LED Dimming Controller Decoupling Circuit for Flicker Reduction
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Solution Overview
Problem
Conventional LED dimming control circuits suffer from poor dimming linearity and flickering due to the limited driving ability of constant current drivers, particularly when the dimming ON period is short, leading to inadequate power delivery and slow current ramp-up.
Innovation Solution
The introduction of a decoupling circuit that defines a decoupling period at the start of the dimming ON period, allowing the compensation capacitor to hold its previous voltage, enabling the booster to deliver necessary power immediately and ensuring the PWM signal has a high duty cycle, thereby improving current sense and feedback voltage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the dimming ON period is shortened to achieve faster response time, then the response speed is improved, but the power delivery capability deteriorates and flickering occurs
Solution Approach 1:
The decoupling circuit performs preliminary action by holding the compensation capacitor voltage at a predetermined level during the decoupling period before the normal feedback control begins. This preliminary preparation ensures that when the dimming ON period starts, the system already has the necessary voltage head start, enabling immediate power delivery without waiting for the capacitor to charge from zero, thus resolving the contradiction between fast response and stable power delivery.
Solution Approach 2:
The control period is segmented into distinct phases: a decoupling period where the feedback circuit is disconnected from the compensation capacitor, and a normal control period where feedback control is active. This segmentation allows the system to perform different functions in different time windows - holding voltage during decoupling and regulating current during normal control - thereby achieving both fast response and stable power delivery.
2Measurement precision
If the compensation capacitor is continuously driven during dimming ON period, then the current regulation is improved, but the dimming linearity deteriorates
Solution Approach 1:
The decoupling circuit performs preliminary action by holding the compensation capacitor voltage at a predetermined level during the decoupling period before the normal feedback control begins. This preliminary preparation ensures that when the dimming ON period starts, the system already has the necessary voltage head start, enabling immediate power delivery without waiting for the capacitor to charge from zero, thus resolving the contradiction between fast response and stable power delivery.
Solution Approach 2:
The control period is segmented into distinct phases: a decoupling period where the feedback circuit is disconnected from the compensation capacitor, and a normal control period where feedback control is active. This segmentation allows the system to perform different functions in different time windows - holding voltage during decoupling and regulating current during normal control - thereby achieving both fast response and stable power delivery.
3Stability of the object's composition
If the feedback circuit continuously drives the compensation capacitor, then the voltage stability is improved, but the dimming response time increases
Solution Approach 1:
The decoupling circuit performs preliminary action by holding the compensation capacitor voltage at a predetermined level during the decoupling period before the normal feedback control begins. This preliminary preparation ensures that when the dimming ON period starts, the system already has the necessary voltage head start, enabling immediate power delivery without waiting for the capacitor to charge from zero, thus resolving the contradiction between fast response and stable power delivery.
Solution Approach 2:
The control period is segmented into distinct phases: a decoupling period where the feedback circuit is disconnected from the compensation capacitor, and a normal control period where feedback control is active. This segmentation allows the system to perform different functions in different time windows - holding voltage during decoupling and regulating current during normal control - thereby achieving both fast response and stable power delivery.
Data Source
AI summary
Disclosed are LED controllers for dimming. An LED controller includes a current driver, a pulse-width modulator, a feedback circuit, and a decoupling circuit. The current driver, selectively in response to a dimming signal, causes a driving current flowing through one LED string. The dimming signal is capable of defining a dimming ON period and a dimming OFF period. The pulse-width modulator generates a PWM signal to control a power switch, in order to buildup a driving voltage at a power node of the LED string. The PWM signal is generated in response to a compensation signal. The feedback circuit, based upon a feedback voltage from the light emitting device, drives a compensation capacitor to generate the compensation signal. The decoupling circuit defines a decoupling period at the start of the dimming ON period and causes the feedback circuit not driving the capacitor during the decoupling period.