High precision controllable current source

The invention discloses a high precision controllable current source which comprises a voltage-current switching circuit used for switching a reference voltage and generating a first current, a current mirror circuit used for switching the first current to a second current, and an output circuit used for switching the second current to a third current, outputting the third current and keeping the output current to be constant. The high precision controllable current source has simple structure, is easy to realize and can be applied to an LED driving circuit.