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clases de amplificadores : A

1. COMMERCIALIZING CLASS D
AMPLIFIER TECHNOLOGIES
Paul Mathews & Rick Jeffs
Rane Corporation
Mukilteo, WA 98275 USA
[email protected], [email protected]

2. Commercializing Class D Amplifier Technologies 2
Smaller, lighter power amplifiers
•Commercial Marketplace Trends
–Multichannel sound
–More audio zones
–Redundancy for safety systems
–Reduced power consumption
•Product response: switchmode power supplies and
amplifiers in small packages
Don’t expect to compete
with highly-evolved linear
technologies on cost alone.

3. Commercializing Class D Amplifier Technologies 3
Product Requirements
•Mains power
–Universal mains
–High power factor, low inrush
–Low EMI radiation and susceptibility
•Inputs pro audio +4 to +22 dBu
•Outputs
–100 watts adequate for many multi-channel applications
–Audio signals: design for crest factor ~12 dB, i.e., avoid overly-
conservative power and thermal design
–Design for load faults and non-constant load impedances
•Cost
–Cost/watt similar to older products: no adder for new features

4. Commercializing Class D Amplifier Technologies 4
Product Requirements (cont’d)
•Reliability and redundancy
–Commercial users demand reliability
–Safety applications require redundancy
•Enclosure
–Smaller is better, 1U
•Certifications
–UL, CE mark, FCC
–Primary challenges: radiated EMI, safety

5. Commercializing Class D Amplifier Technologies 5
System Design Considerations
•Power requirements vary greatly due to:
–Signal dynamics
–Complex load impedance
–Amplifier and Supply efficiencies
•These variables impact:
–Amplifier size and cost
–Thermal management requirements
–ac mains current draw and EMI

6. Commercializing Class D Amplifier Technologies 6
Amplifier Technologies
•Switchmode amplifiers have size and weight advantage
•Monolithic switchmode technologies
–Advantages: cost, size, EMI
–Disadvantages: IC process and packaging voltage, current, thermal
limits
•Digital-in/digital-out disadvantage: little or no benefit of
feedback
•Our technology selection:
–fully-integrated, analog-in/PWM out, silicon-on-insulator IC
–Full-bridge outputs to maximize power output within voltage limits
–High fixed PWM clock (307 kHz) for simplified output filtering

7. Commercializing Class D Amplifier Technologies 7
Inherent Limitations
•All amplifier technologies have limitations:
–Voltage, Current and Thermal Dissipation
–Exceeding any limit can cause unacceptable signal distortion or
disruption
•Challenge of designing within voltage/current limits:
–Must know:
•Signal dynamics, load impedance, temperature
–These are non-stationary parameters
•For component amplifiers: load impedance is almost totally unknown
in advance

8. Commercializing Class D Amplifier Technologies 8
Over Design?
•One solution is to over-design the system
•Over designing adds cost:
–Power Amplifier selection
–Size and weight
–Thermal management
–ac mains requirements

9. Commercializing Class D Amplifier Technologies 9
Highly-Integrated Solution
•Integrating:
–Supervisory control of all functions
–Load and temperature aware dynamics control
–Efficient power supply with PFC
–Efficient class d amplifiers
•Allows:
–Small size and moderate power
–Optimum performance into a given load
–Reliable audio signal integrity
–Easy system design and setup
–New features

