LED Driver Dimming Circuit Using Differential Feedback Control
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Solution Overview
Problem
Existing LED drivers lack a dimming capability, particularly when using a general-purpose boost converter controller IC with a fixed internal reference voltage, which is not suitable for series-connected LEDs.
Innovation Solution
A single stage AC input boost converter LED module with a differential amplifier coupled to a variable dimming voltage and a resistor connected to the cathode of an LED array, along with a controller having an error amplifier to regulate the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LED current is reduced to dim the LED, then power consumption decreases, but the forward voltage of the LED increases making dimming difficult
Solution Approach 1:
The patent introduces a boost converter circuit as an intermediary between the power source and LED to manage the voltage-current relationship. The boost converter stores energy in an inductor and releases it to maintain constant LED current despite increasing forward voltage, enabling efficient dimming while compensating for voltage changes
Solution Approach 2:
The patent changes the operating parameters of the LED driver by switching from constant current mode to constant power mode at low dimming levels. The controller dynamically adjusts the duty cycle and switching frequency to maintain constant power delivery, which compensates for the increasing forward voltage and enables precise dimming control
2Reliability
If separate circuits are used for constant current LED driver and constant power dimming control, then each function can be optimized, but device complexity increases
Solution Approach 1:
The patent merges the constant current LED driver and constant power dimming control into a single integrated circuit. The controller combines the boost converter control, current regulation, and power management functions in one device, reducing component count and simplifying the overall system while maintaining both constant current and constant power capabilities
Solution Approach 2:
The integrated controller is designed to perform multiple functions: it operates as a constant current driver at high brightness levels and automatically transitions to constant power mode at low brightness levels. The single device handles both LED forward voltage compensation and dimming control, eliminating the need for separate dedicated circuits
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient dimming of LEDs by varying the output voltage and current, effectively controlling the brightness of the LEDs while maintaining a stable output voltage.
Implementation Method 1
a boost converter circuit including an inductor coupled between the power source and the LED
Implementation Method 2
light emitting diode (LED)
Implementation Method 3
produce a light output
Data Source
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AI summary
Embodiments include systems, methods, and apparatuses for providing a dimming function in a single stage AC input light emitting diode (LED) driver with a controller that contains an on-chip error amplifier and an on-chip fixed reference voltage source coupled to a first input of the error amplifier. The controller controls a duty cycle of a switching transistor to cause a feedback voltage, applied to a first package input terminal, to match the reference voltage. To achieve a dimming function, a voltage across a current sense resistor in series with the LEDs is applied to a first input of a high gain differential amplifier, and a variable dimming control voltage is applied to a second input of the differential amplifier. The output of the differential amplifier is coupled to the first package input terminal. The differential amplifier input signals will be matched at the target LED current level.