This LM317 constant current source circuit is using transistors and can be used as a driver for LED strings. The following LM317 constant current source circuit is splitting up the current sense resistor into three resistors, one for each leg of the LED string.
Current through any one of the LED strings of LM317 constant current source circuit is set using this equation: Iout= (1.25V+ Vsat)/Rsense .
Vsat is saturation voltage for transistor used in circuit .
When the circuit works properly all the LEDs are running, all three sense resistors have about 1.25 V across
This bicolor led driver circuit allow driving a bicolor LED that changes color light depending on the supply voltage. When voltage control circuit input range from 0 V to +12 V LED lights green at first and then pass gradually through orange and yellow to red.
The supply voltage for this bicolor led driver circuit must not exceed 30 V when more than 12 V, the values of resistors R7 and R8 should be changed accordingly.