Application of precision constant current source circuit

The constant current source is a current source whose output current is kept constant, and the ideal constant current source should have the following characteristics: a) it does not change due to load (output voltage) change; b) does not change due to changes in ambient temperature; c) internal resistance It is infinite (so that its current can flow out to the outside). A circuit capable of providing a constant current is a constant current source circuit, which is also called a current mirror circuit.
The constant current source circuit is the basis for providing a stable current to ensure the stable operation of other circuits. That is, the constant current source circuit is required to output a constant current, so the device as the output stage should have a volt-ampere characteristic with a saturated output current. This can be done with a BJT or MOSFET that operates in the output current saturation state. In order to ensure the stability of the output transistor, two conditions must be met: a) its input voltage should be stable - the input stage needs to be a constant voltage source; b) the output resistance of the output transistor is as large as possible (preferably infinity) -- The output stage needs to be a constant current source.

Precision constant current source circuit diagram