Cirrus-logic AN168 Uživatelský manuál stáhnout pdf (Strana 34)

AN168

34 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

R1 R2+

--------------------

⎝⎠

⎛⎞

-------

⎝⎠

⎛⎞

×=

Fhp

2πC1 R1 R2+()

----------------------------------------

≈

2πC2 R1 R2

()

---------------------------------------

≈

Gain 2

-------

⎝⎠

⎛⎞

×=

Fhp

2π C1()R1()

-------------------------------

Flp

2π C2()R2()

-------------------------------

1 2 ... 29 30 31 32 33 34 35 36

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