= _________________ o. measure the periodic time (T) =__________________ p. Calculate the frequency of the wave (f) = 1/T= _______________ q. Would the ripple voltage increase or decrease if the value of the C1 is made bigger? ____________________ r. Power the circuit off. Housekeeping when finished. Page 22 of 85  INFORMATION SHEET Task 7.1.1(3) a. Connect the circuit below. b. Draw the output wave form below. c. Label the axes d. Measure the peak voltage (Vpk)= _________________ e. Measure the ripple voltage (Vr)= _________________ f. measure the periodic time (T) =__________________ g. Calculate the frequency of the wave (f) = 1/T= _______________ h. Would the ripple voltage increase or decrease if the value of the coil is made bigger? ____________________ i. Power the circuit off. Housekeeping when finished. Page 23 of 85  INFORMATION SHEET Task 7.1.1(4) a. Connect the circuit below. b. What is connected between Pin 7 and 8? ____________________ c. Draw the output wave across C1 (you may need to remove Zener diode out first?). d. Label the axes e. Draw the output wave form below between Pin 7 and 8. f. Label the axes Page 24 of 85  INFORMATION SHEET g. Measure the peak voltage (Vpk)= _________________ h. Measure the ripple voltage (Vr)= _________________ i. Comment on the output wave across Pin 7 & 8 to your instructor. j. Power the circuit off. Housekeeping when finished. Repeat the above tasks using full wave rectifier circuit. Transistor There are two types of transistors, a) NPN b) PNP Inductor symbol Physical look of an Inductor Where: B= b= Base C =c = Collector E = e = emitter Notice the transistor is made up of two diodes back to back. Page 25 of 85  INFORMATION SHEET There are two types of transistors: Silicon transistors Germanium transistors For silicon transistors to conduct, the base-emitter voltage (Vbe) must be 0.65v to 0.7v. For Germanium transistors to conduct, the base-emitter voltage (Vbe) must be 0.25v to 0.3v. Transistor as an Electronic Switch With no input current (Ib = 0A), there will be no output current (Ic = 0A), and hence the transistor is in the OFF state (equivalent to a switch being OFF). With an input current (Ib), there will be an output current (Ic), and hence the transistor is in the ON state (equivalent to a switch being ON). Page 26 of 85  INFORMATION SHEET Biasing Transistor Biasing defines the amount of input current (Ib) flowing into the base of the transistor. Rc = defines the output voltage Vo. Ic = is the output current which carries the signal to the output. Rb = defines the value of the input current Ib (known as the biasing resistor). Ib = is the input current that carries the input signal to the output. Ie = is the emitter current = Ic + Ib. Current Gain (hfe) Where: hfe = Output Current / Input Current = Ic / Ib Page 27 of 85  INFORMATION SHEET Testing NPN Transistor Task 7.1.1(5) Testing the base-Collector/emitter junction (forward bias) Set the digital multi-meter to the diode test range ( ). Connect the positive lead (Red) of the digital multi-meter to the base (b) of the transistor and connect the negative lead (Black) of the digital multi-meter to the collector (C) as shown in fig.1 Record your reading in the first row of Table 1 for forward bias connection. Keeping the positive lead (Red) of the digital multi-meter to the base (b) of the transistor, move the negative lead (Black) of the digital multi-meter to the emitter( e )as shown in fig.1 Record your reading in the first row of Table 1 for forward bias connection. Base-Emitter Base-Collector Collector-Emitter Forward Reverse Table 1 Page 28 of 85  INFORMATION SHEET From your measurement, what type of transistor material are you testing? (Silicon or Germanium) Task 7.1.1(6) Testing the base-Collector/emitter junction (reverse bias) Connect the positive lead (Red) of the digital multi-meter to the collector ( C ) of the transistor and connect the negative lead (Black) of the digital multi-meter to the base ( b )as shown in fig.1 Record your reading in the second row of Table 1 for forward bias connection. Keeping the negative lead (Black) of the digital multi-meter on the base ( b ) of the transistor, move the positive lead (Red) of the digital multi-meter to the emitter ( e )as shown in fig.1 Record your reading in the second row of Table 1 for forward bias connection. Page 29 of 85  INFORMATION SHEET Task 7.1.1 (7) Testing an electronic temperature transmitter amplifier circuit Using the “Power And Control Electronics” Kit. You need the following boards for the above circuit: Analog Sensor / Amplifier Panel (connect to the left) Temperature Control Panel (connect to the right) Steps: 1. Connect the above circuit. Page 30 of 85  INFORMATION SHEET 2. R1 = 5K potentiometer + 1K ohm resistor, Where the 5K Pot represents a thermistor which can be changed manually and immediately rather than waiting for the temperature to change. 3. The 5K potentiometer is used to set the DC input voltage (Vin). Turn it completely clockwise at first. 4. Rc = 1.5K + 1K potentiometer. Turn the 1K Pot completely clockwise at first. 