LED dimming engine: switch mode dimmable LED driver solution based on 8-bit MCU

Switch mode dimmable LED drivers are known for their high efficiency and precise control of LED current. This type of LED driver also provides dimming, allowing end users to reduce their power consumption while creating fantastic lighting effects. 8-bit microcontroller (MCU)-based solutions provide the necessary modules for such applications, enabling communication, customization, and intelligent control. In addition, integrated core-independent peripherals provide significant flexibility compared to pure analog or ASIC implementations, extending the functionality of lighting products while shaping product differentiation for innovation. This type of intelligent lighting solution with features such as fault prediction and maintenance, energy monitoring, color temperature maintenance, and remote communication and control is so numerous that it will be favored.

While LED drivers have many advantages over previous lighting solutions, there are many challenges in their implementation. But you don't have to worry, after reading this article, you will learn how to use 8-bit MCUs to easily address these design challenges, creating a high-performance switch-mode LED driver solution that is so rich that traditional solutions can only be seen .

The 8-bit microcontroller can independently control up to four LED channels, a unique capability not found in most off-the-shelf LED driver controllers. In Figure 1, the LED dimming engine can be constructed from peripherals provided in a microcontroller. These engines have separate, closed channels that require little or no central processing unit (CPU) intervention to control the switch mode power converter. This frees up the CPU to perform other important tasks, such as monitoring, communication, or new intelligence in the system.

Figure 1: Graphical representation of four LED strings controlled by Microchip's PIC16F1779 8-bit microcontroller

In Figure 2, the LED driver based on the current mode boost converter is controlled by an LED dimming engine. The engine is mainly independent of the core by complementary output generator (COG), digital signal modulator (DSM), comparator, programmable ramp generator (PRG), operational amplifier (OPA) and pulse width modulator 3 (PWM3). Peripheral (CIP) composition. These CIPs are combined with other on-chip peripherals such as fixed voltage regulators (FVRs), digital-to-analog converters (DACs), and capture/compare/PWM (CCP) to form a complete engine. The COG supplies a high frequency switching pulse to the MOSFET Q1 to transfer energy and supply current to the LED string. The switching period of the COG output is set by the CCP and duty cycle to maintain the constant current of the LED, depending on the comparator output. The comparator generates an output pulse whenever the voltage across Rsense1 exceeds the output of the PRG module. The input to the PRG is derived from the OPA output in the feedback circuit, which is configured as a slope compensator to counteract the effects of the intrinsic subharmonic oscillations when the duty cycle is greater than 50%.

The OPA module is implemented as an error amplifier (EA) with a Type II compensator configuration. The FVR is used as a DAC input to provide a reference voltage for the OPA non-inverting input based on the LED constant current specification.