10. Commercializing Class D Amplifier Technologies 10
Integrated Power Amplifier

11. Commercializing Class D Amplifier Technologies 11
PFC
FAULT FLAG
MASTER/SLAV E
COMBI NATI ON CONTROLER
SMPS
2-SW FORWARD
FUSE
EMI FI LTER
I NRUSH
OVER VOLTAGE
H
3
G
2
N
1
I EC
APPLI ANCE
I NLET
(100 kHz )
(200 kHz )
GND
+25
-25
SENSI TI VI TY
HI GH-PASS
20-40-60-80
COMPRESSOR
PEAK LI MI TEREXPAND
FI LTER
ATT.
F
I
L
T
E
R
+25
-25
CLK
3 dB
6 dB
12 dB
24 dB
LI MI T
COMP
FAULT
LOAD
EXP READY
DSP
HOST
SENSI TI VI TY
GND+5A
REMOTE LEVEL
CURRENT SENSE
TEMP SENSE
+
-
AMPLI FI ER
BACKUP
LOAD
+4+22
1
COMP OFF/10 Db
EXP ON/ OFF
00
01
01
11
20 Hz
40 HZ
60 Hz
80 Hz
MODE:
STANDBY
MUTE
ON
MODE
SUPPLY SENSE
300 kHzI NPUT LI MI T
r ms
LEVEL
RMS
LOW VOLTAGE
FLYBACK
Vr elay
+5d
+3.3
+5a
+
GNDVR 1
+
-
SUPPLY CLOCK
SU PPLY CLOCK
AMP CLOCK
SUPPLY CLOCK
REMOTE
LEVELADC
AV G LOAD Z
TEM P PW R
CLASS-D
AMPLIFIER
FILTER
ATT.
F
I
L
T
E
R
+25
-25
CLK +
-
BACKUP
LOAD
MODE
300 kHz
+
GNDVR1
+
-
CLASS-D
AMPLIFIER
SENSITIVITY
HIGH-PASS
20-40-60-80
COMPRESSOR
PEAK LIMITEREXPAND
DSP
INPUT LIMIT
rms
LEVEL
RMS
REMOTE
LEVEL
TEMP PWR
AVG LOAD Z
FAULT FLAG
MASTER/SLAVE
3 dB
6 dB
12 dB
24 dB
LIMIT
COMP
FAULT
LOAD
EXP READY
HOST
SENSITIVITY
GND+5A
REMOTE LEVEL
CURRENT SENSE
TEMP SENSE
AMPLIFIER+4+22
1
COMP OFF/10 Db
EXP ON/OFF
00
01
01
11
20 Hz
40 HZ
60 Hz
80 Hz
MODE:
STANDBY
MUTE
ON
SUPPLY SENSE
SUPPLY CLOCK
AMP CLOCK
SUPPLY CLOCK
AVG LOAD Z
PFC
COMBINATION CONTROLER
SMPS
2-SW FORWARD
FUSE
EMI FILTER
INRUSH
OVER VOLTAGE
H
3
G
2
N
1
IEC
APPLIANCE
INLET
(100 kHz)
(200 kHz)
GND
+25
-25
LOW VOLTAGE
FLYBACK
Vrelay
+5d
+3.3
+5a
SUPPLY CLOCK
Highly-Integrated Solution

12. Commercializing Class D Amplifier Technologies 12
Supervisory Host
•Operates from auxiliary supply, controls higher power
circuits
•Control all clocks to high power circuits, monitoring:
–Mains and internal supply rail voltages and currents
–Load impedance, Amplifier OK status, over-temperature
•Works with DSP to set Limiter Threshold, Fault status,
and load impedance equalization parameters
•Amplifier temperature is feedback for
–Compressor Threshold
–Fan Speed / Fault status

13. Commercializing Class D Amplifier Technologies 13
Power Supply Technologies
•Switchmode for size and weight reductions
•Power Factor Correction benefits:
–Reduced EMI
–Improved mains circuit utilization
–Reduced regulation burden for dcdc conversion

14. Commercializing Class D Amplifier Technologies 14
Power Supply PFC
•Power Factor Correction
reduces:
–peak current, rms current
–ac mains harmonics
–dcdc stage peak currents
–bulk capacitance
•Interleaving with dcdc
converter reduces EMI

15. Commercializing Class D Amplifier Technologies 15
Inrush Reduction with PFC
•PFC high V (385 V)
–high ripple tolerance
–Allows small bulk C
–Ripple removed by
post-PFC regulation
•Small capacitor
reduces charging
energy
–Faster RC time
constant for given
peak current limit
Top: PFC front end, 220 F @ 340V
Bottom: Transformer/rectifier, 10000 F @ 60V

16. Commercializing Class D Amplifier Technologies 16
Switchmode Magnetics
•Requirements:
–Low profile, low loss at high frequency
–Thermal performance consistent with audio signals, low air flow
•Technologies
–Sendust distributed-gap toroidal cores for inductors (carrying
significant ‘dc’ current)
–Single-layer and progressive windings to minimize capacitances
–Ferrite core dcdc converter transformer, Litz windings, inter-
winding shield
–Toroidal ferrite common mode transformers on mains input and
dc output

17. Commercializing Class D Amplifier Technologies 17
Switchmode Magnetics (cont’d)

18. Commercializing Class D Amplifier Technologies 18
Power Supply Attributes
•Very high incremental efficiency
–Quiescent power largely set by switching losses
•Maximal use of mains circuits
–Many more 100 watt channels per breaker
•High tolerance for brownouts and dropouts
•Internal and external fault self-diagnosis and soft
shutdown

19. Commercializing Class D Amplifier Technologies 19
Power Amplifiers
•Efficient, class d design:
–Low power loss/thermal handling requirements
–Enables voltage limiting without efficiency loss
•Silicon-on-insulator process
–Zero dead-time
–300 kHz switching rate
–Self test, self-protection: supply imbalance, over-
temperature, over-current
–External clock and remote start/stop

20. Commercializing Class D Amplifier Technologies 20
Power Amplifiers (cont’d)
•Less than ideal properties
–Very fast output overcurrent protection
•Shuts off output MOSFETs  undesirable sound
effects
–Voltage clipping (as with all amplifiers)
–Finite thermal capabilities
–Consumer audio input and gain levels

