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.
LM3876 50watt audio amplifier
Notes.
- The LM3876 can be operated from a supply voltage range of /-12V to /-49V DC.
- I recommend /-35V DC for powering the IC.
- LM3876 requires a proper heat sink.
- Quiescent current of LM3876 is around 70mA
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