Introduction to Spring Term Analogue Electronics Project
Contents
1. Plot a graph of V vs Io and determine the internal resistance of the secondary side of the transformer j By how much does the actual voltage differ from the ideal voltage source value at low load resistances RNG JKAE 01 13 University of York2. Foundation Year 2012 13 Introduction to Spring Term Analogue Electronics Project In the spring term you will be carrying out an analogue electronics project building a simple DC power supply unit Figure 1 shows the simplified functional block diagram of the Power Supply Unit PSU and which block s you will be working on in each laboratory exercise input output Step down Rectifier circuit Smoothing Voltage regulator DC 5V Transformer Half Full wave Capacitor AC mains 230V 50Hz 1 Pe p l Laboratory 4 Laboratory 5 Laboratory 6 Figure 1 DC Power supply You will be building the PSU step by step one functional block at a time while familiarising yourself with standard laboratory equipment and measurement procedures Due to safety reasons you will be provided with a pre assembled step down transformer module that is shown in Figure 2 Figure 2 Transformer module Figure 3 depicts a photograph of the PSU Design Exercise Printed Circuit Board PCB that will also be provided to you at the start of the first laboratory session The PCB has copper tracks on both sides of the boards but as the layout is fairly simple you can easily trace a track on the board The PCB is populated with the following components one from each type is marked in Figure 3 University of York Foundation Year 2012 13 AC INPUT METER Figure 3 PSU Design Exercise PCB 1 Block connectors to connect the step down transformer a
3. and mean values Period and frequency of the waveform j What is the theoretical mean value of a pure sinusoidal signal Briefly explain why the measured mean value of the signal deviates from the theoretical value Determine the approximate turns ratio of the transformer assuming the primary side is connected to ac mains 230V 50Hz University of York Foundation Year 2012 13 2 Measuring the internal resistance of a voltage source It is important to determine the input and output resistance of most electronic circuits to characterise them e g amplifiers The secondary side of the transformer can be modelled as a voltage source with an internal resistance In this section you will be devising an experimental setup to measure the internal output resistance of the transformer s secondary side You will follow a similar procedure to find the input and output resistance of many electronic circuits as you progress through your degree programme Figure 1 shows an arrangement to measure the internal resistance of a voltage source R Io a Figure 1 Voltage source connected to a load resistor The relationship to determine the voltage across the load V driven by the voltage source Vo is given by Vo Vs 1oRs 1 or with a simple manipulation the above equation can be written as Vo R V 2 Equation 2 can be used to determine the value of the internal resistance of the source using a graphical metho
4. ase note that the lectures are tailored to help you with the laboratory sessions and missing them will place you at significant disadvantage RNG JKAE 01 13 University of York Foundation Year 2012 13 University of York Foundation Year 2012 13 Laboratory 4 AC Signals and Internal Resistance Aims and Objectives The aims of this laboratory are to familiarise yourself with measurements related to a c voltages and the internal resistance of a voltage source By the end this laboratory you should be able to do the following measure peak to peak rms and mean values of ac voltage waveforms measure the period and frequency of an ac voltage waveform devise a simple experiment to measure the internal resistance of a voltage source Guide to progress You have one half day session to complete this laboratory Theory related to this laboratory will be covered in the week 2 lecture If you are stuck on a problem for more than a few minutes or if you feel you are falling behind then seek guidance from a demonstrator or a member of academic staff 1 AC signals In this section you will set up a simple experiment to determine the dc equivalent voltage of a sinusoidal signal that delivers the same power to a resistive load This quantity is called the effective or rms Root Mean Squared value of the sinusoid This experiment will be performed using two identical lamps One lamp will be connected to the sinusoidal output from the t