5. Power the circuit ON. 6. Connect your DMM across R2 to measure (Vin) as shown above. Vin should be about 0.9V 7. Connect your DMM across Pin 11 and ground to measure (Vo) as shown above. Vo should be about 22.5V 8. Adjust the 5K potentiometer to give you Vin= 1v and measure the corresponding output voltage (Vo), increase Vin in steps of 0.1Volts. 9. Complete the table below. Input voltage (Vin) Output voltage (Vo) 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Page 31 of 85  INFORMATION SHEET 10. Plot a graph of the output voltage (vo) on the y-axis and input voltage (Vin) on the x-axis The Silicon-Controlled Rectifier (SCR) [SCR is a brand name for General Electric] Thyristors A thyristor is like two transistors, the four layers work like two transistors (an n-p-n and a p-n-p) that are connected together so the output from one forms the input to the other. The gate serves as a kind of "starter motor" to activate them. Page 32 of 85  INFORMATION SHEET If an SCR’s gate is left floating (disconnected), it behaves exactly as a Shockley diode. It may be latched by break over voltage or by exceeding the critical rate of voltage rise between anode and cathode, just as with the Shockley diode. The above method is not the correct/safe way to make the SCR operate (latch the SCR). The correct way is to apply a small voltage to the gate terminal which is connects directly to the base of the lower transistor, causing the lower transistor to be turned- ON by the resulting base current, causing the upper transistor to conduct, once the SCR is conducting the gate voltage no longer needed. The necessary gate current to initiate latch-up, of course, will be much lower than the current through the SCR from cathode to anode, so the SCR does achieve a measure of amplification. This method of securing SCR conduction is called triggering To turn a SCRs turned-OFF, by directly shorting their gate and cathode terminals together, or by “reverse-triggering” the gate with a negative voltage (in reference to the cathode), so that the lower transistor is forced into cutoff. Transistors versus thyristors With a transistor, when a small current flows into the base, it makes a larger current flow between the emitter and the collector. In other words, it acts as both a switch and an amplifier at the same time: If we remove the small current at the base (or gate), the large current immediately stops flowing from the emitter to the collector. Now often that's not what we want to happen. In something like an intruder alarm circuit (where maybe an intruder steps on a pressure pad and the bells start ringing), we want the small current (activated by the pressure pad) to trip the larger current (the ringing bells) and for the larger current to keep on flowing even when the smaller current stops (so the bells still ring even if our hapless intruder realizes his mistake and steps back off the pad). Page 33 of 85  INFORMATION SHEET In a thyristor, that's exactly what happens. A small current at the gate triggers a much larger current between the anode and the cathode. But even if we then remove the gate current, the larger current keeps on flowing from the anode to the cathode. In other words, the thyristor stays ("latches") on and remains in that state until the circuit is reset. Operation of thyristor in picture 1. With no current flowing into the gate, the thyristor is switched OFF and no current flows between the anode and the cathode. 2. When a current flows into the gate, base (input) of the lower (n-p-n) transistor, turning it ON. 3. Once the lower transistor is switched ON, current flow through into the base (input) of the upper (p-n-p) transistor, turning it ON as well. Page 34 of 85  INFORMATION SHEET 4. When the Both transistors are ON, the thyristor stays ON "latches"—even if the gate current is removed. (Stable states when Both transistors are ON) 5. Refer to Unit 3 (3.1.2.1 and3.1.2.2) Trainee handout to in bed the above theory practically, as well as to troubleshoot circuits using Lab Volts circuits Thyristor Summery 1. Thyristor is also known as SCR. 2. Thyristor is made from two transistors, PNP and NPN 3. Thyristor is turned ON (working) when a current flows into the gate. 4. Thyristor is turned ON (working) when Both transistors are ON. 5. The Symbol for a thyristor is: Page 35 of 85  INFORMATION SHEET 6. The thyristor (SCR) has FOUR (4) layers 7. The thyristor has THREE (3) terminals 8. Resistor R5 has been included in the circuit to allow the current waveform to be examined when operating the thyristor from an alternating supply. Output measurement is taken across resistor (R). 