Is there any physical device called current source?
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The current mirror circuit is one very common current source used mostly within ICs:







simulate this circuit &ndash; Schematic created using CircuitLab

A linear regulator can be used to make a current source:







simulate this circuit

It's also possible to make a current source from an op-amp:







simulate this circuit

Most simple current source can be made of just two parts, JFET and resistor. This circuit bahave mostly like above by utilizing cutoff voltage of JFET as reference.






simulate this circuit