Single-Stage LED Driver Dimming via Differential Amplifier Feedback
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Solution Overview
Problem
Conventional LED drivers lack dimming capability and are not suitable for applications requiring control over brightness, especially when using series-connected LEDs with high voltage drops, as they rely on fixed internal reference voltages that do not allow for adjustable current control.
Innovation Solution
A module with a resistor connected to the cathode of LEDs, a differential amplifier, and a controller that adjusts the output voltage by turning a switching transistor on and off, using a variable dimming voltage to regulate the current through the LEDs, allowing for adjustable brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed internal reference voltage is used in the controller, then the circuit design is simplified, but dimming capability is lost
Solution Approach 1:
A differential amplifier is introduced as an intermediary component between the fixed internal reference voltage and the LED driver circuit. The differential amplifier compares the fixed reference voltage with a variable dimming control voltage, generating an error signal that adjusts the LED drive current. This mediator enables dimming functionality without modifying the fixed internal reference voltage source, thus maintaining controller simplicity while adding adaptability.
2Illumination intensity
If the drive current through LEDs is reduced to dim them, then brightness is controlled, but the non-linear load characteristics make current regulation difficult
Solution Approach 1:
A feedback mechanism is implemented where the drive current through the LEDs is sensed (via a sense resistor connected to the cathode), converted to a voltage signal, and fed back to the differential amplifier. The differential amplifier continuously compares this feedback signal with the dimming control voltage and adjusts the drive current accordingly. This closed-loop feedback system simplifies current regulation despite the non-linear characteristics of LED loads.
3Power
If series-connected LEDs with high voltage drops are used, then the lighting output is increased, but the available voltage headroom for control is reduced
Solution Approach 1:
The patent replaces voltage-based control mechanisms with current-based control. Instead of attempting to control LED brightness by adjusting voltage (which is difficult with series-connected high-voltage-drop LEDs), the system controls the drive current through the LEDs. The differential amplifier regulates current by comparing a sense voltage (proportional to current) with the dimming control voltage, eliminating the need for voltage headroom and enabling effective dimming of series-connected LEDs.
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 effective dimming of LEDs by varying the current, improving brightness control and efficiency while maintaining a stable output voltage, even with high voltage drops across series-connected LEDs.
Implementation Method 1
A voltage across the resistor may be proportional to a current through the one or more LEDs. The module may include a differential amplifier. A first input of the differential amplifier may be coupled to the voltage across the resistor and a second input of the differential amplifier may be coupled to a variable dimming voltage
Implementation Method 2
The module may include a switching transistor coupled to the controller. The controller may turn the switching transistor on and off based on an output of the differential amplifier to vary the output voltage and the current through the one or more LEDs
Implementation Method 3
A voltage across the resistor may be proportional to a current through the one or more LEDs
Data Source
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.