Author Topic: Audio Amplifier Application Schematic  (Read 1164 times)

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Offline eerocketmanTopic starter

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Audio Amplifier Application Schematic
« on: April 15, 2019, 01:23:38 am »
Hi Everyone,

I am making a bluetooth speaker using the the LM2976 (http://www.ti.com/lit/ds/symlink/lm2876.pdf). the typical aplication schematic is pretty straight forward except for a BJT connected to the power leads of the IC. Could someone explain what the purpose of the BJT is? I have highlighted the component in question on the attached image.

Thanks!!
 

Offline Circlotron

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Re: Audio Amplifier Application Schematic
« Reply #1 on: April 15, 2019, 01:27:35 am »
With split pos and neg supply rails pin 7 is normally grounded i.e. halfway between pos and neg. With a single supply rail setup like in this diagram the BJT supplies pin 7 with approx half rail voltage.
 
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Offline eerocketmanTopic starter

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Re: Audio Amplifier Application Schematic
« Reply #2 on: April 15, 2019, 01:32:30 am »
Got it, thank you!
 

Offline coromonadalix

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Re: Audio Amplifier Application Schematic
« Reply #3 on: April 15, 2019, 01:32:53 am »
the 2n3904  is not an bjt,  its an npn transistor
 

Offline eerocketmanTopic starter

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Re: Audio Amplifier Application Schematic
« Reply #4 on: April 15, 2019, 01:35:30 am »
Could you elaborate on the difference? I  thought NPN transistors were BJTs.
 

Offline coromonadalix

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Re: Audio Amplifier Application Schematic
« Reply #5 on: April 15, 2019, 02:46:12 am »
sorry    its bipolar junction transistor indeed   my bad  :palm:    mixed with an ujt  loll
 

Offline Audioguru

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Re: Audio Amplifier Application Schematic
« Reply #6 on: April 15, 2019, 03:27:26 pm »
What speaker impedance and power supply voltage are you using for the LM2876 amplifier IC?
 


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