21. Commercializing Class D Amplifier Technologies 21
Power Amplifiers (cont’d)
•Integration solution:
–Control power amplifier drive signals for
trouble-free operation
–This approach also allows sensible control of
gain structure
•Basis of control: Load Impedance
Estimation

22. Commercializing Class D Amplifier Technologies 22
SENSITIVITY
HIGH-PASS
20-40-60-80
COMPRESSOR
PEAK LIMITEREXPAND
DSP
INPUT LIMIT
rms
LEVEL
RMS
REMOTE
LEVEL
TEMP PWR
AVG LOAD Z
Signal Processing

23. Commercializing Class D Amplifier Technologies 23
Load Estimation
•Maintain load voltage and supply current
statistics to estimate Z
•Average impedance for actual signals
–Not impedance at a particular frequency
•Used to set Limiter Threshold
•Margins for departures from estimated Z
•Bonus feature: load status to user

24. Commercializing Class D Amplifier Technologies 24
DSP Functions
•Limiter
–Prevents voltage and current
clipping
–Set automatically for:
•sensitivity setting
•Average load impedance
COMPRESSOR
PEAK LIMITERRMS
TEMP PWR
AVG LOAD Z
•Compressor
–Limits long-term average power
–Limits amplifier heating
–Tied to Limit Threshold

25. Commercializing Class D Amplifier Technologies 25
DSP Limiter / Compressor
•Allowable load currents
(allowing 3 dB margin) :
–8.0  load I
peak
: voltage limit,
~ 40 V swing
–4.0  I
peak
limit = 7.7 A
–1.3  I
peak
limit = 7.3 A
•Compressor characteristics:
–Tied to limiter threshold
–Long time constant
–4 dB max compression

26. Commercializing Class D Amplifier Technologies 26
DSP Functions
•High-pass filter
–Adjusted for speaker or distribution transformer
•Sensitivity
–Set gain: maximum output at maximum input
•Expander
–Reduce source noise with no signal
SENSITIVITY
HIGH-PASS
20-40-60-80
EXPAND
INPUT LIMIT
REMOTE
LEVEL

27. Commercializing Class D Amplifier Technologies 27
Metering
•Load sensitive peak
headroom
•Limit/Compress/Expand
indicators
•Fault status
•Load status
•Off/Standby/Ready
indicator
3 dB
6 dB
12 dB
24 dB
LIMIT
COMP
FAULT
LOAD
EXP READY

28. Commercializing Class D Amplifier Technologies 28
Fault Reporting and Redundancy
•Three basic features:
–Internal fault reporting
–External fault reporting
–Load switching
•Enable:
–Fault reporting to a
control system
–Automatic redundancy
switching
FILTER
ATT.
F
I
L
T
E
R
+25
-25
CLK +
-
BACKUP
LOAD
MODE
300 kHz
+
GNDVR1
+
-
CLASS-D
AMPLIFIER

29. Commercializing Class D Amplifier Technologies 29
Integration Benefits
•Predictable and low power consumption
•Reduced thermal stress
•Improved reliability
•Improved signal integrity
–no voltage or current clipping
–no thermal cycling
–no blown fuses
•New features

30. Commercializing Class D Amplifier Technologies 30
Mechanical/Thermal/EMI Design
•Integrated design is essential. Examples:
–1U form best with low mass (heatsinks, chassis, etc)
–Switchmode heatsinks can radiate or, preferably, act as
shields
–Airflow vents can compromise shielding
–Customers dislike airflow noises
•Supervisory control monitors temperature,
controls fan speed, power dissipation

31. Commercializing Class D Amplifier Technologies 31
Squeezing It In
•Small chassis makes shielding difficult
–EMI generating components close together, close to chassis 
must minimize parasitics
–Floor planning and careful placement and orientation of every
power component is essential
•Minimize capacitance of high dv/dt structures
•Minimize area of high di/dt loops and arrange for
cancellation or perpendicularity where possible
•Minimize di/dt and dv/dt by circuit design where possible
•Recognize that most power components have high dv/dt
and low dv/dt ‘sides’

32. Commercializing Class D Amplifier Technologies 32
Magnetic Loops Example
Similar analyses for dv/dt and parasitic capacitances

33. Commercializing Class D Amplifier Technologies 33
Thermal Management

34. Commercializing Class D Amplifier Technologies 34
Conclusion
•Market demands: smaller, lighter, more
channels and features with no added cost
•Our response:
–All switchmode 4-channel amplifier 4 x 100 W
–Integrated power management, audio signal
control, reliability enhancement, and other
ease-of-use features

35. Commercializing Class D Amplifier Technologies 35
Thanks for your attention
Anyone with biographical knowledge of
Danish physicist Soren Larsen (1871-1957),
said to be among the first to analyze the
‘Larsen Effect’ also known as ‘feedback
howl’, please contact me.