4 example 4: lm1877 watts into 4w, 5 example 5: lm4861 watt into 4w, An168 – Cirrus Logic AN168 User Manual
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AN168
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AN168REV2
2.4 Example 4: LM1877-- 2 Watts into 4
Ω
The schematic for the LM1877 speaker driver is
shown in Figure 25. The LM1877, from National
Semiconductor, is capable of supplying 2 Watts of
RMS power into a 4
Ω load with less than
2% THD. The gain required to achieve 2 Watts is
+9 dB, which is implemented with an attenuation
stage of -17 dB followed by the LM1877 gain
implemented as +26 dB.
The high-pass corner frequency near 300 Hz is
given by:
The low-pass corner frequencies near 4 kHz are
given by:
2.5 Example 5: LM4861-- 1 Watt into 4
Ω
The schematic for the LM4861 speaker driver is
shown in Figure 26. Note that the power supply for
this speaker driver is +5V. The LM4861, from
National Semiconductor, is capable of supplying
1 Watt of RMS power into a 4
Ω load with less than
2% THD. The gain required to achieve 1 Watt is
+6 dB.
The high-pass corner frequency near 300 Hz is
given by:
The low-pass corner frequency near 4 kHz is given
by:
Gain
R2
R1
R2
+
--------------------
⎝
⎠
⎛
⎞
1
R3
R5
-------
R6
R5
-------
+
+
⎝
⎠
⎛
⎞
×
=
Fhp
1
2
πC1 R1 R2
+
(
)
----------------------------------------
≈
Flp
1
2
πC2 R1 R2
||
(
)
---------------------------------------
≈
Gain
2
R2
R1
-------
⎝
⎠
⎛
⎞
×
=
Fhp
1
2
π C1
(
) R1
(
)
-------------------------------
=
Flp
1
2
π C2
(
) R2
(
)
-------------------------------
=