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Wireless power for mobile phones - System overview. Nov 25, 2012 V1.1. System overview. Embedded in mobile device After market case/dongle connected through the power connector Add-on connected through dedicated WLC pins. Rx. Tx. Embedded in furniture/car/infrastructure

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Wireless power for mobile phones - System overview

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Wireless power for mobile phones -

System overview

Nov 25, 2012

V1.1


System overview

  • Embedded in mobile device

  • After market case/dongle connected through the power connector

  • Add-on connected through dedicated WLC pins

Rx

Tx

  • Embedded in furniture/car/infrastructure

  • After market mat


Block diagram

Power Source

Communication

Power

Resonance circuit & power driver

TXCoil

RXCoil

Matching circuit & Rectifier

Control

Unit

Control

Unit

Demodulator

Modulator

DC/DC


Tx-Rx coils


Tx-Rx coils – Magnetic induction basics

Electric current flowing in a wire gives rise to a magnetic field around it.

Alternating the current will alternate the magnetic field

Shaping the wire as a loop will band that field in a “lung” shape.

Figures: http://ipodphysics.com/magnets-loop-or-coil.phpt


Tx-Rx coils – Magnetic induction basics

Energy coupling means that an energy source has a mean of transferring its energy to a second object. Transformers may use iron core to deliver the magnetic flux

Wireless power system is an air core transformer between planar coils one on top of the other.

Figure 1: http://www.electrical4u.com/what-is-transformer-definition-working-principle-of-transformer/ Figure 2: http://makezine.com/2013/11/04/component-of-the-month-transformer/ Figure 3: http://www.britannica.com/EBchecked/media/1355/Magnetic-field-B-of-two-current-loops-with-currents-in


Tx-Rx coils – Coil designs

Single coil– Most common design

Pros – chip and easy solution / Cons – difficult alignment

Large Tx coil – Common in loosely coupled systems

Pros – easy alignment / Cons – difficult design and tune

Array of small Tx coil – One or more coils provide power simultaneously

Pros – easy alignment / Cons – Cost of coils and drivers

3 coil array – Only one coil provides power at a time

Pros – easy alignment / Cons – Cost of coils and drivers

Fig1:http://www.qitah.com/blog.htmlFig2:http://phys.org/news203691107.htmlFig3:http://patentimages.storage.googleapis.com/US20130119773A1/US20130119773A1-20130516-D00015.png


Resonancecircuit and power driver


Resonancecircuit and power driver

Power driver

Resonance circuit

Resonant circuit - Determines the self resonance frequency of the Tx,

Mainly influenced by the coil and the resonance capacitors.

Power driver - pushes the current to the resonance circuit in different frequencies around the self resonance

Figure 1: HIGH EFFICIENCY LOOSELY COUPLED WIRELESS POWER TRANSFER SYSTEM VIA MAGNETIC INDUCTION By ZHEN NING LOW


Resonancecircuit

  • The overall impedance the driver “sees” when modeled as a series RLC circuit

  • At the resonance frequency the capacitive and inductive impedance equals

  • The driver then sees resistive only minimum overall impedance and the power

  • delivery to the Rx is maximal

  • The resonance curve changes with each different :

    • Rx design (EE & ME)

    • Phone material

    • Misalignment from the center

    • Variation during manufacturing

    • Load drawn

Amplitude

Frequency

Figure 1: http://perlgeek.de/blog-en/perl-6/rakudo-memory-leaks.html


Driving the power

  • Frequency control – the driver changes the frequency along the resonance curve

    • Control becomes difficult when Q is high & at resonance control is unstable

    • Frequency range shall be dynamic due to curve changes

    • Passing to the second side of the peak may reverse the control rules

Amplitude

Frequency

Other methods of control:

Voltage control – increasing the input voltage will increase the current through the coil and the transmitted power

Pulse width control – increasing the on time of the signal will increase the transmitted power


Data modulation


Data modulation

Power driver

Matching circuit & Rectifier

Modulator

  • load modulation -

  • Rx modulates the operational frequency by short circuiting the coil to a secondary load

  • The secondary load changes both the load of the Tx and the resonance curve

  • The demodulator sense the change in voltage, current or phase between them on the operational frequency

Demodulator


Data modulation

Example of voltage change at the Tx

Example of phase change at the Tx

Signals in reality may vary a lot from the simulation presented….


Questions? Comments? Remarks?

It’s called wireless power, it’s the future

Thanks,

Rotem Shraga

(shraga.rotem@gmail.com ; 052-6443944)

Figure: http://www.fodrizzle.com/wp-content/uploads/2012/02/funny-birds-wire-drawing.jpg


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