This document describes a student project to design a wireless phone charging system using magnetic induction that complies with the Qi wireless charging standard. The system includes a transmitter unit containing a step-down transformer, half-bridge inverter, and resonant circuit to transmit power, and a receiver unit containing a resonant circuit, rectifier, and voltage regulator to receive power and charge a phone. The goals are to wirelessly transfer around 5W of power and establish communication between the transmitter and receiver units.

1. Wireless Power Charging System
Through Magnetic Induction
Tamim Alkhonaini
UBong Udoessien
Nadeem Qandeel
Advisor: Dr. Aiping Yao | Committee: Dr. Michael Glazos, Dr. Mark Petzold

2. Outline
1. Background
2. Problem Statement
3. Goals
4. Project Description
5. Modifications
6. Test/ Verification
7. Problems
8. Future Work
9. Budget
10.Conclusion

3. Background
1. Wireless energy transfer since 1800’s.
2. Interest in new applications for consumer products.
3. Applications could extend to higher power, e.g. electric
vehicles.
4. Industry standard which all products conform to.
5. Wireless Power Consortium; Qi Standard.
6. Different devices will charge with each others wireless
charging device.

4. Problem Statement
Design and implement a wireless phone charging
system, in compliance with Qi standard, that will
transfer around 5W of power to a mobile device,
using inductive coupling.

5. Goals
• First semester
1. Charge a mobile phone wirelessly through inductive coupling.
2. Using transmitter unit, reciever unit and Arduino.
3. Connect LCD and weight sensor.
• Second semester
1. Establish communication between receiver and transmitter.
2. Ensure a 80% power transfer efficiency.
3. Base station will charge multiple mobile devices simultaneously.

6. Project Description
● Transmitter Unit (Base station).
● Receiver Unit.
● Control/ Communication Unit.

7. Project Description: Transmitter Unit
● Step Down Transformer
○ 240V/12v
● Half Bridge Inverter: Converts DC to AC
○ 12V VDD
○ 5V, (110 KHz - 205 Khz), 50% Duty Cycle
○ 2N7002 Mosfets (2)
● Resonant Circuit: Converts AC square wave to sinusoidal wave
○ Primary Coil (12.5uH)
○ Capacitor (0.147uC)

8. Project Description: Transmitter Unit
LTSpice Simulation of Transmitter circuit.

9. Project Description: Receiver Unit
The receiver unit is responsible
for picking up AC signal from
the transmitter unit using
secondary coils, and then
convert it to DC voltage to
charge the phone.

10. Project Description: Receiver Unit
Receiver unit consists of:
● Resonant Circuit: AC filter. ( L = 16 uH, Cs=127 nF, Cd= 1.6 nF)
● Full bridge rectifier: convert from AC to DC. (Four 1N4148 diodes)
● Low-pass filtering capacitance: 22uF
● voltage regulator: regulate voltage to 5 V. (LM7805C)

11. Project Description: Control /Communication Unit
Arduino Uno
● Control switching frequency of system using PWM.
● Control LCD output.
● Receives input from weight sensor.
Communication
● Send instructions from receiver to transmitter regarding:
o Start and stop charging.
o Amount of power supplied.

12. Modifications
● Transmitter circuit
○ Use of half Bridge Inverter
○ Half bridge Driver IC to maximize switching speed.
● Receiver circuit
○ Add resonant capacitor to have a stronger signal which will increase
the efficiency.
● Communication and Control
○ NFC as an alternative to Bluetooth.
○ Automatic connection (No Pairing).
○ Tag doesn't require Power.
○ 2 PWM’s instead of 4.
○ Use less than 4 buttons for LCD.

13. Test/Verification
Generation of PWM signal
● Desired frequency range 100 KHz - 200 KHz
(recommended 125 KHz)
● Duty cycle range (0%<d<100%)
● Amplitude 4. 7 V
● Noise 0.5-0.9 %

14. Test/Verification.
Weight Sensor
● Sensitivity 10 g - 1 Kg
● Active area 4cm x 4cm

15. Test/Verification
LCD
● Display phone information.
LED’s
● Light indicators

16. Test/Verification
Testing Results (Receiver unit):
A phone was tested while it is charging to measure the exact charging voltage
and current.
● Phone type: iphone 4s
● Voltage: 4.75 V
● Current: 0.77 A
● Power: 3.66 W

17. Test/Verification
The Receiver circuit was designed and simulated by using
LTspice.

18. Test/Verification
LED experiment was done to test the magnetic induction
between primary and secondary coils.
● Using a function generator, the primary coil was supplied by: 120 KHz sine
wave, 8 Vpp.
● 120 KHz → weak light , 230 KHz → strong light.

