Having solved the mystery of ["pulling" and "pushing" devices](https://electronics.stackexchange.com/q/664001/61398), it would be interesting to do the same with "sourcing" and "sinking" devices.

Background
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A transistor with a constant base-emitter voltage represents a *constant current source* (to be more precise, we should also include the power source).

For example, in the CircuitLab schematics below, I have adjusted the base-emitter voltage so that to pass 1 mA current through the load. If you want to change it, open Vin's *parameters* window, hover the mouse over RL, and adjust Vin while looking at the reading. If the *parameters* window covers RL, then move the schematic to the right edge of the screen, open and click on *parameters* to pin it, and return the schematic to the left side of the screen.

Note something interesting in this arrangement - the collector and emitter currents are equal because the base current is not added to the emitter one.

Varieties
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Depending on the place of insertion, we call this device by different names.

"Current source"
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If we connect the transistor Q with its emitter to the positive supply rail, and the load RL to ground, we call it "current source".

<!-- Begin schematic: In order to preserve an editable schematic, please
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![schematic](https://i.sstatic.net/TqSzW.png)

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"Current sink"
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If we connect an NPN transistor Q with its emitter to ground, and the load RL to Vcc, we call it "current sink".

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![schematic](https://i.sstatic.net/ZFqWR.png)

<!-- End schematic -->

Both?
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But what should we call (what is) the transistor when it is "floating" between two loads RL1 and RL2?

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![schematic](https://i.sstatic.net/JMCnp.png)

<!-- End schematic -->