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Kalyan Siddabattula
System Architect
bqTESLA Wireless Power Solutions
TEXAS INSTRUMENTS
1
Why Not A Wire? The case for wireless power
http://dailyreporter.com/files/2009/07/powertheft-070709.jpg
Wireless Power – Replaces A Wire
• Wireless Power is a convenient method of transferring energy from one
physical device to a second physical device without contacts
• This allows devices to be powered or batteries to be charged
• It is mostly a convenience issue for consumers and offers
• Different methods or wireless power transfer are available based upon
power level requirement and use case
– Inductive resonant charging
– Capacitive
– Solar/Light
– Vibratory
– Audio 2
Wireless Energy Transfer – Overview
Wireless Energy
Transfer
Electromagnetic
Induction
Electromagnetic
Radiation
Electrodynamic
Induction
Electrostatic
Induction
Microwave/ RF
Power
Light/ Laser
Power
Inductive coupling Magnetic Resonant
Induction
Near Field Far Field
Magnetic field Electric field
Why Do Wireless Charging
• Convenience
• Convenience
• Convenience
• Connector fatigue and failure can be avoided
• Hermetically sealed devices are possible
• Ability to “graze” energy rather than “gorge” means users will have well
charged devices when they pick up a device and go
But It’s Not As Efficient As A Wire?!
• Isn’t a wire inherently more efficient than wireless?
• Isn’t a wire 100% efficient?
• What’s the maximum efficiency of wireless power transfer
anyway?
http://gomadic.us/imgs-prod/charger/sony-bloggie-touch-rapid-wall-ac-charger.jpg
• Power transmitted through shared magnetic field
– Transmit coil creates magnetic field
– Receive coil in proximity converts field into voltage
– Shielding material on each side directs field
• Power transferred only when needed
– Transmitter waits until its field has been perturbed
– Transmitter sends seek energy and waits for a digital response
– If response is valid, power transfer begins
• Power transferred only at level needed
– Receiver constantly monitors power received and delivered
– Transmitter adjusts power sent based on receiver feedback
– If feedback is lost, power transfer stops
I
z < D
D
AC to DC Voltage
Conditioning
Communication
and Control
Rectification Drivers Li Ion
Battery
Controller V/I
Sense
Power
Transmitter Receiver
Communication
Wireless Power System Overview
Current Wired charger
Typically
Flyback
Losses
Transformer
Electronics
Diode
Rectification
Regulation
Losses
Rectifier
Regulation
110VAC/
240VAC
DC
voltage
From wall
Primary
80%-90% Efficiency
Secondary
80% - 90% Efficiency
Filter/Rectifier
95% Efficiency
Total System efficiency is ~ 50% to 64% TO BATTERY
When efficiency of wire (~95%) is included, System efficiency can be ~72% TO CHARGER or even less
than 47% TO BATTERY
Diode
Bridge
HF AC
Charger
5V
1.0A
Battery
85% Eff
4.35V
1.0A
Total System efficiency is ~ 60% to 76% TO CHARGER
Current TI Wireless Power EVM System
AC-DC
60%-80%
Efficiency1
110VAC/
240VAC
1. Assuming 80% Adapter efficiency
2. All numbers are typical of a nominal interface gap of 3.7mm, optimal position
3. Peak efficiency shown is shown at 3.5W output power
Receiver
89% Efficiency
19VDC 5V
1.0A
Peak Electronics
Efficiency 93%
HF AC
Transmitter
95% Efficiency
Coil to Coil
89% Efficiency
LV Half Bridge
to energize Coil
Synchronous FB
Regulator
Charger
DC System efficiency 75% TO CHARGER
Total System efficiency is 60%1 TO CHARGER
bqTesla System Efficiency Breakdown
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Eff
icie
ncy (
%)
Output Power (W)
Tx Eff. Magnetics Eff. Rx Eff. System Efficiency
System Eff
TX Eff
Magnetics Eff
RX Eff
Measured from DC input of Transmitter to DC output of Receiver
- Wireless power in series with existing system
- Adapter sense turns off wireless power when adapter is present
- Termination disables wireless power once charge is complete
RX Architecture – Main Board Power Supply
RX Architecture – Main Board Charger
• Wired and wireless charger in parallel
• Adapter sense turns off wireless charger when adapter is present
• Highest efficiency solution when observing power transferred to the battery
Direct Charging vs. Discrete Charging
Transmitter Receiver
Charger
System/ Battery
Discrete Charging Solution
Transmitter Receiver
Charger
System/ Battery
Direct Charging Solution
Direct charging allows the RX to become the battery charger allowing for
elimination of a power stage. This allows highest efficiency path and maximal
use of thermal budget
Efficiency Data Comparison-Direct vs. Discrete Charging Topologies
Over 10% improvement
by going to direct charge
Direct charge solution allow you to turn off the “wired” charger and thus allow you
to allocate the thermal budget of the “wired” charger to the “wireless” charger.