19. Test/Verification
Transmitter unit:
● Load Voltage: 2.4V,50% Duty cycle, 110 Khz.
● Load current: 0.16A.
● Load Resistor: 15 Ohms.
● Dimly lit LED, No coupling.

20. Problems
Transmitter Unit
The ultimate goal of the Tx circuit is to achieve a high voltage and low current.
Expected Outputs: 6V, 0.4A
Experimental Outputs: 2.4V at 50% duty cycle.
● Cross Conduction
● Slow switching due to CMOS inverter low current.
Some Problems.
Possible Solutions.
● Use a half-bridge driver ic.

21. Problems
Receiver Unit:
The goal of the receiver circuit is to charge a phone.
Expected Outputs: 4.8 V, 0.8 A
Experimental Outputs: 4.70 V, 0.047 A
● output current is very low <0.05 A
● Secondary coil can not pick up a signal from transmitter unit.
Some Problems:
Possible Solutions:
● Use a transistor as a current
amplifier.

22. Future Work
● Addition of NFC Reader and Tag to transmitter and
receiver unit respectively.
● Improve circuitry for both transmitter and receiver.
● Use PWM generated from UNO to run transmitter
circuit.
● Producing a document comparing research and
findings.

23. Future Work
• First semester modified
schedule.
• Second semester plan of
work.
Task Start Date Duration (Days) End Date
First Semester
Research 1/12/2015 34 2/15/2015
Proposal 1/20/2015 31 2/20/2015
Shopping 3/15/2015 15 4/1/2015
Design & Simulation 2/28/2015 5 3/5/2015
Parts Testing 3/3/2015 7 3/10/2015
Transmitter Testing 3/20/2015 30 4/19/2015
Receiver Testing 3/20/2015 30 4/19/2015
Arduino Testing 3/23/2015 23 4/15/2015
Transmitter & Receiver 4/20/2015 6 4/26/2015
Progress Report 4/21/2015 14 5/5/2015
Hardware Demo 4/27/2015 4 5/1/2015
Second Semester
Transmitter & Receiver 9/5/2015 20 9/25/2015
Communication 9/15/2015 30 10/15/2015
Evaluation 10/20/2015 5 10/25/2015
Improvements 10/25/2015 31 11/25/2015
Final Hardware Demo 12/7/2015 3 12/10/2015
Final Report 11/20/2015 26 12/16/2015

24. Future Work
GANTT Chart for both 1st and 2nd semester
1/12 2/1 2/21 3/13 4/2 4/22 5/12 6/1 6/21 7/11 7/31 8/20 9/9 9/2910/1911/811/2812/18 1/7
Research
Shopping
Parts Testing
Receiver Testing
Transmitter & Receiver
Hardware Demo
Transmitter & Receiver
Evaluation
Final Hardware Demo

25. Budget
item Price per
Unit
Number of
units
Total price
LCD Display
Board
$ 20.00 1 $ 20.00
Transmitter Coils $ 10.00 1 $ 10.00
Receiver Coils $ 8.00 1 $ 8.00
Arduino $ 30.00 1 $ 30.00
Bluetooth Module $ 35.00 1 $ 35.00
Sensor $ 4.00 1 $ 4.00
USB breakout $ 10.00 1 $ 10.00
Shipping $ 30.00
1st semester total cost is $ 147.00
item Price per
unit
Number
of units
Total price
Sensors $ 4.00 3 $ 12.00
Transmitter
Coils
$ 10.00 3 $ 30.00
Receiver
Coils
$ 8.00 1 $ 8.00
Shipping $ 30.00
2nd semester total cost is $ 80.00

26. What’s learned!
Based on research, simulation and experimentaion we
learned about power conversion, system integration and
requirements for wireless charging in mobile devices.

27. Conclusion
Modifications to the project based on new information
about Qi standard and problems encountered, will lead to
improvements in the design and circuitry of the project.
This will allow for efficient power transfer and
communication between the base station and a mobile
device.