LED Driver Current Control for Bus-Induced Flicker Suppression
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Solution Overview
Problem
Communication via a bus interface in lighting systems causes fluctuations in supply voltage, leading to visible changes in light emission due to changes in the current provided to lighting means, such as LEDs, resulting in flickering.
Innovation Solution
A control system that performs feedback and feedforward control of the current source using different gains based on the presence or absence of communication via the bus interface to stabilize the current and minimize light emission fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If communication is performed via the bus interface, then data transmission and control functions are enabled, but supply voltage fluctuations occur causing visible light emission changes
Solution Approach 1:
The control system applies preliminary anti-action by detecting communication events via the bus interface and preemptively adjusting the current source control parameters before voltage fluctuations can cause visible light emission changes. The system anticipates the harmful effect of voltage drops during communication and counteracts it by modifying the PWM duty cycle or current reference in advance, thereby preventing luminance variations rather than merely compensating for them after occurrence
Solution Approach 2:
The control system implements dynamics by dynamically adjusting the operating parameters of the current source based on the communication state. When communication is detected on the bus interface, the system transitions to a different operational mode with modified control parameters (such as adjusted PWM frequency or duty cycle limits) that are optimized to maintain stable light output despite voltage fluctuations. This dynamic adaptation allows the system to optimize performance for different operational conditions
2Reliability
If the current source responds to supply voltage changes, then electrical stability is maintained, but light emission fluctuations occur
Solution Approach 1:
The control system employs feedback mechanisms by continuously monitoring both the supply voltage and the actual light output (via current sensing or optical feedback). When voltage fluctuations are detected during communication events, the feedback loop adjusts the PWM duty cycle or current reference to compensate for the voltage change and maintain constant light output. This closed-loop control ensures that the harmful effect of voltage fluctuations on light emission is actively counteracted through real-time measurement and correction
Solution Approach 2:
The control system introduces an intermediary element - the PWM control signal or current reference - that mediates between the supply voltage and the lighting means. Instead of allowing the current source to respond directly to voltage changes (which causes light fluctuations), the PWM intermediary decouples this direct relationship by modulating the effective current based on the voltage conditions, thereby filtering out the harmful voltage variations while maintaining electrical stability
3Device complexity
If a single gain is used for feedforward control, then control simplicity is maintained, but light emission stability deteriorates during communication
Solution Approach 1:
The control system applies dynamics by making the feedforward control gain variable rather than fixed. The gain is dynamically adjusted based on the communication state detected via the bus interface - using a first gain value during normal operation and a second, differently optimized gain value during communication events. This dynamic gain adjustment allows the system to optimize light emission stability for different operational conditions without requiring a completely complex control architecture
Solution Approach 2:
The control system implements parameter changes by modifying the feedforward control gain parameter according to the communication state. When communication is detected on the bus interface, the system switches to a different gain parameter that is specifically optimized to compensate for voltage fluctuations during communication. This parameter adaptation allows the system to maintain simple control logic while achieving superior light emission stability under varying operational conditions
Data Source
AI summary
The invention relates to a control system (1) for controlling a current source (4) of an operating device (10) for lighting means (5). The current source (4) is configured to provide a current (ILM) to the lighting means (5). The operating device (10) comprises a bus interface (8) electrically connectable to a digital bus (7) and a voltage supply circuit (3) for providing a supply voltage (V1) to electrically supply the bus interface (8) and the current source (4). The control system (1) is configured to perform a feedback control of the current (ILM) with regard to a reference current (Iref1, Iref2), and determine whether a communication via the bus interface (8) is present or not. Further the control system (1) is configured to perform a feedforward control of the current (ILM) based on an error (EV) between the supply voltage (V1) and a reference voltage (Vref) for the supply voltage (V1), by processing the error (Ev) using a first gain (G1) in case the control system (1) determines that the communication is present and a second gain (G2) in case the control system (1) determines that the communication is not present. The first gain (G1) is different to the second gain (G2).