Wireless Charging System for Mobile Phones - Electronic Engineering Guide
1. Introduction
Wireless charging is a technology that allows the transfer of power without physical connectors using inductive coupling. This guide outlines how to build a wireless charging system suitable for mobile phones, focusing on the electronic design aspects.
2. Objectives
• Develop a basic wireless charging system using inductive
coils.
• Design both transmitter and receiver circuits.
• Ensure efficient energy transfer with minimal losses.
• Maintain safety and voltage regulation for mobile charging.
3. Components Required
• Transmitter Coil (Copper wire wound into a flat spiral)
• Receiver Coil (matching or similar design)
• High-frequency Oscillator Circuit (555 Timer or inverter circuit)
• MOSFETs or BJTs (for signal amplification)
• Capacitors and Inductors (LC tuning circuit)
• Voltage Regulator (e.g., LM7805, AMS1117)
• Bridge Rectifier (Schottky diodes for better efficiency)
• Microcontroller (optional – for advanced monitoring)
• Mobile Phone with Qi-compatible receiver (for testing)
4. Working Principle
The system operates on the principle of electromagnetic induction. An alternating current is passed through the transmitter coil, generating a magnetic field. When a receiver coil (in the phone) is brought near the transmitter, the magnetic field induces a voltage in the receiver coil, which is then rectified and used to charge the phone battery.
5. Transmitter Circuit Design
• Generate high-frequency AC using an oscillator circuit
(typically 100 kHz to 200 kHz).
• Drive the transmitter coil using MOSFETs in a push-pull or class D
configuration.
• Match the coil and capacitor values for resonance to increase efficiency.
• Use a stable power supply (9V–12V recommended).
6. Receiver Circuit Design
• The receiver coil captures the AC signal.
• Use a full-bridge rectifier to convert AC to DC.
• Filter the output using capacitors.
• Use a low-dropout voltage regulator to produce 5V USB-compatible output for
mobile charging.
7. Microcontroller Integration (Optional)
• Use microcontroller to monitor voltage, temperature, and
current.
• Add display or Bluetooth module to transmit charge data.
• Implement smart charging cutoff or fault detection mechanisms.
8. Power Management and Regulation
• Ensure output voltage is safe (usually 5V for USB
charging).
• Protect circuits from over-voltage and over-current using Zener diodes or
fuse.
• Monitor coil temperature to avoid overheating.
9. Safety and Efficiency Considerations
• Keep coil distance under 10mm for best results.
• Shield circuits to prevent EMI interference.
• Use ferrite core to focus the magnetic field.
• Use quality components to reduce energy losses.
10. Applications
• Wireless charging pads for smartphones
• Wearable device charging stations
• Electric toothbrush chargers
• Smart desks and furniture integration
11. Limitations and Future Enhancements
• Charging speed is slower than wired connections.
• Energy loss due to heat and distance.
• Future work: multi-device charging, smart alignment, Qi certification, fast
charging compatibility.
12. Conclusion
Wireless charging technology simplifies the user experience and increases device lifespan by reducing mechanical wear. This guide provides a foundational electronic design approach for building a reliable wireless charger for mobile phones.