Probably everybody knows that LEDs don’t like current changes, so how to deal with this and avoid damages? One solution could be a circuit that provides a constant current despite variations of the input voltage.
For instance, this circuit can take up to 300mA and up to 40V and provide a voltage that is necessary for one LED. Circuit can be adapted for a single LED running from 3.5V or several LEDs like three connected in series. Then Circuit provides about 10V. More LEDs are used more heat is generated – heat sink is necessary in this case to avoid transistor overheats. This simple circuit is available as a kit for only $9.85. But probably it could be built quickly by electronics entrepreneur. [Source]
