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Low-Cost Laptop Automotive Adaptor

Low-Cost Laptop Automotive Adaptor. Thomas Dyer Solveigh Raske ECE 345 Senior Design Project TA: Mark Wiegert December 4, 2003. Motivation. Laptops batteries only last three hours Current in-store models are far too expensive for the average buyer Computers are needed while traveling

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Low-Cost Laptop Automotive Adaptor

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  1. Low-Cost Laptop Automotive Adaptor Thomas Dyer Solveigh Raske ECE 345 Senior Design Project TA: Mark Wiegert December 4, 2003

  2. Motivation • Laptops batteries only last three hours • Current in-store models are far too expensive for the average buyer • Computers are needed while traveling • Inexpensive CD player and cellular phone adaptors are already in stores

  3. Performance Requirements • Voltage input range from 10V to 20V dc • 20V dc 70W Maximum Output • +/-2% Output Voltage Ripple • Over-voltage protection to 75V spikes

  4. Design Requirements • Electrical Isolation • Low Cost • Robustness • Voltage Spike Protection • Reverse Polarity Protection

  5. Initial Block Diagram • Problem: Circuit would not turn on • Solution: Power PWM control from auto From Auto Isolation Control Reverse Polarity Protection Power Converter with isolation Spike Protection ToLaptop

  6. Final Block Diagram From Auto Isolation PWM Reverse Polarity Protection FlybackConverter Spike Protection ToLaptop

  7. Initial Schematic

  8. Initial Design Problems • No Load Regulation • Snubber Design/Placement • Slope Compensation • High Circuit Noise • Transformer Winding Window

  9. Final Schematic 4

  10. Part Choices • Switches • Snubber • PWM • Feedback Circuit • Transformer

  11. Transformer Design • 3 strand #20 gage wire windings • High-Voltage Insulating Tape • Soft Ferrite Core • (OP-44022-A240) • LI2 = 20mJ • Manufacturer’s Bobbin • E Core Geometry

  12. Endurance Tests • Short Circuit • High Ambient Temperature • Start-up in Cold Conditions • Reverse Polarity • Longevity

  13. Goals Attained • Output dc voltage is 20V • Load Regulation • Vout(no load) - Vout(full load) 20.54V – 19.58V 4.7% Vout(no load) 20.54V • Low-Cost • Line Regulation

  14. Line Regulation • Vout(highest input) - Vout(lowest input) Vout(nominal) 19.85V – 19.41V 2.2%20V

  15. Output Voltage • 1V peak-to-peak ripple • Ripple period is approximately 10µs • Average value of 20V T≈10us

  16. Efficiency • Efficiency at nominal voltage too low (63%) • Lower system Losses by: • Soft Switching • Mounting on PCB board • Reducing frequency

  17. Remaining Problems • Operates at 20W not at 70W • Voltage ripple is too high • Transformer producing audible noise • Efficiency too low

  18. Solutions • Using a different transformer • Higher turns ratio • Larger core • Larger effective winding area • Removing ground loops • Build on high density copper clad board • Better common mode filter into op-amp

  19. Transformer Redesign I • Calculations (L = 100uH) • Pout = 70 W Assume=0.6 efficiency • Pin = 117W Imax in = 11.7A+10% = 13.4 A • Imax out = 3.5A+10% = 3.85 Itot = 16.7 A • LI2 = 28mJ The smallest core that meets this requirement is the 45528-A400 which has a nominal winding area of 0.438in2

  20. Transformer Design II • N2 =100000/400 so Nmin pri = 16 turns • For a dmax = 0.5 Vouttran Nout so Nout = 38 turns Vin min Nin Total number of turns is 54

  21. Cost Analysis I

  22. Cost Analysis II • Total Cost $14.78 • Laptop Adaptor at Circuit City is $80.00

  23. Questions?

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