Lab 2 - 2B 2010

Lab 2 - 2B 2010 - ECE 2B Lab #2 Lab 2 Dual-Output Linear...

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1 © Bob York ECE 2B Lab #2 Lab 2 Dual-Output Linear Power Supply Overview In this lab you will construct a regulated DC power supply to provide a low-ripple adjustable dual-output voltage in the range 5-12 VDC at 0.2 Amps (maximum) load current from a 120 VAC power outlet. This will be used to provide power to circuits you will construct in later labs in ECE 2. Figure 2-1 – Photo of the finished product (some components not shown).
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2 Dual-Output Linear Power Supply © Bob York 2 Power supplies are essential components of any microelectronic system. This lab is intended to provide a basic understanding of the design and operation of linear supplies, and techniques for construction of hardwired electronic circuit modules. In this lab you will gain experience with: Power transformers Diode bridge rectifiers Capacitive loading for ripple rejection Use of IC voltage regulators Basic soldering techniques The objective of the lab is not simply to create a working circuit; it is to learn about circuits. So, as you progress through the lab, try to understand the role of each component, and how the choice of component value may influence the operation of the circuit. Ask yourself questions such as: Why is this resistor here? Why was this particular integrated circuit chosen? How could the system be improved? It is only when you can answer such questions that you will progress towards designing your own circuits. Table of Contents Background information 3 Basics of Linear Power Supply Design 3 Voltage Regulation 4 Pre-lab Preparation 6 Before Coming to the Lab 6 Parts List 6 Full Schematic and Board Layout for Lab #2 7 In-Lab Procedure 8 2.1 AC Power Transformer 8 2.2 Full-Wave Bridge Rectifier 9 2.3 Filtering Capacitors 10 2.4 Adjustable Voltage Regulators 12 LM317 Positive Regulator Circuit 12 LM337 Negative Regulator Circuit 13 2.5 Finishing Touches 14 Optional Enclosure 14
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Background information 3 © Bob York 3 Background information Basics of Linear Power Supply Design The simplest type of DC power supply is a so-called “linear” supply, shown schematically in Figure 2-2. 1 A transformer is used to step down the AC line voltage to a smaller peak voltage m V , which must be somewhat larger than the ultimately desired DC output. A diode circuit rectifies the AC signal and a capacitive filter bank is then used to “smooth” or “filter” the rectified sinusoid, producing a waveform with predominant DC component. Under normal loading conditions there is always some residual periodic variation or “ripple” in the filtered signal. If the application requires very low ripple and constant DC output over a wide range of loading conditions, then active regulation is required to further reduce or eliminate this residual ripple. Most active regulator circuits will require a certain minimum input-output voltage differential for proper operation.
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Lab 2 - 2B 2010 - ECE 2B Lab #2 Lab 2 Dual-Output Linear...

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