50 watt audio amplifier LM3876
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October - 27 - 2011
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50 watt audio amplifier.
LM3876 is a high performance audio power amplifier IC from National Semiconductors. The
LM3876 can deliver 50watts of output power into an 8 ohm loudspeaker. LM3876 has excellent
signal to noise ratio and has wide supply voltage range. Other features of LM3876 are output to
ground short circuit protection, input mute function, and output over voltage protection, etc.
Applications of LM3876 are component stereo, compact stereo, surround systems, self powered
speakers, etc.
Description.
The 50 watt audio amplifier circuit shown below is designed based on the application diagram
from the data sheet of LM3876. Some modifications are made on the original circuit for
improving the performance. The bipolar electrolytic capacitor C7 is the input DC decoupling
capacitor. R4 is the input resistance. R2 & R1 and bipolar electrolytic capacitor C5 forms a
feedback circuit. C2, C1 are filter/by-pass capacitors for the positive supply rail. C4 & C3 are the
filters/by-pass capacitors for the negative supply rail. The feedback resistor R2 sets the gain of
the amplifier. L1 provides high impedance at high frequencies so that R7 may decouple
capacitive loads. R3 is the mute resistance which allows 0.5mA to be drawn from pin8 to turn
the mute function OFF. S1 is the mute switch. Resistor R6 and capacitor C8 forms a Zobel
network which improves the high frequency stability of the amplifier and prevents oscillations.
Circuit diagram.
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