LED Control Circuit Reducing Current Peaks for EMC
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Solution Overview
Problem
Traditional LED control circuits face challenges with electromagnetic compatibility due to high current peaks and voltage variations, leading to unfavorable electromagnetic effects.
Innovation Solution
A control circuit that switches current between two values instead of completely turning it on and off, using a combination of first and second supply currents, with a conversion device to adjust current levels based on control signals, reducing current and voltage variations and lowering voltage load capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional PWM control switches current completely on and off, then LED brightness can be controlled, but high current peaks occur during switching which deteriorates electromagnetic compatibility
Solution Approach 1:
Instead of switching current completely on and off, the patent applies partial action by maintaining a non-zero baseline current while modulating the LED string with PWM signals. The supply device delivers a first supply current during on-periods and a second supply current (non-zero but lower) during off-periods, avoiding complete current interruption and thereby reducing electromagnetic interference while preserving brightness control capability
2Illumination intensity
If traditional control switches LED current completely on and off, then brightness control is achieved, but voltage peaks and current variations increase the voltage load requirement
Solution Approach 1:
The patent reduces voltage load by applying partial action - maintaining a non-zero second supply current during the off-period instead of complete current shutdown. This ensures the LED string continues to operate at reduced brightness without experiencing full supply voltage stress, thereby lowering the voltage load capacity requirements for the control circuit and supply device
Data Source
AI summary
A control circuit for control of light-emitting diodes has a first LED string (50) with at least one LED (51, 52, 53) and a first supply device (1) for supply of current to the first LED string (50). The supply device (1) has a control input (10) for delivery of a first control signal (CTL) and is provided for delivery, as desired, of a first supply current (IV1) or a second supply current (IV2) in dependence on the first control signal (CTL). The first and the second control currents (IV1, IV2) are non-zero.