APEC 2010 Presentation
Transcript of APEC 2010 Presentation
A Low-Cost Adaptive Multi-Mode Digital Control Solution
Maximizing AC/DC Power Supply Efficiency
Feb 24, 2010
Yong Li & Jerry Zheng
iWatt Inc.Los Gatos, CA 95032
Outline
Review of existing AC/DC control solutions for energy efficiency
Proposed new low-cost high-efficiency digital control solution
• System architecture• Operational principal• Experimental results• Cost analysis
Summary
Efficiency Issues in Conventional PWM Power Supplies
Energy efficiency standards (EPA 2.0, etc.) specify the average efficiency by testing at 100%, 75%, 50%, and 25% of rated output current, and then computing the arithmetic average of these four values
At most times power supplies operate at medium to light loads
Improving light-load efficiency is the key for green power
Poor efficiency at light load
Conventional PWM/PFM Controls to Address Efficiency Issue
PFM Control
• Audible noise issue when switchingfrequency FSW drops to human audio rangebut still significant energy remains
~16kHz
PFM
IO
IO
VO
FSW
Audible Noise
PWM/PFM Control
100%
PWM
IO
IO
VO
FSW
PFM
25%
•Transition far below 25% load•No help on average efficiency
PFM Control w/ Frequency Clamp
•Voltage regulation and ripple issues at lighter load
•Suffers on no-load standby power
~20kHz
PFM
IO
IO
VO
FSW
Clamped
New Digital Green-Mode AC/DC Solution
iW1696
No feedback/regulationcomponents at secondary side
Extremely Low Cost
BJT
No RCD Clamp Needed for <3W due to BJT slow di/dt
Simple Windings No Y-Cap DesignSimple EMI filter
High Efficiency by Design
Top side
Bottom side
Example Circuit Board
SecondaryPrimary
Digital Controller iW1696
SOT-23, 5 pin
BJT
Cell-Phone Charger Application
+Vin
VSENSE
VCC
ipri
isec
iW1696 Series Controller
Ipri
isec
System Architecture• True digital peak-current mode control • Primary-side feedback eliminates opto-isolators and simplifies design• Tight 2% CV and 3% CC regulation w/ primary-side-only feedback
Built-in Multi-Layer Protections- OCP, OVP, output short - Current sense resistor short - Auto-restart current limit
High Efficiency by Design- Dynamic base current control ensures
BJT always works in optimal switching conditions - Adaptive multi-mode PWM/PFM control- Unique valley-mode switching
Multiple U.S. Patents Granted/Pending
Rsense
Adaptive Multi-Mode PWM/PFM ControlUnlike conventional approaches, digital controllers are well suited for multi-mode PWM/PFM
operation in response to varying load
As load changes from 100% to 0%, the controller goes through multiple PWM and PFM modes
U.S. Patent Pending
VO
Fsw
IO100%
b) PFM--- For medium to light load efficiency improvement
PFM
PFM
c) DPWM (Deep PWM)---i) Avoid audible noiseii) Provide smooth transition to very-light load
DPWM
DPWM~20kHz
d) DPFM (Deep PFM)---i) Energy has been reduced to insignificant level
when the switching frequency drops to audio band ii) Smoothly transition to no-load operationiii) Minimize no-load standby power consumption
DPFM
DPFM
IO
a) PWM--- For heavy load operationPWM
PWM 40kHz-65kHz
Conventional Valley Mode Switching (VMS)
Used in flyback to reduce switching loss and EMIi) After a switch has been turned off, if the switch is turned on at a Valley, the switching loss is reduced--- “quasi-resonant” or “valley mode” switching
ii) EMI can be reduced due to lower dv/dt
BJT VCE
Issues with Conventional VMS schemesi) Typically switch turns on at the First Valleyii) Work with variable switching frequency only iii) Can be challenging for EMI filter designiv) Switching frequency can be as high as 130kHz,
not suitable for BJT’s
First Valley
Unique Valley-Mode Switching
• No modification to the basic main control algorithms • Always turn on at the “local” valleys across the entire load range• Work with constant frequency PWM, variable frequency PFM, and/or their combinations• No frequency clamping or other performance compromise
Light Load Heavy Load
Seamlessly integrated with the adaptive multi-mode PWM/PFM controlin iW1696 series digital controllers
U.S. Patent Pending
Measured Operational Waveforms
PWMPFMDPWMDPFM
CC
IO
VO
Measured Switching Frequency vs. Load Changes
• No audible noise heard during the entire load range
• Lower switching frequency at high line, and higher switching frequency at low line----further reduces power losses
• Digital control enables flexible and easy configuration for different applications
PWM
PFM
DPWM
DPFM
PWM
PFM
DPWM
DPFM
Adaptive Digital Control Flattens Efficiency Curve
Meet EPA 2.0 Efficiency Spec.with lots of Margin
EPA2.0 (Final) for Low Voltage Model (Pno=2.85W) 0.075 (2.85 ) 0.561 64.0%Ln W× + =
Measured iW1696-Controlled 5V/550mA Power Supply Efficiency
Digitally-Controlled BJT SolutionsSimplify EMI Design
• BJT switching--- Inherent slower di/dt and dv/dt
• Valley-mode switching--- Further reduces dv/dt --- Spreads frequency spectrum with
natural frequency jittering
• Digital frequency white noise generation
Net Effects
(Persistence Mode)
Vsense
Ipri
CM Noise Comparison
BJT Drive MOSFET Drive
(Measured between transformer primary and secondary windings)
2.7V pk-pk 3.6V pk-pk• Dynamic base drive current control
--- Optimizes BJT switching conditions
230VAC/50Hz,Live 230VAC/50Hz,Neutral
QP
AV AV
QP
Conducted EMI
Measured EMI Performance--- No Y-Cap, No CM Choke, Simple Transformer
• Measured on typical iW1696 demo board• Individual designs may vary
230VAC/50Hz,Vertical 230VAC/50Hz, HorizontalRadiated EMI
Lowest Total System Bill-of-Material Cost
Typical 5V/550mA DesignActual Circuit
• Estimated based on typical 5V/550mA design• Individual designs may vary
Summary
• 5-pin primary-side digital controller with built-in BJT base driver• Dynamic BJT base drive current control• Adaptive multi-mode PWM/PFM control • Unique valley mode switching • No audible noise, voltage regulation or other performance compromise
iW1696 series digital control solutions offer the lowest total system BOM cost, and achieve the highest efficiency and lowest EMI for low-power (< 5W) AC/DC power supplies available in the industry.
Low-Cost Green Power by Design
World-wide energy standards are being tightened. iWatt innovative digital control platforms will enable development of new solutions that meet the emerging requirements.