IRAUDAMP1 revB
High Power Class D Audio Power Amplifier
using IR2011S
Features
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Complete Analog Input Class D Audio Power Amplifier
500W + 500W Peak Stereo (2CH) Output
THD+N=0.008% @1kHz, 100W, 4Ω
High Efficiency 93% @350W, 1kHz, 4Ω
Simple Self Oscillating Half-Bridge Topology
Includes all Local House-keeping Power Supplies
Protection Functions
Wide Operating Supply Voltage Range ±25 ~ 60V
Immune to Power Supply Fluctuations
Description
The IRAUDAMP1 is an example of a simple complete class D audio power amplifier design using
the IR2011S, high speed high voltage gate driver IC. The design contains protection functions
and house keeping power supplies for ease of use. This reference design is intended to
demonstrate how to use the IR2011S, implement protection circuits, and design an optimum PCB
layout.
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Resetting Protection
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Turn off ±50V at the same time
Wait until supply voltage drops to less than 5V
Apply ±50V at the same time
Apply audio signal
Power Supply
The IRAUDAMP1 requires a pair of symmetric dual power supplies ranging from ±25V to ±60V. A
regulated power supply is preferable for performance measurements, but not always necessary.
The bus capacitor, C38-41 on the board along with high frequency bypass C31, C32, C35, and
C36; are designed to take care only of the high frequency ripple current components from the
switching action. A set of bus capacitors having enough capacitance to handle the audio ripple
current must be placed outside the board if an unregulated power supply is used.
Bus Pumping
Since the IRAUDAMP1 is a half bridge configuration, the bus pumping phenomenon occurs when
the amplifier outputs low frequency signal is below 100Hz. The bus pumping phenomenon is
unavoidable; significant bus voltage fluctuations caused by a reverse energy flow coming back to
the power supply from the class D amplifier. This might cause an unacceptable instablility
condition in the feedback system of a power supply.
The bus pumping becomes worse in the following conditions.
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lower the output frequency
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lower the load impedance
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higher the output voltage
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smaller the bus capacitance in bus capacitors
If the bus voltage become too high or too low, the IRAUDAMP1 will shutdown the switching
operation, and remain in the off condition until resetting the protection using the method
described above.
One of the easiest countermeasures is to drive both of the channels out of phase so that the
reverse energy from one channel is consumed by the other, and does not return to the power
supply.
Input Audio Signal
A proper input signal is an analog signal below 20kHz, up to 5Vrms, having a source impedance
of less than 600
Ω.
A 30-60KHz input signal can cause LC resonance in the output LPF,
resulting in an abnormally large amount of reactive current flowing through the switching stage.
The IRAUDAMP1 has a C-R network to dump the resonant energy and protect the board in such
a condition. However, these sub-sonic input frequencies should be avoided.
Load Impedance
The IRAUDAMP1 is designed for a load impedance of 4Ω and larger. The frequency response
will have a small peak at the corner frequency of the output LC LPF if the loading impedance is
higher than 4Ω. The IRAUDAMP1 is stable with capacitive loading, however, it should be realized
that the frequency response will be degraded by a heavy capacitive loading of more than 0.1µF.
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