5. d as explained in the lecture For this part of the experiment you are required to use the transformer and the PSU Design Exercise Printed Circuit Board PCB a First remove any links placed on the link headers in the PCB b Connect the secondary side of the transformer to connectors Yellow in the AC INPUT area of the PCB using suitable leads c Use a wooden cover resistor box as the variable load resistor and initially set it to a sufficiently high value 3 4kQ Connect the resistor box across the two connectors in the LOAD area of the PCB d Place the Links on headers J1 and J2 to route the ac signal to the load resistor By observation you should be able to determine it is the bottom two pins on each header that you need to link University of York Foundation Year 2012 13 e Set up the DMM as an Ammeter and connect it appropriately to measure the load current If you cannot determine how to connect the ammeter please ask f Determine which test points TP1 amp 3 OR TP7 amp 8 that you would use to measure the load voltage V and explain the reason s for your selection g Now your setup is ready for taking some measurements Draw a diagram in your logbook to represent the experimental setup that you have just finished h Obtain a set of readings for V and J by varying the load resistance R Make sure that you take extra care not to short circuit the output of the transformer always R gt 0 i
6. meter DMM or the Oscilloscope Since the comparative brightness of the lamps is difficult to judge accurately you may wish to repeat the experiment several times resetting the DC power supply to zero each time to test the repeatability of the experiment e Using your knowledge of power in resistive loads comment on the voltages measured in c and d and how they are related f Use the Digital Multi meter set to ac voltage to measure the voltage across the lamp connected to the transformer How does this measurement compare with your previous measurements g In order to compare measurements in this way using the relationship for power in resistive circuits we must be able to apply Ohm s Law to the device in question Comment on whether you think this will apply well in this case possibly referring to measurements you might make h You may have learned that the DMM can be used to measure the rms value of an ac signal The Oscilloscope can be configured to make a variety of measurement of a waveform including the rms value This feature can be enabled by pressing the MEASURE button and selecting the appropriate measurement s for a selected channel If you require further details please refer to the user manual of the oscilloscope pg 24 25 i Now using the MEASURE function of the oscilloscope obtain the following measurements for the voltage waveform across the lamp connected to the transformer Peak to peak rms
7. nd load resistor using suitable leads 2 Test points numbered with prefix TP e g TP1 TP11 to connect probes to the measurement equipment 3 Link Headers numbered with prefix J e g J1 J7 to route the signal to different areas in the PCB Please note that 4 pin headers require only one link at a time and it can be either between the top or bottom two pins 4 Component posts allow you to securely fix the components to the PCB 5 Pins to make connections with in the PCB using limrose connectors or to connect an Ammeter University of York Foundation Year 2012 13 Schedule for Term 2 Week 2 Lecture ac signals in resistive circuits internal resistance of voltage sources Week 3 Laboratory 4 AC signals Week 4 Lecture half and full wave rectifiers Week 5 Laboratory 5 Half and Full wave rectifier circuits Week 6 Laboratory 5 continues Week 7 Lecture RC circuits Week 8 Laboratory 6 Smoothing capacitor and Voltage regulator IC Some general information As you will be working on the PCB throughout the term it is important that you store your PCB securely in the storage area allocated to you in the cupboard underneath the laboratory bench after each session Please read the section introduction to Foundation Course Laboratory Work on page 1 of autumn term laboratory scripts booklet specifically the guidance on how to maintain a lab book and a description of the assessment of it Ple
8. ransformer You will be using the secondary side of the transformer for this purpose Note that the secondary side has three outputs terminals yellow terminals are outer taps of the secondary winding and the black terminal is the centre tap The other lamp will be connected to a DC power supply Steps to set up the experiment and to make necessary measurements are given below a Connect a lamp with the holder across a yellow and the black terminals of the transformer and switch on the power to the circuit b Use the oscilloscope to observe the waveform across the lamp As you may need to measure higher voltages in this experiment use the x10 probes and set the probe s multiplication factor in the Oscilloscope to x10 press the CH1 MENU button and then selecting the factor If you require more details refer to the user manual of the Oscilloscope c Manually by inspection measure the peak to peak voltage and then determine the peak voltage of the waveform across the lamp TIP It is a good practice to draw the waveforms that you observe and note down any measurements you make on them d Connect the other lamp with the holder across a DC power supply initially set to OV Adjust the voltage of the DC power supply until the lamp appears to be the same 5 University of York Foundation Year 2012 13 brightness of the lamp connected to the output of the transformer Measure the DC voltage across the lamp using a Digital Multi
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