1. Design, Implementation and Validation of a USB Charger Ilia Baranov Department of Electrical and Computer Engineering University of Waterloo 2A Candidate for B.A.Sc. in Electrical Engineering January 26 th, 2010 Copyright © 2010 by Ilia Baranov. All rights reserved. TPPE 000 Technical Presentation Proficiency Examination

2. Design, Implementation and Validation of a USB Charger 2 Outline Background Conception –Problem, available solutions, and requirements Design –Discharging circuit –Batteries –Charging circuit Implementation Validation and demonstration Next Steps Summary

3. Design, Implementation and Validation of a USB Charger 3 Self designed USB power source Can be used to charge any device with a USB interface Provides power on the go Background

4. Design, Implementation and Validation of a USB Charger 4 Conception

5. Design, Implementation and Validation of a USB Charger 5 Problem Lots of USB powered devices + Very little USB infrastructure = Many chargers and adapters Idea –Portable USB power source –3 main components, storage, charging, discharging http://marylandmedia.com/2009/01/a-free-idea-usb-wall-outlet/ Problem

6. Design, Implementation and Validation of a USB Charger 6 Available Solutions POWERSTICK™ Duracell Powerhouse –$50 - $70 –750mAh – 2000mAh –Pocket sized –Simple to use MintyBoost kit, similar to my project, yet has no charging [1] –$40, assembly required www.Powerstick.com http://www.ohgizmo.com/

7. Design, Implementation and Validation of a USB Charger 7 Requirements 1.Cost 2.Size 3.Complexity 4.Usability 5.Storage 6.Amperage 7.Longevity 8.Tooling Time $10 - $35 20% HIGHCost Handheld 6% LOWSize < 30 parts 5% LOWComplexity Simple 12% HIGHUsability RangeQuantitative Weight Qualitative Weight Criteria > 1500 mAh 18% HIGHStorage >= 600 mA 12% MEDIUMAmperage > 2 months 18% HIGHLongevity < 1 week 9% LOWTooling Time 100% Sum Table 1. Requirements Weightings

8. Design, Implementation and Validation of a USB Charger 8 Design

9. Design, Implementation and Validation of a USB Charger 9 Discharging circuit Requires: –2-4 V to 5 V conversion –At least 600mA –Simplicity Lt1308b is chosen [3] lt1308b.pdf

10. Design, Implementation and Validation of a USB Charger 10 Batteries Requires: –Rechargeable –High capacity –2-4V –Long shelf life Chose NiMH over Li-ion: –Solder two low self-discharge AA NiMH batteries –2000mAh –Very long self life tradevv.com

11. Design, Implementation and Validation of a USB Charger 11 Charging circuit Must charge two AA from a USB port –Must be simple yet robust Solution: a voltage comparator checks a thermo-resistor LM393 dual voltage comparator www.stefanv.com/electronics/usb_charger.html V tmp > V ref V tmp < V ref

12. Design, Implementation and Validation of a USB Charger 12 Implementation

13. Design, Implementation and Validation of a USB Charger 13 The Circuit

14. Design, Implementation and Validation of a USB Charger 14 Physical Assembly

15. Design, Implementation and Validation of a USB Charger 15 Validation

16. Design, Implementation and Validation of a USB Charger 16 Price List

17. Design, Implementation and Validation of a USB Charger 17 Demonstration

18. Design, Implementation and Validation of a USB Charger 18 Goals achieved? Final Value RangeCriteria Table 2. Requirements Review > 2 months Longevity >> 2 months $10 - $35 Cost $21 Handheld Size Handheld < 30 parts Complexity 24 parts Simple Usability Simple > 1500 mAh Storage > 2000 mAh >= 600 mA Amperage = 600 mA < 1 week Tooling Time 4 days

19. Design, Implementation and Validation of a USB Charger 19 Next Steps Smaller size More advanced charging circuitry PCB (Printed Circuit Board ) with SMD (Surface Mounted Device) components More batteries to be more efficient

20. Design, Implementation and Validation of a USB Charger 20 Summary Portable USB power source Uses low self-discharge NiMH for storage Voltage comparator for charging Lt1308b for discharging Cheaper and more effective than what is available Plans to move ahead with next version

21. Design, Implementation and Validation of a USB Charger 21 References [1]Lady Ada, “Minty Boost”, Adafruit Industries, 2009-11-12; http://www.ladyada.net/make/mintyboost/. [2]Stefan Vorkoetter, “Build a USB Powered AA NiMH and NiCd Battery Charger”, Stefanv.com, 2009-11-14; http://www.stefanv.com/electronics/usb_charger.html/. [3]Lt1308b, High Current, Micropower, Single Cell, 600kHz, DC/DC Converters., Milpitas, Ca: Linear Technology, 1999, pp. 1 – 20. Questions?