Wireless power for mobile phones
System overview
Nov 25, 2012
V1.1
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System overview
Rx
Tx
• Embedded in mobile device
• After market case/dongle
connected through the
power connector
• Add-on connected through
dedicated WLC pins
• Embedded in
furniture/car/infrastructure
• After market mat
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Block diagram
Power
Source
Power
Resonance circuit
& power driver
TX
Coil
RX
Coil
Matching circuit
& Rectifier
Control
Unit
Control
Unit
Demodulator
Modulator
Communication
DC/DC
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Tx-Rx coils
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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.
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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-monthtransformer/ Figure 3: http://www.britannica.com/EBchecked/media/1355/Magnetic-field-B-of-two-current-loops-with-currents-in
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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
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Fig1:http://www.qitah.com/blog.htmlFig2:http://phys.org/news203691107.htmlFig3:http://patentimages.storage.googleapis.com/US20130119773A1/US20130119773A1-20130516-D00015.png
Resonance circuit and power driver
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Resonance circuit 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
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Figure 1: HIGH EFFICIENCY LOOSELY COUPLED WIRELESS POWER TRANSFER SYSTEM VIA MAGNETIC INDUCTION By ZHEN NING LOW
Resonance circuit
• The overall impedance the driver “sees” when modeled as a series RLC circuit
• At the resonance frequency the capacitive and inductive impedance equals
Amplitude
The driver then sees resistive only minimum overall impedance and the power
delivery to the Rx is maximal
Frequency
• The resonance curve changes with each different :
 Rx design (EE & ME)
 Phone material
 Misalignment from the center
 Variation during manufacturing
 Load drawn
Figure 1: http://perlgeek.de/blog-en/perl-6/rakudo-memory-leaks.html
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Driving the power
Amplitude
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
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
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Data modulation
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Data modulation
Power
driver
Modulator
Matching
circuit &
Rectifier
Demodulator
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
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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….
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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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