Why Not A Wire? The case for wireless power Kalyan Siddabattula System Architect bqtesla Wireless Power Solutions TEXAS INSTRUMENTS http://dailyreporter.com/files/2009/07/powertheft-070709.jpg 1
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 Near Field Far Field Electromagnetic Induction Electromagnetic Radiation Magnetic field Electric field Electrodynamic Induction Electrostatic Induction Microwave/ RF Power Light/ Laser Power Inductive coupling Magnetic Resonant Induction
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
Wireless Power System Overview Power AC to DC Drivers Rectification Voltage Conditioning Li Ion Battery Communication Controller V/I Sense Communication and Control Transmitter Receiver 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 D z < D
Current Wired charger 110VAC/ 240VAC From wall Diode Bridge Filter/Rectifier 95% Efficiency DC voltage Typically Flyback Losses Transformer Electronics HF AC Diode Rectification Regulation Losses Rectifier Regulation 5V 1.0A Charger 85% Eff 4.35V 1.0A Primary Secondary 80%-90% Efficiency 80% - 90% Efficiency Battery Total System efficiency is ~ 60% to 76% TO CHARGER 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
Current TI Wireless Power EVM System Peak Electronics Efficiency 93% 110VAC/ 240VAC 19VDC HF AC 5V 1.0A Charger AC-DC 60%-80% Efficiency 1 LV Half Bridge to energize Coil Synchronous FB Regulator Transmitter Coil to Coil 95% Efficiency 89% Efficiency Receiver 89% Efficiency DC System efficiency 75% TO CHARGER Total System efficiency is 60% 1 TO CHARGER 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
Efficiency (%) bqtesla System Efficiency Breakdown Measured from DC input of Transmitter to DC output of Receiver Tx Eff. Magnetics Eff. Rx Eff. System Efficiency 100% 90% Magnetics Eff RX Eff TX Eff 80% 70% System Eff 60% 50% 40% 30% 20% 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Output Power (W)
RX Architecture Main Board Power Supply - 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 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 Discrete Charging Solution Direct Charging Solution Transmitter Receiver Transmitter Receiver Charger Charger System/ Battery System/ Battery 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 I 2 R losses are current based 80.00% Efficiency And Output Voltage 75.00% 70.00% 65.00% 60.00% 55.00% 7V Vo Efficiency 5V Vo Efficiency 50.00% 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Voltage Regulation Architecture DC Adapter TX WP Transformer RX Sync Rect Buck Reg Buck Charger Flyback One FET Transformer H-Bridge Four FETS H-Bridge Four FETS Two FETS Inductor Two FETS Inductor DC Adapter TX WP Transformer RX Sync Rect Dynamic LDO Reg Buck Charger Flyback One FET Transformer H-Bridge Four FETS Acts like a Buck H-Bridge Four FETS One FET NO Inductor Two FETS Inductor
Architecture Comparison 80.00% Architecture Comparison 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Buck Architecture TI -- Dynamic LDO 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Next Gen TI Wireless Power EVM System Peak Electronics Efficiency 96% 110VAC/ 240VAC 19VDC HF AC Charger AC-DC 60%-80% Efficiency 1 LV Half Bridge to energize Coil Synchronous FB Regulator Transmitter Coil to Coil 95% Efficiency 89% Efficiency Receiver 95% Efficiency DC System efficiency 80% TO CHARGER Total System efficiency is 65% 1 TO CHARGER 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
What Architecture Works Best? Direct AC TX 1 Direct Charge RX 110VAC/ 240VAC Diode Bridge DC 4.35V 1.0A HV Half Bridge Rectifier to energize Coil 95% Efficiency HF AC Synchronous FB Charger Battery Transmitter Coil to Coil 88% Efficiency 89% Efficiency Receiver 93% Efficiency Peak System efficiency 75% TO BATTERY Total System efficiency is > 70% TO BATTERY 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
Potential Wireless Charging Implementations Compared Wall Adapter Transmitter Receiver Expect Eff. AC to Battery Comments Current Wired Charger 19V DC Out 5V DC Out 19V DC Out N/A N/A ~ 50-65% As low as 47% when cable eff is included Single Coil No Magnet Single Coil No Magnet Single Coil No Magnet 7V into Charger 52 % Best available Wireless Solution Today 7V into Charger 45 % 5V Adapter Design important Next Gen Direct charge 62% Direct charge offers higher efficiency None Direct AC TX Next Gen Direct charge 65-70% As good as wired?