Single chip for LED bulbs that dim to lower CCT
Called iW3640, it is a 25W 2-channel mains-powered LED driver that needs no external microcontroller, and is intended for 75-150W-equivalent A19 and PAR bulbs, as well as 20-45W commercial dimmable external lighting ballasts.
There is a lot more iW3640 information on Electronics Weekly’s main news site.
It works by producing a PWM signal that gradually increases its duty-cycle as output current is reduced. A set of white LEDs is fed directly from the converter output (see diagrams below) while a set of amber LEDs is fed from the same output, but modulated by the PWM signal via a mosfet. In this way, the light output becomes more amber as the light is dimmed.
Tags: CCT, colour temperature, LED bulbs