9. Diode D4 prevents current from flowing out via the gate circuit instead of the cathode. Page 36 of 85  INFORMATION SHEET Task 7.1.1 (8) 1. Draw the symbol of a thyristor:_____________________________ 2. How many terminals a thyristor has:_________________________ 3. Name the terminals of the thyristor:_________________________ 4. When both transistors are turned ON will the thyristor be Conducting or Not conducting? _____________________ 5. Give another name for thyristor: ______________________ Triac TRIAC is a three terminal electronic component that conducts conduct current in both directions when triggered. It’s a bidirectional thyristor. Note: (MT1) = Main Terminal 1 and (MT2) = Main Terminal 2 To make a triggering current for an SCR a positive only voltage has to be applied to the Gate and the Anode with respect to the cathode. Page 37 of 85  INFORMATION SHEET For a TRIAC, both positive and negative voltage can be applied to the gate and MT1 due to its structure see fig. Once triggered, thyristors and triac continue to conduct, even if the gate current ceases, until the main current drops below a certain level called the holding current. Since either Main Terminal can be positive or negative the end terminals can no longer be called anode and cathode. Since the Triac will conduct in either direction rectification no longer occurs and it can be used directly with an alternating supply to control a load, such as the lamp. The "current sinking" applies a direct voltage on the gate This gives ON/OFF switching control, depending on the size of the sinking current. Light Dimmer circuit using Triac. Page 38 of 85  INFORMATION INFORMATION SHEET SHEET Diac The Diac is a four-layer device that combines the properties of a Zener diode and a triac. If the voltage across the Diac is maintained below the "Zener" level, the Diac does not conduct. As soon as the voltage is raised above its critical value the Diac latches ON in a similar way to other devices in the thyristor family. It will remain in conduction until the voltage across it is reduced so that the current falls below the "holding" value. Again in a similar way to the triac, it is bi-directional. This means that it will conduct equally well in both direction. When the Diac conducts the capacitor (c) Fig (b) is discharged and remains short circuited by the Diac until it is automatically switched OFF at the end of the half-cycle. The charging cycle repeats from the start of the next half-cycle. If the value of the resistor is varied, the time taken for the capacitor voltage to rise above the Diac voltage will vary Fig(c), thus altering the timing of the pulse which is caused by the capacitor discharging via the Diac and its load resistor. This pulse is used to fire the triac. Page 39 of 85  INFORMATION SHEET Summery Triac 1. Triac will conduct in either direction used directly with AC supply to control a load, such as the lamp. 2. TRIAC is a three terminal electronic component that conducts conduct current in both directions when triggered. 3. It’s a bidirectional thyristor. 4. The symbol of Triac: 5. (MT1) = Main Terminal 1 and (MT2) = Main Terminal 2 6. For a TRIAC, both a positive or negative voltage can be applied to the gate and MT1 due to its structure 7. Applications of Triac are in light dimmers, controlling motor speed, etc. Diac 1. The main function of a diac is to fire the triac. 2. The Diac is a four-layer device. 3. It combines the properties of a Zener diode and a triac. 4. It is bi-directional (conduct) in both directions. 5. The symbol of Diac: 6. Applications of Diac with Triac are in light dimmers, controlling motor speed, etc. Page 40 of 85  INFORMATION SHEET Task 7.1.1 (9) 1. Draw the symbol of a thyristor: 2. Draw the symbol of a Triac: 3. Draw the symbol of a Diac: 4. How many terminals a thyristor has:_____________________ 5. How many terminals a Triac has: _______________________ 6. How many terminals a Diac has: _______________________ 7. Name the terminals of the thyristor: _________________________ 8. Name the terminals of the Triac: ___________________________ 9. Name the terminals of the Diac: ____________________________ 10.What other name is a thyristor known by: ____________________ 11.When both transistors are turned ON will the thyristor be Conducting or Not conducting? ____________________ 12.Write the three terminals of a triac? _________________________ 13.Name one application for triac: _____________________________ 14.What is the main function of a diac? _________________________ 15.Give one application for diac and Triac when used together. Page 41 of 85 INSTRUMENT FITTER Module 7.2 IDENTIFY, CONSTRUCT & TROUBLESHOOT OP-AMPS CIRCUITS. Page 42 of 85  INFORMATION SHEET Objective 7.2.1– Identify different types of op-amps circuits and troubleshoot them. Characteristic of an Operational Amplifier (Op-amp) An Op-amp comes so close to ideal performance that it is useful to state the characteristics of an ideal amplifier. 