1. CTU: EE 375 – Electronics 1: Lab 1: Regulated DC Power Supply 1 Colorado Technical University EE 375 – Electronics 1 Lab 1: Regulated DC Power Supply February 2010 L. Schwappach and C. Fresh ABSTRACT: This lab report was completed as a course requirement to obtain full course credit in EE375, Electronics 1 atColorado Technical University. This lab report investigates the design and implementation of a DC Power Supply. Hand calculationsare developed using the properties of Diodes and then verified using P-Spice schematic calculations to determine the viability of designprior to a physical build of the design. P-Spice simulation results and hand calculations are then verified by physically modeling thedesign on a bread board and taking measurements for observation. The results are then verified by the course instructor. The resultsof this Lab illustrate the performance of a DC power supply built using discrete diodes as a bridge rectifier, a filter capacitor, andfinally a 10V Zener diode used as an output shunt voltage regulator. If you have any questions or concerns in regards to this laboratory assignment, this laboratory report, the process used indesigning the indicated circuitry, or the final conclusions and recommendations derived, please send an email toLSchwappach@yahoo.com or Cfresh24@comcast.net. All computer drawn figures and pictures used in this report are of original andauthentic content. The authors authorize the use of any and all content included in this report for academic use. zone acts as an insulator, preventing any significant electric current flow. However, if the polarity of the external voltage I. INTRODUCTION opposes the built-in potential, recombination can once again proceed, resulting in substantial electric current through the p- DC power supplies are necessary to run many of today’s appliances. Diodes are important n junction. For silicon diodes, the built-in potential isbasic components of these power supplies, both forrectification in the original AC power supply and in regulation approximately 0.6 to 0.7 V. Thus, if an external current isof the output voltage. This lab assignment uses a simple AC passed through the diode, about 0.6 to 0.7 V will be developedtransformer; a bridge rectifier, a filter capacitor, and finally a across the diode and the diode is said to be “turned on” as itZener diode to build a regulated DC power supply. has a forward bias. In this lab the forward bias diode potential is approximately 0.7V. II. OBJECTIVES The I-V characteristic of an ideal diode is: The objective of this lab is to study the design andperformance of this simple DC power supply at each stage. Where I is the diode current, Is is the reverse bias saturationFirst the design is built with discrete diodes and integrated current, VD is the voltage across the diode, VT is the thermalbridge rectifier. Next, a RC filter (with a ripple less than 10% voltage (Approximately 25.85 mV at 300K), and n is theof Vm) is added to the design and output ripple measurements emission coefficient, also known as the ideality factor.are taken. Finally, a Zener Diode and resister are added and Zener Diodes are diodes that can be made to conductthe output shunt voltage performance is measured. backwards. This effect, called breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference or output shunt voltage regulator III. DIODE THEORY as which is demonstrated by this lab. Some of the equations needed to perform circuit A diode is a two-terminal electronic component that calculations used when including Zener diodes are:conducts electric current in only one direction. Thisunidirectional behavior is called rectification, and is used toconvert alternating current to direct current, and removemodulation from radio signals in radio receivers. Specialtypes of Diodes are used to regulate voltage (Zener diodes),electronically tune radio and TV receivers (varactor diodes),generate radio frequency oscillations (tunnel diodes), andproduce light (light emitting diodes). Today most diodes are made of silicon, but othersemiconductors such as germanium are sometimes used. If an external voltage is placed across the diode withthe same polarity as the built-in potential, the diodes depletion
2. CTU: EE 375 – Electronics 1: Lab 1: Regulated DC Power Supply 2 V. HAND CALCULATIONS A diode bridge is an arrangement of four diodes in a The following hand calculations below build a DCbridge configuration (see PSpice diagram for an illustration) power supply into three phases. In phase 1 the circuit isthat provides the same polarity of output for either polarity of constructed using the transformer, a bridge rectifier and a loadinput. The most common application of a diode bridge is used resister. In the second phase the Circuit is expanded tofor conversion of an alternating current input into direct include a filter capacitor which drastically lowers the “ripple”current a direct current output. This configuration is known as of the bridge rectifier. In the final phase a Zener diode isa bridge rectifier. added to the design demonstrating the voltage shunting ability For many applications, especially with single phase of the Zener in limiting the output voltage so long as the ZenerAC where the full-wave bridge serves to convert an AC input diodes power rating is not exceeded. The hand calculationsinto a DC output, the addition of a capacitor (this labs