In the following circuit an LED is used to give a fixed reference voltage to a transistor. The output constant current I out is given by:
The LED lights up only when a load is connected at the output. Thus it indicates when the circuit is operating.
The operation of the circuit can be made clearer by re-arranging the components as follows:
The output will be limited to 100mA by using a red LED and 10R for Re.
The output will be limited to 500mA by using a red LED and 2R2 for Re.
The output will be limited to 1A by using a red LED and 1R0 for Re.
The LED lights up only when a load is connected at the output. Thus it indicates when the circuit is operating.
The operation of the circuit can be made clearer by re-arranging the components as follows:
The output will be limited to 100mA by using a red LED and 10R for Re.
The output will be limited to 500mA by using a red LED and 2R2 for Re.
The output will be limited to 1A by using a red LED and 1R0 for Re.