RX Architecture – Output Voltage
• Output Voltage can have a great impact on the efficiency
• Coil and synchronous rectifier I2R losses are current based
50.00%
55.00%
60.00%
65.00%
70.00%
75.00%
80.00%
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Efficiency And Output Voltage
7V Vo Efficiency
5V Vo Efficiency
WP
Transformer
Voltage Regulation Architecture
TX
RX
Sync
Rect
DC
Adapter
Buck
Reg
Flyback
One FET H-Bridge
Four FETS
H-Bridge
Four FETS
Two FETS
Inductor Transformer
Buck
Charger
Two FETS
Inductor
TX
RX
Sync
Rect
DC
Adapter
Dynamic
LDO
Reg
Flyback
One FET H-Bridge
Four FETS
H-Bridge
Four FETS
One FET
NO Inductor Transformer
Buck
Charger
Two FETS
Inductor
WP
Transformer
Acts like a Buck
Architecture Comparison
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Buck Architecture
TI -- Dynamic LDO
Architecture Comparison
Next Gen TI Wireless Power EVM System
Charger
AC-DC
60%-80%
Efficiency1
110VAC/
240VAC
1. Assuming 80% Adapter efficiency
2. All numbers are typical of a nominal interface gap of 3.7mm, optimal position
3. Peak efficiency shown is shown at 3.5W output power
Receiver
95% Efficiency
19VDC
DC System efficiency 80% TO CHARGER
Peak Electronics
Efficiency 96%
Total System efficiency is 65%1 TO CHARGER
HF AC
Transmitter
95% Efficiency
Coil to Coil
89% Efficiency
LV Half Bridge
to energize Coil
Synchronous FB
Regulator
What Architecture Works Best?
Battery
110VAC/
240VAC
1. All numbers are typical of a nominal interface gap of 3.7mm, optimal position
2. Peak efficiency shown is shown at 3.5W output power
Receiver
93% Efficiency
DC 4.35V
1.0A
Peak System efficiency 75% TO BATTERY
Total System efficiency is > 70% TO BATTERY
HF AC
Transmitter
88% Efficiency
Coil to Coil
89% Efficiency
Diode
Bridge
Rectifier
95% Efficiency
HV Half Bridge
to energize Coil
Synchronous FB
Charger
Direct AC TX1 Direct Charge RX
Potential Wireless Charging Implementations Compared
Wall Adapter Transmitter Receiver Expect Eff .
AC to Battery
Comments
Current
Wired Charger
N/A N/A ~ 50 - 65% As low as 47% when
cable eff is included
19V DC Out Single Coil
No Magnet 7V into Charger 52 % Best available
Wireless Solution
Today
5V DC Out Single Coil
No Magnet
7V into Charger 45 % 5V Adapter Design
important
19V DC Out Single Coil
No Magnet
Next Gen Direct charge 62% Direct charge
offers higher
efficiency
None Direct AC TX Next Gen Direct charge 65 - 70% As good as wired?
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