1. Infinite voltage gain 2. Infinite input impedance 3. Zero output impedance 4. Infinite bandwidth 5. Zero input offset voltage (i.e., exactly zero out if zero in). Op-amp symbol Physical look of an Op-amp Page 43 of 85  INFORMATION SHEET Darlington pair differential amplifiers: The inverting input will give the opposite polarity of output. The non-inverting input will give the same polarity of output. If the Op Amp is powered from ± power supplies then the circuit can be balanced about ground, removing any DC levels from both inputs and output. This is not essential to the operation of the device, which can be used on a single ended power source if required, although bias circuits will then be necessary. Input impedance is made high by using un-decoupled emitter resistors in the input circuits. Stage gain is made very high by multiple Darlington pair stages in cascade. Output impedance is low due to emitter followers being used as the output stage. Inverting amplifier circuit: also known as Closed-Loop Amplifier The output is sampled and fed back to the inverting input, to which the external input is also applied. The amplifier therefore receives its input from two sources, the external input via Rin and the feedback via Rf, giving an output that has the opposite polarity to the input. The stage gain of the amplifier is determined by the ratio of these two resistors: Vout = Av x Vin Page 44 of 85  INFORMATION SHEET (The minus sign [-] indicates Vout is of opposite polarity to Vin) With feedback applied the circuit is described as a Closed-Loop Amplifier. Using the formula given and the resistor values from the circuit board, calculate the anticipated gain Av: Inverting amplifier circuit: Where: Rin = Rf = Voltage Gain for an Inverting amplifier circuit: 𝑅𝑓 Voltage Gain (Av) = output voltage ÷ Input voltage = − 𝑅𝑖𝑛 (The minus sign [-] indicates Vout is of opposite polarity to Vin) Example1. If Rin = 10KΩ and Rf= 100KΩ. Find the voltage gain of the inverting amplifier. Example2. If Rin = 10KΩ and Av=-20. Find the value of Rf. Page 45 of 85  INFORMATION SHEET Non-Inverting amplifier circuit: Where: Rin = Rf = 𝑅𝑓 Voltage Gain (Av) = Vo ÷ Vin = 1+ 𝑅𝑖𝑛 Example1. If Rin = 10KΩ and Rf= 100KΩ. Find the voltage gain of the inverting amplifier. Example2. If Rin = 10KΩ and Av=20. Find the value of Rf. Page 46 of 85  INFORMATION SHEET Reference Point (Vref) or Ground point If reference point is connected to ground potential and if this reference is taken to any other potential (Vref) then two things happen: 1. Input voltages (Vin) applied to the inverting input will be referenced to this potential. The input circuit of the operational amplifier is based on the differential amplifier. The input voltage to the amplifier is therefore the difference between the two input voltages Vin and Vref, and 2. The output voltage Vout is also referenced to this potential, that is Vout = Vref when Vin - Vref = 0 Using fig 2.2 The effect of this is covered by the formula: Vout = Av(Vin - Vref) + Vref Example, if Vin is made the same as Vref (say +2V) then: Vout = Av (2 - 2) + 2V = Av (0) + 2V = 2V Av for fig 2.2 Av = - R3 / R1= - 600kΩ / 300kΩ = - 2. If Vref = -1V and Vin = +1, then: Vout = - 2(1 - (-1)) + (-1) = - 2x2 -1 = -5V The result will be limited by the saturation levels of the amplifier, as investigated in earlier experiments. Page 47 of 85  INFORMATION SHEET Inverting Amplifier - DC Operation From above the formula for the gain of an inverting operational amplifier given as: Av = - Rf / Rin This will now be further investigated and confirmed. In experiment using Op. Amp. Virtual ground concept The input terminal of the Op Amp is a virtual ground point, which means that: 1. The input current, Iin = Vin – 0 / Rin = Vin / Rin 2. The current in the feedback path, If = 0 – Vout / Rf = - Vout / Rf One of Kirchhoff's Laws states that the sum of currents flowing into a junction is equal to the currents flowing out of it. The Virtual Ground point is just such a junction: Iin = If + I' But the input impedance of the Op Amp is very high and there is virtually no voltage at this point in the circuit, so I' is negligibly small. ∴ Iin ≈ If ∴ Vin / Rin = - Vout / Rf ∴ Gain (Av) = Vout / Vin = - Rf / Rin Where the minus sign shows that Vout is of opposite polarity to Vin. This proves the formula that we have been using up to now. Page 48 of 85  INFORMATION SHEET Differential amplifier The action of a differential amplifier is to compare the voltage on one of its inputs with that on the other. Gain for multi-stage amplifier Gain for multi-stage amplifier (Av) = Av1 x Av2 Amplifiers connected in series Amplifiers connected in series are known as: Cascade Inverting Amplifier Gain and Bandwidth Bandwidth: The bandwidth of an operational amplifier circuit is defined as the range of frequencies over which the output voltage is greater than 1/ √2 x the mid-band output voltage. Bandwidth= (1/ √2) x the mid-band output voltage Page 49 of 85  INFORMATION SHEET The high and low frequencies at which the output voltage equals 1/ √2 x the mid-band output voltage are known as the upper limit frequency and lower limit frequency. The gain-bandwidth product of an op amp is a constant for a given device, and is quoted in the manufacturer’s datasheet for the IC. For the inverting amplifier circuit shown in Fig. 4.2, the upper limit frequency of the circuit’s bandwidth can be calculated if both the circuit gains, and the gain-bandwidth product of the op amp, are known. The lower limit frequency (f1) for the amplifier’s bandwidth will depend on the value of input capacitor Cin. The smaller the value of Cin, the higher will be the lower limit frequency of the circuit. Cin limits the lower frequency of the