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I've been looking at the schematics of the LM386 amplifier, but there is a symbol I don't recognise, it looks like a circle with an arrow in it (but it's not a voltage generator of course), can someone tell me what it means, please?

1 The whole schematic: 2

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  • \$\begingroup\$ Yes, I know the common symbol, it just looked different on this one, because the arrow isn't "floating" inside the circle, like it is commoly depicted, I just thought maybe it means something else, but I guess not, then. \$\endgroup\$
    – Gergely Fazekas
    Sep 19, 2021 at 7:42
  • \$\begingroup\$ Sometimes it is 2 circles, sometimes arrow is on outside and I guess sometimes connected. \$\endgroup\$
    – StainlessSteelRat
    Sep 19, 2021 at 20:33

2 Answers 2

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That is a current source. It will be a sub-circuit to generate a reasonably constant current through the push-pull output transistor biasing circuit.

To avoid cross-over distortion (a discontinuity on the changeover from sourcing current through the upper transistor to sinking current through the lower transistor) on the output the diodes are added to compensate for the voltage drop across each base-emitter junction. Running a constant current through these keeps the voltage drop across them reasonably constant.

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Based on the context this is a current source. Not the most standard symbol for it - most commonly that would be represented by two overlapping circles or an arrow "floating" inside of a circle.
Current Source Symbol (US?)

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    \$\begingroup\$ For what it's worth, the arrow-in-a-circle symbol is commonly used for an ideal current source in the U.S.A. I think the overlapping-circles symbol might be a DIN convention. \$\endgroup\$
    – Elliot Alderson
    Sep 18, 2021 at 16:29
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    \$\begingroup\$ @ElliotAlderson: I think you are correct. The standards are rather "free" around the world. The arrow "floating" inside of a circle connected at the perimeter is common. Not exactly the rendering in the schematic. \$\endgroup\$
    – Martin Vana
    Sep 18, 2021 at 16:44
  • \$\begingroup\$ Yes, I've seen the "floating" arrow in a circle before, but on this schematic it didn't look quite like that, but I guess then it means the same. \$\endgroup\$
    – Gergely Fazekas
    Sep 19, 2021 at 7:38
  • \$\begingroup\$ This symbol looks more like a galvanometer \$\endgroup\$
    – Always Confused
    Nov 4, 2022 at 20:50

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