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Instructor: Paul Gordy Office: H-115 Phone: 822-7175 Email: PGordy@tcc

Lecture #10 EGR 262 – Fundamental Circuits Lab. EGR 262 Fundamental Circuits Lab Presentation for Lab #10 Getting Power off the Wall. Instructor: Paul Gordy Office: H-115 Phone: 822-7175 Email: PGordy@tcc.edu. Lecture #10 EGR 262 – Fundamental Circuits Lab.

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Instructor: Paul Gordy Office: H-115 Phone: 822-7175 Email: PGordy@tcc

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  1. Lecture #10 EGR 262 – Fundamental Circuits Lab EGR 262 Fundamental Circuits Lab Presentation for Lab #10 Getting Power off the Wall Instructor: Paul Gordy Office: H-115 Phone: 822-7175 Email: PGordy@tcc.edu

  2. Lecture #10 EGR 262 – Fundamental Circuits Lab Providing Power to Circuits For each experiment so far in this course we have used DC power supplies available in lab to provide 5V, 9V, and other voltages. If we were designing a microprocessor-based piece of equipment or device, we might want to include our own DC power supply so that we could simply plug the device into an AC outlet. In this lab we will see how to build a power supply that provides 5V DC from a 120V AC source. AC Voltages AC, or alternating current, voltages are sinusoidal in nature. Let’s begin with some terminology used to describe such sinusoidal waveforms.

  3. Lecture #10 EGR 262 – Fundamental Circuits Lab Sinusoidal Waveforms In general, a sinusoidal voltage waveform can be expressed as: v(t) = Vpcos(wt) where Vp = peak or maximum voltage w = radian frequency (in rad/s) T = period (in seconds) f = frequency in Hertz (Hz) Example: An AC wall outlet has VRMS = 120V and f = 60 Hz. Express the voltage as a time function and sketch the voltage waveform.

  4. Lecture #10 EGR 262 – Fundamental Circuits Lab • Transformers: Transformers are used to: • Change voltage values (our main interest for Lab #10) • Change current values • Change resistance (or impedance) values • Isolate circuits f = magnetic flux (in webers, Wb) where a = turns ratio

  5. Transformer used in Lab #10 Primary: 120V Secondary: 12V, 1000 mA Lecture #10 EGR 262 – Fundamental Circuits Lab Examples of transformers (reference: www.allelectronics.com) Primary: 120V Secondary: 28V, 1.5A Primary: 120V Secondary: 40VCT, 0.25A Utility pole transformer

  6. Lecture #10 EGR 262 – Fundamental Circuits Lab Examples of transformers (reference: www.allelectronics.com) PC Mount Transformer Primary: 120V Secondary: 16VCT, 0.8A or 8V, 1.6A Toroidal Transformer Primary: 120V Secondary: 8.5V and 9.4V Variac (Variable Transformer) Input: 110V Output: 0 to 130V Up/Down Transformer (110V to 220V) or (220V to 110V)

  7. Lecture #10 EGR 262 – Fundamental Circuits Lab

  8. The transformer to be used in this lab has the following specifications: • Input: 120 V RMS, 60 Hz • Output: 12 V RMS, 1000 mA • So we can easily calculate the turns ratio: • Also note that for the input: • And similarly for the output: • The transformer is illustrated below. Vin Vout 170 V 17 V t t 10 : 1 -17 V -170 V + + Vin = 120 V RMS 12 V RMS = Vout _ _ Lecture #10 EGR 262 – Fundamental Circuits Lab

  9. Lecture #10 EGR 262 – Fundamental Circuits Lab • Rectifiers • The transformer just illustrated is used to step down the voltage, but it is still an AC voltage. We need to convert it to a DC (direct current) voltage. A rectifier is used for this purpose. Rectification is defined as the process of converting an AC waveform into a DC waveform. There are three common types of rectifier circuits: • Half-wave rectifier (HWR) • Full-wave bridge rectifier (FWR-bridge) • Full-wave center-tap rectifier (FWR-CT)

  10. Lecture #10 EGR 262 – Fundamental Circuits Lab Half-Wave Rectifier Discuss the operation of the half-wave rectifier shown below.