bandwidth Page 50 of 85  INFORMATION SHEET Summing Inverting Amplifier It was suggested in the introduction to the operational amplifier that the name was derived from the facility of the device to perform mathematical operations. The most basic mathematical operation is that of adding two quantities together, or summing. It has already been established (in Chapter 3) that: If = Iin=- Vout/Rf................................................................... (i) Kirchhoff's Current Law defines that Iin = I1 + I2 ∴ If = (I1 + I2)..................................................................... (ii) Due to the effect of the Virtual Ground point at the inverting input, V1 appears across R1, so I1 = V1/R1, and V2 appears across R2, so I2 = V2/R2. Page 51 of 85  INFORMATION SHEET Example Summing Inverting Amplifier Using the Inverting Amplifier formula for the gain of the circuit Gain (Av) = Vout / Vin = - Rf / Rin We can now substitute the values of the resistors in the circuit as follows, 1st. Gain (Av1) =10K/1K =-10 2nd. Gain (Av2) =10K/2K =-5 We know that the output voltage is the sum of the two amplified input signals and is calculated as: Vout = (Av1 X V1) + (Av2 X V2) Vout = (-10 X 2mV) + (-5 X 5mV) = -45mV Then the output voltage of the Summing Amplifier circuit above is given as -45 mV and is negative as its an inverting amplifier. Page 52 of 85  INFORMATION INFORMATION SHEET SHEET Task 7.2.1(1) Explain to your instructor. 1. What is the name given to the circuit in fig.1? ___________________ 2. Draw the output waveform for fig.1 3. What is the name given to the circuit in fig.2? ___________________ 4. Draw the output waveform for fig.2 5. List the Characteristic of an Operational Amplifier (Op-amp). 1._________________________________ 2._________________________________ 3._________________________________ 4._________________________________ 5._________________________________ 6. What part of the amplifier is Darlington pair placed in? Last stage or first stage? ___________________________ 7. What part of the amplifier is Emitter-follower amplifier placed in? Last (output) stage or first stage (input)? __________________ Page 53 of 85  INFORMATION SHEET 8. Label fig.3 accordingly. 9. Refer to fig.4; write the formula for the voltage gain. 10. Refer to fig.4 what does the negative (-) sign in the stage amplifier gain signify? 11. Refer to fig.4, given R1 = 10KΩ and Rf=110KΩ. Calculate the voltage gain. 12. Refer to fig.4, given R1 = 10KΩ and Av=7.5. Calculate Rf. 13. Refer to fig.4 what is the name given to Rf. ______________ 14. Refer to fig.4 what is the name given to R1. ______________ 15. Refer to fig.5; write the formula for the voltage gain. Page 54 of 85  INFORMATION SHEET 16. Refer to fig.5, given Rin = 5KΩ and Rf=120KΩ. Calculate the voltage gain. 17. Refer to fig.5, given R1 = 10KΩ and Av=7.5. Calculate Rf 18. What is the name given to the circuit in fig.5? ____________ ______________________________ 19. Draw the output waveform for fig.5 20. What is the function of a differential amplifier? ____________ ______________________________________________________ 21. Label the bandwidth on fig.6 Page 55 of 85  INFORMATION SHEET 22. Refer to fig.7 what is the function of Cin? ________________________ ________________________ ________________________ __________________________ 23. Refer to fig.9. What is the overall gain of the two stage amplifier? Overall gain= Page 56 of 85  INFORMATION SHEET Task 7.2.1 (2) Testing an inverting op-amp circuit Using the “Power And Control Electronics” Kit. You need the following boards for the above circuit: Analog Sensor / Amplifier Panel (connect to the left) Steps: 1. Connect the above circuit. 2. Connect your DMM across pin4 and pin 5 to measure (Vin) as shown above. 3. Set the variable power supply to -10V (input voltage Vin) 4. Connect your DMM across pin6 to measure (Vo) as shown above. 5. Adjust the variable power supply to -6V (input voltage Vin) and measure the corresponding output voltage (Vo). Page 57 of 85  INFORMATION SHEET 6. Complete the table below. Inverting Input Output voltage (Vo) voltage (Vin) -10 -6 1 Power the 5 circuit off. 10 Task 7.2.1 (3) Testing an non-inverting op-amp circuit Steps: 1. Connect the above circuit. 2. Connect your DMM across pin4 and pin 5 to measure (Vin) as shown above. 3. Set the variable power supply to -10V (input voltage Vin) 4. Connect your DMM across pin6 to measure (Vo) as shown above. 5. Adjust the variable power supply to -6V (input voltage Vin) and measure the corresponding output voltage (Vo). 6. Complete the table below. Page 58 of 85  INFORMATION SHEET Non-Inverting Input Output voltage (Vo) voltage (Vin) -10 -6 1 5 10 Power the circuit off. Housekeeping when finished. Page 59 of 85 INSTRUMENT FITTER Module 7.3 IDENTIFY & TROUBLESHOOT DIFFERENT TYPES OF FILTER CIRCUITS. Page 60 of 85  INFORMATION SHEET Objective 7.3.1– Identify different types of filter circuits and troubleshoot them. Types of Filter The object of a filter circuit is to allow a specific band of frequencies to pass and to restrict (filter-out") unwanted frequencies. Filters are so named according to the frequency range of signals that they allow to pass through them, while blocking or "attenuating" the rest. There are four basic types of filter. 