LED Circuit Average Current Control via PWM Modulation
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Solution Overview
Problem
Conventional buck type LED circuits face challenges in accurately controlling the average current to the LED, with Method 1 experiencing high error due to ripple in peak current mode control and Method 2 introducing additional power loss with a series coupled current sense resistor.
Innovation Solution
A circuit comprising a sense unit, compensation unit, and modulate unit that uses mid-current sense or full-wave sense methods to accurately regulate the average current, employing an operational amplifier and RC filter for compensation and a PWM modulator to adjust the main switch's ON/OFF time based on sensed and reference signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If peak current mode control is used to regulate current, then the control method is simple with no external circuit needed, but the average current control precision is low due to ripple influence
Solution Approach 1:
The patent introduces a current sense resistor as an intermediary element to detect the actual average current flowing through the LED. This mediator enables precise measurement without requiring complex control circuits, resolving the contradiction between simplicity and precision by using a straightforward sensing approach combined with PWM modulation.
Solution Approach 2:
The patent replaces the traditional peak current mode control mechanism with a PWM-based average current control system. Instead of controlling peak current directly, the system uses pulse width modulation to control the average current, substituting the control approach to achieve both simplicity and high precision simultaneously.
2Measurement precision
If a series coupled current sense resistor is used to detect LED current, then average current control precision is high, but additional power loss is introduced
Solution Approach 1:
The patent optimizes the resistance value of the current sense resistor to minimize power loss while maintaining measurement precision. By carefully selecting the resistance parameter, the system achieves high precision average current control without introducing significant power loss, resolving the contradiction through parameter optimization.
3Device complexity
If conventional current control methods are used, then the circuit structure remains simple, but brightness regulation precision is insufficient
Solution Approach 1:
The patent implements a feedback control mechanism where the current sense resistor continuously monitors the average current and feeds this information back to the control circuit. This feedback loop enables precise brightness regulation by adjusting the PWM duty cycle based on actual current measurements, achieving high precision without complicating the overall circuit structure.
Data Source
AI summary
An LED circuit is disclosed. The circuit senses the average current flowing through the LED. The sensed signal is compensated and modulated. The modulated signal is then used to control the ON/OFF state of a switch that supplies power to the LED.