This article is part of the technical content from the August issue of Elektor magazine. Please remember to cite the source. The author is Mark Pallones, an Application Engineer at the 8-bit Microcontroller Product Division of Microchip Technology Inc.
Switch-mode dimmable LED drivers are renowned for their high efficiency and precise control over LED currents. Such drivers also offer dimming capabilities, allowing end-users to reduce power consumption while achieving impressive lighting effects. Solutions based on 8-bit microcontrollers (MCUs) provide essential modules for these applications, facilitating communication, customization, and intelligent control. Furthermore, integrated core-independent peripherals give these solutions significant flexibility compared to purely analog or ASIC-based designs. This enhances the functionality of lighting products and helps manufacturers differentiate their offerings through innovative features. Intelligent lighting solutions with features like fault prediction, energy monitoring, color temperature management, and remote communication and control are becoming increasingly popular and will undoubtedly gain widespread adoption.
While LED drivers bring many advantages over traditional lighting solutions, implementing them presents several challenges. However, there’s no need to worry—after reading this article, you’ll understand how to leverage 8-bit MCUs to effortlessly overcome these design hurdles, creating a high-performance switch-mode LED driver solution that outshines conventional approaches.
The 8-bit microcontroller can independently manage up to four LED channels—a unique capability not commonly found in off-the-shelf LED driver controllers. As shown in Figure 1, the LED dimming engine can be constructed using peripherals available within a microcontroller. These engines consist of separate, self-contained channels that require minimal or no central processing unit (CPU) intervention to control the switch-mode power converter. This allows the CPU to focus on other critical tasks, such as monitoring, communication, or adding intelligence to the system.
Figure 1: Schematic representation of four LED strings controlled by Microchip's PIC16F1779 8-bit microcontroller
LED Dimming EngineIn Figure 2, the LED driver based on the current-mode boost converter is controlled by an LED dimming engine. This engine is largely independent of the core, comprising components such as the Complementary Output Generator (COG), Digital Signal Modulator (DSM), Comparator, Programmable Ramp Generator (PRG), Operational Amplifier (OPA), and Pulse Width Modulator 3 (PWM3). These Core-Independent Peripherals (CIPs) work together with other onboard peripherals like Fixed Voltage Regulators (FVRs), Digital-to-Analog Converters (DACs), and Capture/Compare/PWM (CCP) modules to create a complete system. The COG generates a high-frequency switching pulse that drives the MOSFET Q1 to transfer energy and supply current to the LED string. The switching period of the COG output is determined by the CCP and duty cycle settings, ensuring constant LED current based on the comparator’s output. The comparator outputs a pulse whenever the voltage across Rsense1 exceeds the PRG module's output. The PRG’s input comes from the OPA in the feedback loop, configured as a slope compensator to counteract inherent subharmonic oscillations when the duty cycle exceeds 50%.
The OPA module operates as an Error Amplifier (EA) with a Type II compensator configuration. The FVR serves as a DAC input to provide a reference voltage for the OPA’s non-inverting input, based on the specified LED constant current requirement.
As technology evolves, the integration of intelligent control into lighting systems continues to expand, offering endless possibilities for innovation and optimization. Whether it’s enhancing energy efficiency, improving user experience, or reducing maintenance costs, these solutions represent the future of smart lighting. With the help of 8-bit MCUs, designers can now achieve more sophisticated control over lighting systems, paving the way for smarter, greener, and more adaptive environments.
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