1. Low-Pass Filter Passes all signals at frequencies below the cut-off frequency and restricts all those above. 2. High-Pass Filter Page 61 of 85  INFORMATION SHEET Passes all signals at frequencies above the cut-off frequency and restricts all those below. 3. Bandpass Filter This passes a middle band of frequencies and therefore has two cut-off frequencies, normally denoted by fL for the lower cut-off frequency and fH for the upper. All signal frequencies between fL and fH are passed and those lower than fL or higher than fH are restricted. This type of filter is essential in communications systems, such as radio ("wireless"), television, radar, data-coms, etc., for the selective (selection of a desired signal) process. 4. Band Stop Filter Page 62 of 85  INFORMATION SHEET Sometimes called "band restrict" or "band elimination" filters. This again has two cut-off frequencies, but this time the signals are restricted between the two and allowed to pass below the lower cut-off frequency fL and above the upper fH. The amount of ripple in a filter circuit is measured in Decibels The function of a filter in a power circuit to reduce ripple The filter in a power supply will Increase the DC output Simple RC (First Order) Filters Page 63 of 85 There are two configurations possible for a series RC circuit: Circuit (a) High-Pass Filter circuit The reactance of the capacitor is high at low frequencies. Since the capacitor is the series element in the "L" segment this will restrict the low frequency components from reaching the output, which is taken across the resistor. This circuit is therefore a High-Pass Filter. Circuit (b) Low-Pass Filter circuit With the capacitor in the shunt arm, at high frequencies there is a progressive short circuit across the output as frequency increases, and the input voltage will largely be dropped across the series element resistor. This circuit is therefore a Low-Pass Filter. Page 64 of 85  INFORMATION SHEET Task 7.3.1 (1) (Types of Filter) Q1. Calculate the reactance impedance (Xc) of the given filter. C= 0.8nf and frequency (f) =100Hz Q2. What type of filter circuit is used in Q1 above if it only allows frequencies from 0Hz up to 100Hz? (Low pass or High pass) and why? ___________________________ Q3. Calculate the reactance impedance (Xc) of the given filter. C= 0.8nf and frequency (f) =20MHzHz Q4. What type of filter circuit is used in Q3 above? (Low pass or High pass) and why? ___________________________ Q5. Draw your circuit for Q3. Q6. Calculate the reactance impedance (Xc) of a given filter. given: C= 80pf and frequency (f)=100Hz Q7. Calculate the reactance impedance (Xc) of a given filter. C= 80pf and frequency (f) =100MHzHz Page 65 of 85  INFORMATION SHEET Cut-Off Frequency (fc =fo) for RC circuit (for both High and Low pass filter) Cut-Off Frequency The cut-off frequency is defined as that frequency at which the output voltage is 3dB down (-3dB) on the input. This implies a voltage ratio of 0.707:1 or 1 /√2. Examination of the phasor diagram of Fig 2.3 shows that this occurs when: Vc = Vr Since these are series elements the same current flows through each. Vc = I.Xc, Vr = I.R ∴ I.Xc = I.R ∴ Xc = R ∴ 1 / 2πfC = R, ∴ fc = 1 / 2πCR Note: This formula for the cut-off frequency will be the same whether the output is taken across the resistor (High-Pass Filter) or the capacitor (Low-Pass Filter) since Vc = Vr. LC Band Pass Filter Frequency Response of a Parallel Tuned Circuit The parallel LC circuit has impedance that is variable with frequency, peaking at resonance. This makes it ideally suitable as a Band Pass Filter. Page 66 of 85  INFORMATION SHEET Ex.1 If L = 1mH and C = 10nF. Calculate the resonant frequency in kHz. Resonant frequency =___________ kHz. Task 7.3.1 (2) (Cut-Off/ resonant Frequency) 1. Draw the symbol for a Band Pass Filter 2. Draw the symbol for a High Pass Filter 3. Draw the symbol for a Low Pass Filter 4. Calculate the resonant frequency given: C = 22uf and L = 3mH 5. Calculate the resonant frequency given: C = 20nf and L = 2mH 6. Calculate the value of capacitance given: L = 2mH and fo = 37KH Page 67 of 85  INFORMATION SHEET 7. Construct a low pass filter using the given components. 8. Construct a high pass filter using the given components. 