This article originates from the technical feed of the electronics enthusiasts’ August theme month. Please indicate the source, and the author is Mark Pallones, an application engineer at the 8-bit microcontroller product department of Microchip Technology Inc.
Switch-mode dimmable LED drivers are renowned for their high efficiency and precise control of LED currents. They also offer dimming capabilities, enabling end-users to lower power consumption while achieving stunning lighting effects. Solutions based on 8-bit microcontrollers (MCUs) provide essential modules for such applications, facilitating communication, customization, and intelligent control. Furthermore, integrated core-independent peripherals offer significant flexibility compared to purely analog or ASIC implementations, enhancing the functionality of lighting products while fostering innovation through product differentiation. Such intelligent lighting solutions, featuring fault prediction and maintenance, energy monitoring, color temperature maintenance, and remote communication and control, will undoubtedly gain widespread favor.
Despite the numerous advantages of LED drivers over previous lighting solutions, implementing them presents several challenges. However, there’s no need to fret. By reading this article, you’ll learn how to leverage 8-bit MCUs to effortlessly overcome these design hurdles, creating a high-performance switch-mode LED driver solution that outshines traditional approaches.
The 8-bit microcontroller can independently control up to four LED channels, a distinctive capability rarely found in off-the-shelf LED driver controllers. As illustrated in Figure 1, the LED dimming engine can be built using peripherals provided within a microcontroller. These engines feature separate, closed channels that require minimal or no central processing unit (CPU) intervention to manage the switch-mode power converter. This allows the CPU to focus on other critical tasks, such as monitoring, communication, or introducing new intelligence into the system.
[Figure 1: Graphical representation of four LED strings controlled by Microchip's PIC16F1779 8-bit microcontroller]
**LED Dimming Engine**
In Figure 2, the LED driver based on the current-mode boost converter is controlled by an LED dimming engine. The engine primarily relies on core-independent peripherals (CIPs) 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 CIPs are combined with other onboard peripherals like fixed voltage regulators (FVRs), digital-to-analog converters (DACs), and capture/compare/PWM (CCP) to form a comprehensive engine. The COG provides a high-frequency switching pulse to the MOSFET Q1, transferring energy and supplying current to the LED string. The switching period of the COG output is set by the CCP and duty cycle to maintain the constant LED current, based 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, configured as a slope compensator to counteract the effects of intrinsic subharmonic oscillations when the duty cycle exceeds 50%.
The OPA module is implemented as an error amplifier (EA) with a Type II compensator configuration. The FVR serves as a DAC input, providing a reference voltage for the OPA’s non-inverting input based on the LED constant current specification.
This intelligent approach not only ensures efficient LED operation but also integrates advanced features, making it a standout choice for modern lighting systems. By understanding these mechanisms, designers can create robust, flexible, and future-proof lighting solutions tailored to diverse needs.
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