classdtutorial606.pdf

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Designing Practical High Performance
Class D Audio Amplifier
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Contents
Chapter 1
Chapter 2
•
•
Class D Amplifier Introduction
Theory of class D operation, Points of design
The latest Digital Audio MOSFET,
DirectFET
®
MOSFET
Importance of layout and packaging
Optimized MOSFET for no-heat sinking
Chapter 3
•
Designing Dead-time and Overload
Protection with Digital Audio Gate
Driver IC
Designing with built-in dead-time generation
How to design OCP. Tj estimation.
Chapter 4
•
Design Example
No-heat sink 100W x 6ch compact Class D amplifier
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Chapter 1 Class D Audio Overview
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Review: Traditional Class AB Amplifier
• Class AB amplifier uses
linear regulating transistors
to modulate output voltage.
＋Vcc
Feed back
＋
－
Error amp
Bias
＋
• A loss in the regulating
transistor in Class AB
amplifier is proportional to
the product of the voltage
across the device and the
current flowing through it.
－Vcc
η
= 30% at temp rise test condition.
P
C
=
V
CE
⋅
I
C
Independent of device
parameter
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Class D Amplifier
Feed back
Triangle
+VCC
Nch
Level Shift
＋
－
Error Amp
＋
COMP
Dead Time
Nch
-VCC
•Class D amplifier employs MOSFETs which are either
ON or OFF state. Therefore ideally 100% efficiency can
be achieved.
•PWM technique is used to express analog audio signals
with ON or OFF states in output devices.
•A loss in the switching device caused by 1)finite
transition speed, 2)ON state resistance and 3)gate
charge.
P
=
Psw
+
Pcond
+
Pgd
TOTAL
dependent of device parameter
can be improved further!
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