9. Troubleshoot both above circuits (low & high pass filters) i. Write down the input frequency used fin= ii. Write down the output frequency used fo= iii. Comment on your findings Page 68 of 85 INSTRUMENT FITTER Module 7.4 IDENTIFY, CONSTRUCT & TROUBLESHOOT DIFFERENT TYPES OF OSCILLATOR CIRCUITS. Page 69 of 85  INFORMATION SHEET Objective 7.4.1– Identify different types of oscillator circuits and troubleshoot them. Electronic Oscillator characteristics Oscillators are electronic circuits that generate an output signal without the necessity of an input signal. It produces a periodic waveform on its output with only the DC supply voltage as an input. The output voltage can be either sinusoidal or non-sinusoidal, depending on the type of oscillator. Different types of oscillators produce various types of outputs including sine waves, square waves, triangular waves, and saw- tooth waves. Incorporate feedback from output to input Require an amplifier component to recover ‘losses A basic oscillator is shown in Figure 1. Page 70 of 85  INFORMATION SHEET Types of feedback used by oscillators Oscillators use positive feedback, where the positive feedback reinforces the input Inverting’ Amplifiers require out-of-phase feedback Non-Inverting Amplifiers require in-phase feedback Inverting’ Amplifiers require out-of-phase feedback Inverting Amplifier with a ß network provides a phase shift of 180° Page 71 of 85  INFORMATION SHEET Non-Inverting Amplifiers require in-phase feedback Non-inverting amplifier has 0° β network An oscillator has a non-inverting amplifier with a gain of 3. For oscillation to take place, the β network must have an attenuation of 1/3 = 0.33 and a phase shift of 0°. An oscillator has a β network with an attenuation of 0.5 and a phase shift of 180°. For oscillation to take place the amplifier must be an inverting amplifier with a gain of 1/0.5= 2. Conditions for Oscillation Two conditions, illustrated in Figure 4, are required for a sustained state of oscillation: 1. Phase shift around the feedback loop must be zero. 2. Voltage gain, around the closed feedback loop (close loop gain) must be 1 (unity). Where: Acl = Voltage gain around the closed feedback loop β = Attenuation That is a fraction of the output signal is feedback to the input with no net phase shift, resulting in a reinforcement of the output signal. Page 72 of 85  INFORMATION SHEET After oscillations are started, the loop gain is maintained at 1.0 to maintain oscillations. A feedback oscillator consists of an amplifier for gain (either a discrete transistor or an op-amp) and a positive feedback circuit that produces phase shift and provides attenuation, as shown in Figure 2. LC Oscillator This circuit employs zero phase shifts and a non-inverting amplifier. The ß network is a tuned circuit consisting of L1, C2, which gives zero phase shifts at resonance. At any other frequency the circuit behaves either inductively or capacitively with the accompanying phase shift between current and voltage. The resonant frequency is given by the formula: fo = 1 /2π√ LC Ex.1. Given L = 3mH and C =2 nF for an LC oscillator circuit find the frequency of oscillation. Frequency of oscillation: fo = 1 / (2π√ LC) = ___________ kHz. Page 73 of 85  INFORMATION SHEET Task 7.4.1 (1) 1. Given L = 2mH and C =4 nF for an LC oscillator circuit find the frequency of oscillation. Frequency of oscillation: fo = 1 / (2π√ LC) = ___________ kHz. 2. Given L = 0.5mH and C =3 nF for an LC oscillator circuit find the frequency of oscillation. Frequency of oscillation: fo = 1 / (2π√ LC) = ___________ kHz. RC Ladder Oscillator This circuit employs a three (3) stage RC filter network, each individual RC network contributing towards a total phase shift of 180°. The phase shift of each section will be different, since the loading on the output of each is different, but the total will be 180° at only one frequency. Theoretically a shift of 90° is possible from one section; however the output voltage would be zero, which is not very useful! The amount of the phase shift is dependent on the reactance of the capacitor that varies with frequency. Hence there is only one frequency at which the shift will be exactly 180°. The development of this formula is a little complex, but the frequency is given by the formula: Frequency of oscillation: fo = √6 / 2πCR Where C is the value of each capacitor, and R is the value of each resistor (the formula assumes three capacitors of equal value and three resistors of equal value). Page 74 of 85  INFORMATION SHEET Ex.1. Given C = 2.23nF and R = 11.2KΩ for an RC ladder oscillator circuit find the frequency of oscillation. Frequency of oscillation: fo =√6 / (2πCR) = ___________ kHz. Task 7.4.1 (2) Q1. Given C = 3 nF and R = 11 KΩ for an RC ladder oscillator circuit. Find the frequency of oscillation. Frequency of oscillation: fo = 6 / (2πCR) = ___________ kHz. Q2. Given C = 4 nF and R = 8 KΩ for an RC ladder oscillator circuit. Find the frequency of oscillation. Frequency of oscillation: fo = 6 / (2πCR) = ___________ kHz. Page 75 of 85  INFORMATION SHEET Objective 7.4.2– Construct different types of oscillator circuits and troubleshoot them. Task 7.4.2 (1) Summing Amplifier Circuit Objective: Given tools, materials, and circuit diagram fig. 1, you will correctly construct and test a Summing Amplifier circuit. Equipments required: Duel Power supply Bread board Oscilloscope, multi-meter and Test leads Components required: 1 X 741 operational amplifier 1 X 1K ohm resistors 1 X 2 K ohm resistors 1 X 10 K ohm resistors Task steps: 1. Collect all the above from the test monitor 2. Check all your collected item for safety 3. Connect your components according to circuit diagram fig.1 Page 76 of 85  INFORMATION SHEET 4. Connect the duel power supply wiring according