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Page 26 of 50
IRAUDAMP5 REV 3.1
I
IRAUDAMP5 can be used as output inductors evaluation tool
Results of THD+N vs. Output Power with Different Output Inductors
Fig 29
Self-Oscillating PWM Modulator
The IRAUDAMP5 Class D audio power amplifier features a self-oscillating type PWM
modulator for the lowest component count, highest performance and robust design. This topology
represents an analog version of a second-order sigma-delta modulation having a Class D
switching stage inside the loop. The benefit of the sigma-delta modulation, in comparison to the
carrier-signal based modulation, is that all the error in the audible frequency range is shifted to
the inaudible upper-frequency range by nature of its operation. Also, sigma-delta modulation
allows a designer to apply a sufficient amount of correction.
The self-oscillating frequency (Fig 30) is determined by the total delay time inside the control
loop of the system. The delay of the logic circuits, the IRS2092S gate-driver propagation delay,
the IRF6645 switching speed, the time-constant of front-end integrator (e.g.R13, R33, R31, R21,
P1, C17, C21, C23 and C1 for CH1) and variations in the supply voltages are critical factors of
the self-oscillating frequency. Under nominal conditions, the switching-frequency is around
400kHz with no audio input signal and a +/-35V supply.
0.0001
100
0.001
0.01
0.1
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10
%
100m
200m
500m
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5
10
20
50
100
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W
T
T
T
T
T
T
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T
T
Summary of Contents for IRAUDAMP5
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