  11. Lecture #10 EGR 262 – Fundamental Circuits Lab Filter Capacitor A filter capacitor is often added to the output of a half-wave rectifier in order to “smooth” the output. Discuss the operation of this circuit.

  12. Lecture #10 EGR 262 – Fundamental Circuits Lab Full-wave Rectifier with Filter Capacitor Discuss the operation of the circuit below (which will be used in lab). Discuss ripple voltage and the selection of capacitor values. + 100 F _ About 20V with our transformers

  13. Filter Capacitor 5 V Regulator Full-wave Rectifier 5 V DC output Transformer 120 V RMS AC input V1 V2 V3 V4 V5 V1 V3 V5 170 V 20 V 5 V t t t -170 V V2 V4 20 V 20 V Vr t t -20 V Lecture #10 EGR 262 – Fundamental Circuits Lab • Regulators • Note that even with the addition of a large filter capacitor, the DC voltage generated has some ripple (which is undesirable). Regulators can be used to eliminate most of the ripple voltage. Note the block diagram shown below. • Two types of regulators will be used in this lab: • Zener diode regulator • Integrated circuit (IC) regulator

  14. Lecture #10 EGR 262 – Fundamental Circuits Lab Diodes - Review When LED’s were introduced in Lab #1, it was noted that a diode acts somewhat like a voltage-controlled switch. When the diode is forward-biased (VD > 0) it acts like a short circuit (or a closed switch). When the diode is reverse-biased (VD < 0) it acts like an open circuit (or open switch). This is true to some extent, but if the reverse-bias voltage becomes too large, the diode can enter the breakdown region where it again acts like a short circuit. For many diodes (signal and rectifier diodes), the breakdown voltage is to be avoided and is often treated like a max negative voltage not be be exceeded. A rectifier diode for example, might become forward biased with a mere 0.7V, but it might require 1000V to go into breakdown. It can easily be used to rectifier 120V AC voltages without ever entering the breakdown region. Figures 5 and 6 below are from the Lab #1 section of the lab manual.

  15. Lecture #10 EGR 262 – Fundamental Circuits Lab Zener Diodes A Zener diode is a special type of diode that is intended to operate in the breakdown region. The breakdown voltage is much lower than with other diodes and Zener diodes are designed to have particular breakdown voltages. For example, you might buy a 5.1V Zener diode or a 12V Zener diode, where the voltage listed is the breakdown voltage. Also note that the Zener diode has a special symbol.

  16. The 1N4007 has a Peak Reverse Voltage (PRV) of 1000V Lecture #10 EGR 262 – Fundamental Circuits Lab Diode specifications The following tables are from a Jameco Electronics catalog (www.jameco.com). Note that Zener diodes are purchased with a particular value of VZ in mind. Rectifier diodes, on the other hand, list the Peak Reverse Voltage (PRV) – a max reverse voltage to be avoided. The 1N4733A is a 5.1V Zener diode

  17. Lecture #10 EGR 262 – Fundamental Circuits Lab Zener Regulator A Zener diode can be used to build a simple regulator circuit. It will regulate the voltage to the value of VZ, the Zener voltage. Discuss the operation of this regulator circuit. Add on a load resistor and calculate Vout for various values of RL using voltage division. Graph the results and identify the region where the Zener diode is regulating. About 20V with our transformers

  18. Lecture #10 EGR 262 – Fundamental Circuits Lab IC Regulators A wide variety of 3-terminal regulators are commercially available. The 7805 is a common 5V regulator. The 7805 will accept an input between 6V and 35V and deliver a constant 5V at the output. 3-terminal regulators are also available for 12V (7812) and other voltages, including variable regulators (such as the LM317). About 20V with our transformers

  19. 7805 + + 5V out 6 – 35V in _ _ 1 Vin 2 Vout + + LM317T 240W 3 (ADJ) Vin C2 1mF C1 0.1mF Vout 3 ADJ 2 Vout 1 Vin 5kW _ _ Lecture #10 EGR 262 – Fundamental Circuits Lab 7805 and LM317 Regulators

