Wednesday 10 April 2019

Audio Amplifier op amp without feedback?


i have a question about this circuit


enter image description here


the inverting input is connected to ground , so any voltage different than 0 in the non inverting input will saturate the op amp ( correct me if i'm wrong). how can this circuit work without feedback ?



Answer




The LM386 has feedback and it sits inside the chip.


As opamp's generally do not have overall feedback (local feedback can be present though), the LM386 clearly is not an opamp, it's an audio power amplifier.


Open the datasheet and on the first page you see the internal schematic:


enter image description here


These's a 15 kohm resistor which is part of the feedback circuit together with the 150 ohms and 1.35 kohm resistors.


Never assume an IC's function from its symbol, all amplifiers (can) use a triangle shaped symbol, it is not reserved for opamps. Instead, read the datasheet so you know what it is (instead of guessing/assuming).


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