Electronic – Simple LM386 Circuit RC Branch Question


Please take a moment to checkout at the LM386 circuit below. The circuit comes directly from the LM386 specifications document:

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My question revolves around the output branch consisting of the 0.05 microfarad capacitor and the 10 ohms resistor.

At first I thought that this branch acted as some kind of RC filter but then I realized that on all RC filters (as far as I know) filtering is achieved by taping into the node between the capacitor and the resistor (which is not the case on this branch).

So what is this branch supposed to do? Is it for filtering? Also, what effect does the branch consisting of the 250 microfarad and the speaker has on the output signal? It looks like at the end both branches will combine in parallel and I am having trouble understanding how all these component work together.


Best Answer

It's called a Zobel Network. The purpose is to neutralize the effect of the inductance of the speaker.

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The 250uF simply blocks DC from the output bias point of the amplifier output stage, which normally sits around half the supply voltage with no output, and swings from close to GND to close to the positive rail when it is providing full output.

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