Low-Headroom LED Driver Circuit for Boost-Ripple Cancellation
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Solution Overview
Problem
Existing LED driver circuits suffer from reduced efficiency and inability to effectively cancel boost converter ripple, leading to variations in LED operating current due to insufficient loop bandwidth and non-linear voltage drops across LED stacks.
Innovation Solution
Implement a multi-path controller with a feedforward and high-frequency feedback mechanism to set a target DC component of the load current and compensate for converter output voltage ripple, using a current sensing circuit and supply ripple compensator to cancel a portion of the ripple waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a boost converter is used to generate power supply voltage for LED stack, then the power supply voltage is sufficient to drive the LED stack, but the output voltage contains ripple that causes current variation in the LED
Solution Approach 1:
The patent implements a feedback mechanism where the output current is sensed and fed back to the multi-path controller. The controller uses this feedback to adjust the driver stage and compensate for ripple-induced current variations, thereby maintaining constant LED current despite the presence of boost converter output voltage ripple.
Solution Approach 2:
The patent introduces a multi-path controller as an intermediary between the boost converter and the LED driver stage. This controller processes both the power supply voltage and the output current feedback, generating control signals that adjust the driver stage to cancel out the harmful ripple effects before they reach the LED stack.
2Loss of energy
If the voltage drop across the driver transistor is maintained at a low value for efficiency, then energy loss is reduced, but the loop bandwidth is insufficient to cancel ripple at the switching frequency
Solution Approach 1:
The patent segments the control function into multiple independent paths within the multi-path controller. One path handles the DC component control with low bandwidth requirements, while another path specifically handles the ripple cancellation at switching frequency. This segmentation allows each path to be optimized independently, enabling efficient ripple rejection without requiring the entire control loop to operate at high bandwidth.
Solution Approach 2:
The patent applies partial action by implementing a dedicated high-frequency feedback path that operates specifically at the switching frequency to cancel ripple. Rather than requiring the entire control loop to operate at high bandwidth, only the necessary ripple cancellation function operates at high frequency, while the main DC control operates at lower bandwidth, thus maintaining efficiency.
3Measurement precision
If a current-output DAC and reference current mirror are used to control LED current, then the DC value of output current is well-controlled, but the circuit complexity increases and efficiency decreases due to headroom requirements
Solution Approach 1:
The multi-path controller performs multiple functions within a single integrated circuit block: it generates the control signal for the driver stage, processes output current feedback, cancels ripple at switching frequency, and regulates the DC component of the LED current. This multi-functionality eliminates the need for separate control circuits, thereby reducing overall system complexity while maintaining precise current control.
Data Source
AI summary
A driver circuit provides a load current to a light-emitting diode (LED) or other load, includes a driver stage having an output coupled to the light-emitting diode and having a power supply input for receiving input current having a DC component and a converter output voltage ripple waveform component. A multi-path controller sets a target value of the DC component of the load current according to a control value from a feedforward path and controls the DC component of the load current with a low-frequency feedback path and compensates for the converter output voltage ripple waveform component with a high-frequency feedback path to cancel at least a portion of a component of the converter output voltage ripple waveform conducted from the driver stage to the load. A current sensing circuit may provide a measure of the load current and the controller may implement a supply ripple compensator.