English: Electronic circuit schematic for a current limiter or current source.

An issue with the circuit here:Current_limiting_using_bjt.gif , is that Q1 will not be saturated unless its base is biased about 0.5 volts above Vcc.

This circuit operates more efficiently from a single (Vcc) supply.

In this circuit, R1 allows Q1 to turn on and pass voltage and current to the load. When the current through R_sense exceeds the design limit, Q2 begins to turn on, which in turn begins to turn off Q1, thus limiting the load current. The optional component R2 protects Q2 in the event of a short-circuited load. When Vcc is at least a few volts, a MOSFET can be used for Q1 for lower dropout-voltage. Due to its simplicity, this circuit is sometimes used as a current source for high-power LEDs.