When the blue LED was first created in the early 1990’s, it lead quickly to the creation of white LEDs, having finally conquered all the wavelengths needed to create a white light that could compete with CFLs and incandescent bulbs. LED’s significantly increased efficiency, life span, compared to the incandescent bulbs, and decreased hazardous waste, compared to CFLs, has seen LEDs become more and more popular in all lighting situations from television screens to home lighting. One particular benefit of LEDs is their ability to be dimmed easily and efficiently. However, without care, dimmed LEDs can flicker, which, at minimum, can be annoying. This flickering is also sometimes a sign that the LED’s are not being used to their full efficiency.
A subset of the RL78 family, the RL78/I1A, has been designed with the goal of creating microcontrollers that can easily and effectively provide efficient and dimmable LED control. These microcontrollers have high resolution PWMs to be able to control LEDs without any power-dissipative resistors or external constant current IC controllers. One of the methods of increasing the efficiency of controlling these LEDs is by actively correcting the power factor of the incoming signal. LEDs are a non-linear load due to their forward voltage, with the voltage increasing linearly but the current staying at zero until the forward voltage is crossed after which the current increases rapidly.
As seen below, with (a) being the ideal power factor and (b) as the reality of the non-linear LED loads, you can see how the RL78/I1A overcomes this problem with its power factor correction in (c). With peak and zero detectors, the RL78/I1A can track the voltage sinusoid of an incoming AC signal and create multiple current spikes within the sinusoid using the built-in 16-bit timers, to give a smoother current supply. This both creates a cleaner light with less flicker but also reduces the stress on the LEDs by keeping the current peaks well within operational limits.
Besides the built-in PFC modules, the RL78/I1A has other LED oriented modules including the the ability to detect overvoltage and overcurrent conditions and immediately turn off the output without CPU intervention. To allow for multiple, separately controlled LED chains using one microcontroller, there are six channels using the outputs of the four different 16-bit channels.
To achieve the greatest efficiency in LED lighting, both the power input and the power output must be looked at and balanced. With the RL78/I1A and its application note, found here - http://am.renesas.com/products/mpumcu/rl78/rl78i1x/rl78i1a/index.jsp you can produce custom LED lighting that is both beautiful and efficient.