Switching Regulator Control Circuit for LED Dimming EMI Reduction
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Solution Overview
Problem
Switching regulators face challenges in minimizing electromagnetic interference (EMI) and control loop overshoot when rapidly turning on and off LEDs, especially at low duty cycles, due to instantaneous current changes, which can cause visible flicker and EMI issues.
Innovation Solution
A switching regulator control circuit that slowly ramps the LED current up when turning on and down when turning off, using a ramped reference signal controlled by a capacitor and user-programmable rates, to alleviate EMI and overshoot, while maintaining good low duty cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the LED current is rapidly turned on and off to achieve PWM dimming, then the dimming control is effective and color shift is minimized, but electromagnetic interference (EMI) increases and control loop overshoot occurs
Solution Approach 1:
The patent applies preliminary action by ramping up the LED current gradually before the intended turn-on time and ramping down before the intended turn-off time. This pre-action approach prepares the current in advance to avoid abrupt changes, thereby reducing EMI while maintaining effective PWM dimming control and minimizing color shift.
2Illumination intensity
If the LED current is rapidly turned on and off to achieve PWM dimming, then the dimming control is effective, but visible flicker and audible noise occur
Solution Approach 1:
The patent uses preliminary action by gradually ramping up the LED current before the intended turn-on time and ramping down before the intended turn-off time. This pre-action approach eliminates abrupt current transitions that cause visible flicker and audible noise, while preserving effective PWM dimming control.
3Object-generated harmful factors
If the LED current is ramped up and down gradually, then EMI and control loop overshoot are reduced, but the dimming response time increases
Solution Approach 1:
The patent applies preliminary action by ramping up the LED current before the intended turn-on time and ramping down before the intended turn-off time. This pre-action approach reduces EMI and control loop overshoot while maintaining acceptable dimming response time, as the gradual transitions are timed to occur before the actual PWM switching events.
Solution Approach 2:
The patent employs dynamics by making the current transition rate adjustable through a programmable parameter. This allows the system to dynamically balance between EMI reduction and response time requirements, optimizing performance based on specific application needs.
4Speed
If a switch is introduced in series with the LEDs to enable faster turn on and turn off, then the turn off characteristic improves, but EMI issues are aggravated
Solution Approach 1:
The patent applies preliminary action by ramping up the LED current before the intended turn-on time and ramping down before the intended turn-off time. This pre-action approach reduces EMI and control loop overshoot while maintaining acceptable dimming response time, as the gradual transitions are timed to occur before the actual PWM switching events.
Data Source
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AI summary
A switching regulator control circuit includes a circuit configured to generate a control signal to control conduction of the regulator switch in response to a reference signal that is ramped to control a rate of change of the regulated output of the regulator and the control signal is gated in response to a PWM signal.