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?