The BCR320U/BCR321U can serve as an easy-to-use, constant current source for LEDs. In stand alone applications, an external resistor can be connected to adjust the current from 10 mA to 250 mA. In the case of using the BCR420U/BCR421U, the output current is adjustable between 10 mA and 150 mA. An additional feature of the BCR321U and BCR421U devices is that they have an enable pin that can be connected to a Microcontroller for dimming of the LEDs with PWM. When using these application circuits, Rext can be determined by using the diagram 'Output current versus external resistor‘ in the appropriate datasheet. Please take into account that the resulting output currents will be slightly lower due to the self heating of the component and the negative thermal coefficient.