LED Average Current Regulation Circuit Using Feedback Control
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Solution Overview
Problem
Existing LED regulation techniques, such as floating buck regulators and modulation of reference voltage, struggle to accurately control average current due to loose parameters like inductance and switching frequency, leading to unpredictable and uncontrolled average current levels, and often require large space and limited switching frequency ranges.
Innovation Solution
A circuit and method for average-current regulation of LEDs that uses a regulator with an error amplifier and PWM comparator to control the path from LEDs to ground via a resistor, allowing for precise control of average current without the need for RC filters, reducing noise and power consumption, and enabling smaller form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If floating buck regulators in peak-current mode are used to control LEDs, then peak current is regulated, but average current becomes unpredictable and uncontrolled
Solution Approach 1:
The patent implements average current mode control with feedback by sensing the inductor current and using an error amplifier to compare the sensed average current with a reference current. The feedback loop continuously adjusts the PWM duty cycle to maintain the desired average current level, making average current predictable and controllable.
Solution Approach 2:
The patent replaces the mechanical/physical parameter dependency (inductance and switching frequency affecting peak-current mode behavior) with an electronic control system that directly measures and regulates average current through sensing and feedback, eliminating the unpredictable relationship between peak current and average current.
2Object-affected harmful factors
If RC filters are used to remove AC modulation in reference voltage, then AC components are filtered, but delay is introduced and switching frequency range is limited
Solution Approach 1:
The patent extracts and removes the RC filter component from the control loop by implementing average current sensing directly at the inductor current level. This eliminates the need for RC filtering of reference voltage, thereby removing the associated delay and switching frequency limitations while still achieving AC component rejection.
3Object-affected harmful factors
If RC filters are used to remove AC modulation, then AC components are removed, but switching frequency range becomes limited
Solution Approach 1:
The patent extracts and removes the RC filter component from the control loop by implementing average current sensing directly at the inductor current level. This eliminates the need for RC filtering of reference voltage, thereby removing the associated delay and switching frequency limitations while still achieving AC component rejection.
4Power
If conventional peak-current regulation is used, then peak current is controlled, but average current regulation is not achieved
Solution Approach 1:
The patent implements average current mode control with feedback by sensing the inductor current and using an error amplifier to compare the sensed average current with a reference current. The feedback loop continuously adjusts the PWM duty cycle to maintain the desired average current level, making average current predictable and controllable.
Solution Approach 2:
The patent replaces the mechanical/physical parameter dependency (inductance and switching frequency affecting peak-current mode behavior) with an electronic control system that directly measures and regulates average current through sensing and feedback, eliminating the unpredictable relationship between peak current and average current.
Data Source
AI summary
A regulator regulates one or more light emitting diodes (LEDs) so as to control an average current through the LEDs. The regulator could include a transistor switch that can couple the LEDs to ground. The regulator could also include circuitry that controls the transistor switch. The circuitry could use a substantially constant reference voltage to regulate the average current through the one or more LEDs. The transistor switch could couple the one or more LEDs to ground through a resistor, and the circuitry could include an error amplifier that compares the reference voltage to a voltage across the resistor. The circuitry could also include a gate driver that can drive a gate of the transistor switch. The error amplifier could be disabled for a period of time when the transistor switch is non-conductive, and the circuitry could include logic for enabling and disabling the error amplifier.