to fig.2 5. Troubleshoot your circuit from any connection errors 6. Power your circuit 7. Connect 2mV to the 1K ohm resistor 8. Connect 5mV to the 2K ohm resistor 9. Measure the voltage at the pin 2: ___________________ 10. Measure the voltage at the pin 6: __________________ 11. Perform housekeeping Page 77 of 85  INFORMATION SHEET Task 7.4.2 (2) LC Oscillator Circuit Objective: Given tools, materials, and circuit diagram fig. 2, you will correctly construct and test a LC Oscillator Circuit. Equipments required: Laboratory Instrument System Operational Amplifier board Konnect-All board Electrical parts box Oscilloscope, multi-meter and Test leads Components required: 1 X PNP transistor (2N2905A) 3 X 10 kΩ pot resistors 2 X 10uf Capacitor 1 X 22uf Capacitor 1 X 470uf Capacitor 1 X 0.22uf Capacitor 1 X 0.47uf Capacitor Task steps: 1. Collect all the above from the test monitor 2. Check all your collected item for safety 3. Connect your components according to circuit diagram fig.2 Page 78 of 85  INFORMATION SHEET 4. Connect the power supply wiring according to fig.2 5. Troubleshoot your circuit from any connection errors 6. Adjust the power supply for 10 Vdc. 7. Turn the 10 kΩ pot fully clockwise (right). What is the output Frequency? …………………………………………………………………………………………… 8. Slowly turn the 10 kΩ pot counter-clockwise (left) until a strong audio sound is heard. What is the value of the output voltage? VOLTAGE=…………………………… What is the value of the output Frequency? FREQUENCY …………………………… 9. Turn the 10 kΩ pot fully clockwise. 10. Change the 0.22 µF to a 0.47 µF capacitor. 11. Slowly turn the 10 kΩ pot until a sound is heard. Explain to your test monitor what had happened? ………………………………………………………………………………….………………………… 12. Use the oscilloscope to measure: Output Voltage =…………………………… Output frequency=…………………………… 13. Perform housekeeping. Page 79 of 85  INFORMATION SHEET Task 7.4.2 (3) Astable Multivibrator Circuit using transistors. Objective: Objective: Given tools, materials, and circuit diagram fig. 1, you will correctly construct and test a Astable Multivibrator circuit. Equipments required: Duel Power supply Bread board Oscilloscope, multi-meter and Test leads Components required: 2 X NPN ___________ transistors 2 X R1 =_______K ohm resistors 2 X R2 = ______K ohm resistors 2 X R3 = ______K ohm resistors 2 X C1 = ______UF Capacitor 2 X LED”S Task steps: 1. Collect all the above from the test monitor 2. Check all your collected item for safety 3. Connect your components according to circuit diagram fig.3 Page 80 of 85  INFORMATION SHEET 4. Connect the 6V power supply wiring according to fig.3 5. Troubleshoot your circuit from any connection errors 6. Power your circuit 7. Measure the peak voltage at Tr1 collector: ___________________ 8. Measure the peak voltage at Tr2 collector: __________________ 9. Draw the waveform at Tr1 collector 10. Perform housekeeping. Page 81 of 85  INFORMATION SHEET Task 7.4.2 (4) Astable Multivibrator Circuit with an LM741 Op Amp Chip Objective: Given tools, materials, and circuit diagram fig. 1, you will correctly construct and test a Astable Multivibrator circuit. Equipments required: Duel Power supply Bread board Oscilloscope, multi-meter and Test leads Components required: 1 X 741 operational amplifier 1 X R1 =_______K ohm resistors 1 X R2 = ______K ohm resistors 1 X R3 = ______K ohm resistors 1 X R4 = ______K ohm resistors 1 X C1 = ______UF Capacitor 1 X LED Task steps: 1. Collect all the above from the test monitor 2. Check all your collected item for safety 3. Connect your components according to circuit diagram fig.4 Page 82 of 85  INFORMATION SHEET 4. Connect the duel power supply wiring according to fig.2 5. Troubleshoot your circuit from any connection errors. 6. Power your circuit 7. Measure the voltage at output of op-amp (pin 6): _____________ 8. Measure the voltage across R4: __________________ 9. Measure the voltage across LED: _________________ 10. Draw the waveform across the LED 11. Perform housekeeping. Page 83 of 85  INFORMATION SHEET Task 7.4.2 (5) Wien Bridge Oscillator Circuit Built with an LM741 Objective: Given tools, materials, and circuit diagram fig. 1, you will correctly construct and test a Wien Bridge Oscillator circuit. Equipments required: Duel Power supply Bread board Oscilloscope, multi-meter and Test leads Components required: 1 X 741 operational amplifier 1 X RI =_______K ohm resistors 1 X RF =_______K POT ohm resistors 1 X R1 = ______K ohm resistors 1 X R2 = ______K ohm resistors 1 X C1 = ______UF Capacitor 1 X C2 = ______UF Capacitor Task steps: 1. Collect all the above from the test monitor 2. Check all your collected item for safety 3. Connect your components according to circuit diagram fig.4 Page 84 of 85  INFORMATION SHEET 4. Connect the duel power supply wiring according to fig.2 5. Troubleshoot your circuit from any connection errors. 6. Power your circuit 7. Measure the peak voltage at the output (pin 6): __________ 8. Measure the voltage at the input (pin 3): ___________ 9. Draw the waveform across the voltage at output (pin 6): 10. Perform housekeeping. Page 85 of 85