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PurePath™ Smart Amp User Manual (TAS5766M/68M)
29
5.2
Power Supply Current at Audio Frequencies
An ideal power supply can deliver infinite amounts of current without a reduction in its output
voltage. In reality, a power supply maximum current output depends on its series impedance. In
practical audio applications, where the decoupling techniques are limited by cost and size, audio
frequencies are mostly driven by the supply itself and not by decoupling/bulk capacitors. The
time constants associated with audio frequencies (especially the bass and mid areas) would
require a large amount of capacitance which may be deemed impractical for most applications.
Smart Amp will help protect the speaker against thermal failure associated with high currents for
prolonged periods of time. This means that a large signal will be reduced in amplitude and settle
into a steady level corresponding to a safe output power. The plot below shows an example
6V
peak
1 kHz signal that is attenuated to a safe level. The 24V power supply in this example has
a 2-ohm series resistance and the amplifier is driving an 8-ohm load. The supply voltage drop
and current for 100uF and 1000uF bulk capacitors are shown.
Figure 10. Effects of Decoupling for Audio Frequencies
Note that for a bridge-tied-load (BTL) amplifier, the current ripple at the supply is twice the
frequency of the input signal.
-5
0
5
0
0.002
0.004
0.006
0.008
0.01
Vol
tage
(V
)
Time (s)
Input Signal
23
23.2
23.4
23.6
23.8
24
0
0.002
0.004
0.006
0.008
0.01
Vol
tage
(V
)
Time (s)
Supply Voltage
1000uF
100uF
0
0.2
0.4
0.6
0
0.002
0.004
0.006
0.008
0.01
Cur
rent
(A
)
Time (s)
Supply Current
1000uF
100uF
