Chapter: Linear Integrated Ciruits - Application of ICs

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Applications of LM 380

Amplifier requires very few external components because of the internal biasing, compensation & fixed gain.

APPLICATIONS:

 

i. Audio Power Amplifier:



·           Amplifier requires very few external components because of the internal biasing, compensation & fixed gain.

 

·           When the power amplifier is used in the non inverting configuration, the inverting terminal may be either shorted to ground, connected to ground through resistors & capacitors.

 

·           Similarly when the power amplifier is used in the inverting mode, the non inverting terminal may be either shorted to ground or returned to ground through resistor or capacitor.

 

·           Usually a capacitor is connected between the inverting terminal & ground if the input has a high internal impedance.

 

·           As a precautionary measure, an RC combination should be used at the output terminal (pin 8) to eliminate 5-to-10 MHz oscillation.

 

·           C1 is coupling capacitor which couples the output of the amplifier to the 8 ohms loud speaker which act as a load. The amplifier will amplify the Vin applied at the non-inverting terminal.

 

(ii) LM 380 as a High gain:

·The gain of LM380 is internally fixed at 50. But it can be increased by using the external components.

 

·           The increase in gain is possible due to the use of positive feedback, this setup to obtain a gain 200.

 

(iii) LM 380 as a variable Gain:

 

 

·           Instead of getting a fixed gain of 50, it is possible to obtain a variable gain up to 50 by connecting a potentiometer between the input terminals.


 

(iv) LM 380 as a Bridge Audio Power Amplifier:


·           If a certain application requires more power than what is provided by a single LM380 amplifier, then 2 LM380 chips can be used in the bridge configuration.

 

·           With this arrangement we get an output voltage swing which is twice that of a single LM380 amplifier.

 

·           As the voltage is doubled, power output will increase by four times that of a single LM380 amplifier. The pot R4 is used to balance the output offset voltages of the two chips.

 

 

(v) Intercom system using LM 380:

 

 

·           When the switch is in Talk mode position, the master speaker acts as a microphone.

 

·           When the switch is in Listen position, the remote speaker acts as a microphone.

 

·           In either phone the overall gain of the circuit is the same depends on the turns of transformer T.

 



 

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