EE302 Lab 8 Buck Converter

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Electrical Engineering

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Jan 9, 2024

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EE302 Lab 8: Buck Converter Final Project Obtain: Download Libraries.zip from Canvas or Discord Motivation: The final project for EE 302 will be to build a power converter, i.e. an electrical circuit that can provide a desired voltage to a load while receiving a different voltage from a power source. (An example would be a circuit that converts the 110 Vrms sinusoidal voltage of the grid to the 19 Vdc that is compatible to input to your laptop). In particular, we will build a buck converter, which produces a lower output voltage than its input voltage. We already know some ways to reduce voltages (resistor dividers; certain amplifier configurations), but these are all lossy circuits, meaning that they dissipate power. Power converters, by contrast, are theoretically 100% efficient and, in practice, regularly achieve efficiencies of 90+%. Lab: 1. Recreate the circuit below in the KiCad schematic editor (for components not natively in KiCad, see step 2):

2. You will need some components that are not natively in KiCad. Follow the following instructions to import them: a. Download and extract the files into a directory of your choice. b. Open KiCad, go to Schematic Editor and click on Preferences > Manage Symbol Libraries. Make sure you are on the "Global Libraries" tab. Browse to the bottom of the table, then click on the “+” icon followed by the “folder” icon. Browse to the location of “BuckParts.kicad_sym” and click “OK” c. Go to PCB Editor and click on Preferences > Manage Footprint Libraries. Make sure you are on the "Global Libraries" tab. Browse to the bottom of the table, then click on the “+” icon followed by the “folder” icon. Browse to the location of “BuckParts.pretty” and click “OK” (Note that symbol libraries like BuckParts.kicad_sym are files , while footprint libraries are folders such as BuckParts.pretty) OR d. If you would like to use the default KiCad directory and have these libraries available for all your projects, then first navigate to the default location for KiCad symbols (which should be something like C:\Program Files\KiCad\share\kicad) e. Go into the "symbols" directory and paste "BuckParts.kicad_sym" there f. Go into "footprints" directory and paste "BuckParts.pretty" there

3. Associate the each component with a footprint according to the following chart: R (except current sense resistor R1) Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal R1 (current sense resistor) Resistor_THT:R_Axial_DIN0922_L20.0mm_D9.0mm_P30.48mm_Horizontal Capacitors Capacitor_THT:C_Disc_D3.8mm_W2.6mm_P2.50mm Terminal Blocks Connector_Phoenix_MSTB:PhoenixContact_MSTBA_2,5_2-G_1x02_P5.00mm_Horizontal Test Points TestPoint:TestPoint_Keystone_5010-5014_Multipurpose Coaxial Connector Connector_Coaxial:BNC_Amphenol_B6252HB-NPP3G-50_Horizontal MOSFET Package_TO_SOT_THT:TO-220-3_Vertical L SamacSys_Parts:7447231101 (imported) TPS2832D Gate Driver Package_SO:SO-8_3.9x4.9mm_P1.27mm TLV2372 Dual Op Amp Package_SO:SO-8_3.9x4.9mm_P1.27mm 4. Transfer your design to a PCB and begin laying out components. Please review Lab 2 to remember how to do this. As a reminder from Lab 2, there are several good recommendations and rules of thumb you might follow:  First arrange your components and imagine how the connections will be made. Only start drawing connections when you’re satisfied with the component positions.  Place connectors around the outer edge of the board, not the inner area  Place test points around the outer edge of the board, not the inner area. Space them far enough from other tall components (connectors) and each other that you can easily probe multiple test points without the probes interfering with each other  It’s usually valuable to aim for high component density. However, this only applies to the circuit itself, not to the connectors and test points! Therefore, you may end up with a dense circuit in the middle of your PCB with substantial “white space” around it. That’s okay – boards that are too small do not sit stably on the bench and make external connections more difficult.  Do not try to lay out your circuit to look like the schematic. Instead, try to lay out components in a way that makes connecting them as easy as possible. As you advance in your understanding of EE, you will make layout decisions based more and more on electromagnetic and thermal considerations than on convenience.  This board includes several capacitors, known as a “bypass capacitors.” We’ll study the purpose of this later in the course. For now, you should simply internalize the rule that every IC should have a bypass capacitor across its power pins and as close as possible to the IC . The the switching loop (the loop that involves a capacitor and the two MOSFETs) should be made as tight as possible.  Depending on the product you’re building, don’t be afraid to place components on both sides of the board. When components overlap, however, do think about how you will solder the components in – you don’t want to solder one component and cover access to another component’s pads.

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