filter below illustrate each stage.capacitor) may be desired because the bridge alone supplies anoutput of fixed polarity but continuously varying or"pulsating" magnitude, an attribute commonly referred to as"ripple". This filter capacitor lessons the variation, orsmooth’s the rectified AC output from the bridge. The equation needed to calculate the ripple voltageafter including the capacitor in the lab design is: A rectifier is an electrical device that convertsalternating current to direct current, a process known asrectification. A full-wave rectifier converts the whole of theinput waveform to one of constant polarity (positive ornegative) at its output. Full-wave rectification is achievedusing four diodes in a configuration known as a bridge andconverts both polarities of the input waveform to a singlepolarity direct current. Figure 1: Hand Calculations for Part 1 (Design using transformer and bridge rectifier). See attachments section for full size image. IV. DESIGN APPROACHES/TRADE-OFFS This lab was built upon three design approaches.First the lab approached the design using only the transformerand four diodes as a bridge rectifier and a single resister toprovide a load. Although the trade-offs in this design allowedfor rectification of the AC signal to a DC signal, there was nosignal smoothing nor could the output be shunted to a specificconstant voltage. This made the design impractical for use asa steady DC power supply. The second lab design included the previous designwith a capacitor to filter out the pulsating ripple of after thebridge rectifier. The trade-offs in this design allowed for asmoother output with the additional cost of a capacitor as theonly drawback. The third lab design included the previous designswith an added resistor and Zener diode which acted as anoutput shunt voltage regulator, limiting the direct currentvoltage to a constant linear voltage. The advantage to thisdesign is a constant direct current output which is essential totoday’s electronics with only the cost of an extra diode andsmall resistor.
3. CTU: EE 375 – Electronics 1: Lab 1: Regulated DC Power Supply 3 VI. CIRCUIT SCHEMATICS The circuit schematics below were built in PSpice and allowed our team to analyze the circuit digitally before performing the physical build. Figure 4: PSpice Schematic of Design 1 (Part 1). See attachments section for full size image.Figure 2: Hand Calculations for Part 2 (Design using Part 1 Design with addition of filter capacitor). See attachments section for full size image. Figure 5: PSpice Schematic of Design 2 (Part 2), RL=1k. See attachments section for full size image. Figure 6: PSpice Schematic of Design 2 (Part 2) RL=10k. See attachments section for full size image.Figure 3: Hand Calculations for Part 3 (Design using Part2 Design with addition of Zener Diode). See attachments section for full size image. Figure 7: PSpice Schematic of Design 2 (Part 2) RL=100. See attachments section for full size image.
4. CTU: EE 375 – Electronics 1: Lab 1: Regulated DC Power Supply 4 capacitance. A oscilloscope for viewing the input and output waveforms of the circuit. A power supply/transformer capable of converting a 110(rms)V @ 60Hz to 12.6(rms)V. A 423.75Ω(220+220) resistor for Ri, and 200Ω (200.2), and 1kΩ (1.05k), 10kΩ (9.98k), 150kΩ(149.5k) resistors for testing RL. A 83.33µF (100) Bread board with wires. Figure 8: PSpice Schematic of Design 3 (Part 3) RL=1k. NOTE: Resistors can normally provide around +/- See attachments section for full size image. 5%-25% difference between actual and designed values while Capacitors generally provide around 20%-50% difference between actual and designed values. You can add resisters in series as (R1+R2) to closer approximate required resistance values and you can add Capacitors in parallel as (C1+C2) to closely approximate required capacitance. VIII. PSPICE SIMULATION RESULTS Figure 9: PSpice Schematic of Design 3 (Part 3) RL=10k. See attachments section for full size image. Figure 12: PSpice Simulation Results of Design 1 (Part 1) Figure 10: PSpice Schematic of Design 3 (Part 3) RL=1k and 10k. See attachments section for full size RL=150k. See attachments section for full size image. image.Figure 11: PSpice Schematic of Design 3 (Part 3) RL=200. See attachments section for full size image. VII. COMPONENT LIST The following is a list of components that were used inbuilding the final DC power supply. (The actual values our Figure 13: PSpice Simulation Results ofgroup used in the build are in parenthesis). Design 2 (Part 2) RL=1k. See attachments A digital multimeter for measuring circuit section for full size image. voltages, resistor resistances, and capacitor
5. CTU: EE 375 – Electronics 1: Lab 1: Regulated DC Power Supply 5 Figure 14: PSpice Simulation Results of Figure 17: PSpice Simulation Results of Design 2 (Part 2) RL=10k. See attachments Design 3 (Part 3) RL=10k. See attachments section for full size image. section for full size image. Figure 15: PSpice Simulation Results of Design 2 (Part 2) RL=100. See attachments Figure 18: PSpice Simulation Results of section for full size image. Design 3 (Part 3) RL=150k. See attachments section for full size image. Figure 16: PSpice Simulation Results of Design 3 (Part 3) RL=1k. See attachments section for full size image. Figure 19: PSpice Simulation Results of Design 3 (Part 3) RL=200. See attachments section for full size image.
