LED Current Source Control Using Reference Modulation Against EMI Flicker
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Solution Overview
Problem
Existing control systems for current sources providing current to lighting means, such as LEDs, suffer from electromagnetic interference (EMI) causing sudden flickering, which is not effectively mitigated by existing methods that require modulation frequencies above the control system's corner frequency, leading to instability and visibility of flickering.
Innovation Solution
A control system that modulates the reference current with a frequency below the control system's corner frequency by generating a second reference current with an amplitude that periodically changes, allowing for EMI mitigation without requiring modulation frequencies above the corner frequency, thereby stabilizing light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the output of the feedback control is periodically changed with a frequency above the visible light flicker spectrum to mitigate EMI, then the sudden flickering caused by EMI is prevented, but the frequency requirement conflicts with the control system's corner frequency leading to instability
Solution Approach 1:
The patent applies preliminary action by modulating the reference current before it enters the feedback control loop. This pre-modulation of the reference current with a triangular waveform introduces the desired periodic variation that counters EMI effects, while allowing the feedback control to operate stably at its corner frequency without conflict
2Object-affected harmful factors
If the modulation frequency is set above the control system's corner frequency to achieve EMI mitigation, then flickering is reduced, but the control system becomes unstable and flickering becomes visible
Solution Approach 1:
The reference current is pre-modulated with a triangular waveform before being processed by the feedback control system. This preliminary modulation establishes the frequency characteristics needed to prevent visible flickering, while the feedback control operates stably within its designed frequency range
Solution Approach 2:
The patent introduces dynamic modulation of the reference current using a triangular waveform with a specific frequency range (100 Hz to 10 kHz). This dynamic variation in the reference current creates a corresponding dynamic response in the light emission that prevents perceivable flickering while maintaining system stability
3Object-affected harmful factors
If a modulator is introduced to modulate the feedback control output, then EMI mitigation is achieved, but the device complexity increases
Solution Approach 1:
Instead of modulating the output of the feedback control as in conventional approaches, the patent pre-modulates the reference current input to the feedback control. This shifts the modulation function to the input stage, simplifying the overall system architecture while achieving the same EMI mitigation effect
Solution Approach 2:
The patent changes the approach from output modulation to input modulation by varying the reference current parameters. This parameter change at the input stage achieves EMI mitigation without requiring complex output modulation circuits, thereby reducing device complexity
Data Source
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AI summary
The invention relates to a control system (1) for controlling a current source (7) configured to provide a current (ILM) to lighting means (8). The lighting means are optional at least one light emitting diode (LED). The control system (1) is configured to obtain a first reference current (Iref1) for the current (ILM) and generate, based on the first reference current (Iref), a second reference current (Iref2), wherein an amplitude of the second reference current (Iref2) periodically changes, with a frequency, around an amplitude of the first reference current (Iref1). Further, the control system (1) is configured to perform a feedback control of the current (ILM) with regard to the second reference current (Iref2). The invention further relates to an operating device (13) for lighting means (8), comprising such a control system (1); a luminaire (14) comprising such an operating device (13); and a method for controlling a current source.