Could be done but voltage regulators just burn a bunch of energy which doesnt seem very smart for a mobile device. Also if you already need a transistor for switching the LED then just picking one that can do so at 200Hz or more is gonna save you an extra part and give you much finer and easier control over dimming.
Why would they use PWM to drive an LED in a DC circuit when they could just drop the voltage to make it dimmer?
Could be done but voltage regulators just burn a bunch of energy which doesnt seem very smart for a mobile device. Also if you already need a transistor for switching the LED then just picking one that can do so at 200Hz or more is gonna save you an extra part and give you much finer and easier control over dimming.