  20. Lecture #10 EGR 262 – Fundamental Circuits Lab 7.1. Pre-lab Tasks: (1) Sketch of power supply waveforms at node a, node b, node c (without the capacitor) and node c (with the capacitor) in Figure 6 (shown below). (2) Explain in your own words how your power supply works. (3) Schematic of the Zener diode regulator power supply, including the AC input, transformer, full-wave rectifier, filter capacitor, Zener-diode regulator (with 1kΩ resistor between filter capacitor and a 1N4733A (5.1V) Zener diode) and a load resistance. The load resistance should consist of a 100  resistor and a 10 kΩ potentiometer in series (to make sure that the load resistance never drops below 100 ). About 20V with our transformers + 100 F _ Figure 6: Full-wave rectifier

  21. Lecture #10 EGR 262 – Fundamental Circuits Lab 7.1. Pre-lab Tasks: (4) Calculate the predicted output voltage, Vout, of the Zener diode regulator if the unregulated voltage is 20V (not 12V as shown in the lab guide) and Rload = 100  , 200  , 300  , 400  , 500  , 1k, 2k, … , 10k. Show a sample calculation for Vout. Also calculate the power dissipated by Rload for each case and tabulate the results. What is the max power dissipation seen in this table? Graph Vout versus Rload. If the thumbwheel potentiometer used in lab has a max power rating of ¾ W, will the max rating be exceeded? (5) Schematic of 7805 regulator power supply, including the AC input, transformer, full-wave rectifier, filter capacitor, 7805, and a load resistance. The load resistance should consist of a 100  resistor and a 10 kΩ potentiometer in series. (6) Show the predicted output voltage, Vout, of the 7805 regulator if the unregulated voltage is 20V (not 12V as shown in the lab guide) and Rload = 100  , 200  , 300  , 400  , 500  , 1k, 2k, … , 10k. Explain how the predicted voltages were determined. Also calculate the power dissipated by Rload for each case. What is the max power dissipation seen in this table? Graph Vout versus Rload. If the thumbwheel potentiometer used in lab has a max power rating of ¾ W, will the max rating be exceeded?

  22. Lecture #10 EGR 262 – Fundamental Circuits Lab 7.2. In-lab Tasks: (1) Build the power supply circuit first without the voltage regulator and 100 μF capacitor. Use the oscilloscope to view the output of the transformer at node b. Use the Measurement feature on the oscilloscope to find the maximum voltage. Capture the image. (2) Use the oscilloscope to view the output of the full-wave rectifier at node c (with no capacitor). Use the Measurement feature on the oscilloscope to find the maximum voltage. Capture the image. (3) Measure the value of the capacitor (before adding it to your circuit) on an impedance bridge and record the value. (4) Now add the capacitor to your circuit and use the oscilloscope to view the voltage waveform at node c. Use the Measurement feature on the oscilloscope to find the average voltage and the ripple voltage. Capture the image. (5) Add the Zener-diode regulator circuit and 10 kΩ load resistor and measure the output voltage as a function of load resistance for Rload = 100  , 200  , 300  , 400  , 500  , 1k, 2k, … , 10k. (7) Remove the Zener-diode circuit and add the 7805 voltage regulator circuit and 10 kΩ load resistor and measure the output voltage as a function of load resistance for Rload = 100  , 200  , 300  , 400  , 500  , 1k, 2k, … , 10k.

  23. Lecture #10 EGR 262 – Fundamental Circuits Lab 7.3. Post-Lab Tasks: (1) Discuss the waveform captured showing the output of the transformer. Was it as expected? (2) Discuss the waveform captured showing the output of the full-wave rectifier without the filter capacitor. Was it as expected? (3) Discuss the waveform captured showing the output of the full-wave rectifier with the filter capacitor. Was it as expected? (4) Create a table comparing Vout (predicted) and Vout(measured) for each value of Rload for the Zener diode regulator circuit. Include % error. Also graph Vout (predicted) versus Rload and Vout(measured) versus Rload (on the same graph and include a legend). Discuss the results and explain any differences. (5) Create a table comparing Vout (predicted) and Vout(measured) for each value of Rload for the 7805 regulator circuit. Include % error. Also graph Vout (predicted) versus Rload and Vout(measured) versus Rload (on the same graph and include a legend). Discuss the results and explain any differences. (6) Compare the two power supplies built and tested in lab. Which is better? (7) The power supply you built provides 5 volts for your MicroStamp11. However, the op-amps used in Labs 6-7 require 9 volts. Explain how you could modify your power supply to power your op-amps.

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