6. CTU: EE 375 – Electronics 1: Lab 1: Regulated DC Power Supply 6 IX. EXPERIMENTAL DATA produced a greater “ripple” than was allowed by the initial design constraints. However we also observed that the higher The following table illustrates the measurements the value of RL the less “ripple” observed.taken at each stage of the lab. Stage 3: After adding the Zener diode the ripple in our filter rectifier remained constant regardless of whether we used a STAGE 1: Bridge (10k, or 1k resistor). This is most likely due to the voltage Rectifier limiting characteristics of the Zener diode. The V ripple was RL (Actual) VL (Actual) exactly the same “ripple” we achieved from the previous design. 10k (9.98k) 0V to 16.419V After adding the Zener diode, RL produced a 1k (1.05k) 0V to 16.419V constant voltage of approximately 10V. This was true for the 1k, 10k, and 150k resistors. However the 200 ohm resistor 100 (99.2) 0V to 16.419V pushed the Zener diode outside of its Power limitation of .5WTable 1: Stage 1: circuit measurements (Rectifier without producing unstable results at 4.97V. Again all measurements Filter Capacitor) observed were within 10% of Hand and PSpice calculated results. STAGE 2: Includes XI. CONCLUSIONS Filter Capaciter This lab was effective in demonstrating the AC to DC RL (Actual) VL (Actual) rectification capabilities produced by using a bridge rectifier 10k (9.98k) .2V and the power of diodes in restricting current in one direction. Through adding the filter capacitor in phase 2 our team 1k (1.05k) 2.2V observed the how the “ripple” could be smoothed and reduced Table 2: Stage 2: circuit measurements (Rectifier with to exact specifications. Finally in phase 3 after designing the Filter Capacitor) Zener Diode we observed the voltage shunting capabilities of such a diode and observed the importance of choosing a value STAGE 2: Includes of Ri that would allow for lower load impedances in your Filter Capaciter design. This lab was incredibly effective in providing a visual look at diodes and their usefulness in power supplies and RL (Actual) VL (Actual) circuit design. 10k (9.98k) 9.99V XII. ATTACHMENTS 1k (1.05k) 9.983V All figures above follow. 150k (149.5) 10.004V 200 (200.2) 4.97 REFERENCES Table 3: Stage 3: circuit measurements (with Stage 2 and  D. A. Neamen, “Microelectronics: circuit analysis and design - 3rd ed.” added Zener diode.) McGraw-Hill, New York, NY, 2007. pp. 1-107. X. ANALYSIS Stage 1: In design 1 the bridge rectifier efficiently producedan expected DC voltage, however the was a tremendous“ripple” that would not have been good for using the Powersupply as a stable power supply. Stage 2: After adding the filter capacitor the output rippleclosely approximated hand and PSpice calculations within10%. The output ripple was also smoothed and greatlyreduced by the capacitor producing a more stable DC output.Our physical calculations, hand and PSpice calculations againwere within 10% proving the validity of our design. Since our filter capacitor was designed using a worstcase scenario of a 1k resister at RL, changing RL below 1k