LED Power Supply Dimming Control Circuit
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Solution Overview
Problem
In LED power supplies using PWM dimming, a small dimming ratio can result in an inductor current that fails to reach the desired level, leading to insufficient power supply to the LED load and abnormal operation due to decreased output voltage.
Innovation Solution
The proposed solution involves an LED power supply system with a converter, a dimming switch, and a driving control circuit that includes a feedback circuit, an enabling circuit, and a feedback loop control circuit. The enabling circuit generates an enable signal based on the feedback signal, a reference signal, and the PWM dimming signal, with the duty cycle of the enable signal adjusted to ensure the power switch is controlled effectively, synchronizing with the PWM dimming signal when the feedback signal is higher and increasing its duty cycle when the feedback signal is lower, thereby maintaining optimal output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PWM dimming signal with small duty cycle is used to control LED power supply, then power dissipation of power supply is decreased, but inductor current cannot increase from zero to desired level and output voltage decreases
Solution Approach 1:
The patent applies dynamics by making the power supply's response dynamic based on the dimming signal duty cycle. When the duty cycle is small, the system dynamically adjusts the inductor current to increase more rapidly, and extends the switching cycle period. This dynamic adaptation allows the system to maintain reliable output voltage under small dimming ratios while still achieving power dissipation reduction through PWM control.
Solution Approach 2:
The patent changes key parameters (inductor current increase rate and switching cycle period) based on the dimming signal characteristics. By detecting the small duty cycle of the PWM dimming signal, the system adjusts the inductor current slope and extends the switching period, thereby ensuring sufficient power delivery to the LED load even when the overall duty cycle is small, while maintaining the power-saving benefit of PWM dimming.
2Loss of energy
If PWM dimming signal with small duty cycle is used, then efficiency is improved, but power supplied to LED load is not high enough
Solution Approach 1:
The system dynamically adjusts the inductor current characteristics based on the dimming signal duty cycle. When a small duty cycle is detected, the inductor current is configured to increase more rapidly during the ON period, and the switching cycle period is extended. This dynamic parameter adjustment ensures that sufficient power is delivered to the LED load during the active period, maintaining efficiency while preventing power insufficiency.
Solution Approach 2:
The patent changes the inductor current slope and switching frequency parameters in response to small duty cycle dimming signals. By increasing the current rise rate and extending the overall period, the system ensures that the peak current and average power delivered to the LED load remain adequate, thus resolving the contradiction between efficiency improvement and sufficient power supply.
3Loss of energy
If inductor current is unable to increase from zero to desired level in one dimming cycle, then power dissipation is reduced, but LED load functions abnormally
Solution Approach 1:
The patent implements dynamic control where the inductor current behavior adapts to the dimming signal duty cycle. When the duty cycle is small, the system dynamically increases the inductor current slope and extends the switching period, ensuring that the current can reach the desired level within the available time. This maintains normal LED operation while preserving the low power dissipation benefit of small duty cycle PWM dimming.
Solution Approach 2:
The system changes the inductor current parameters (increase rate and achievable level) based on the dimming signal characteristics. By detecting when the duty cycle is too small for normal current buildup, the system adjusts the current slope and extends the switching period to ensure sufficient current reaches the LED load, preventing abnormal operation while maintaining energy efficiency.
Data Source
AI summary
A LED driving control circuit for controlling a power switch in a LED power supply includes: a feedback circuit coupled to a LED load and generating a feedback signal indicative of an output voltage of the LED power supply; an enabling circuit generating an enable signal according to the feedback signal, a first reference signal and a PWM dimming signal, wherein when the feedback signal is higher than the first reference signal, the enable signal synchronizes with the PWM dimming signal, and when the feedback signal is lower than the first reference signal, the duty cycle of the enable signal is higher than the duty cycle of the PWM dimming signal; and a feedback loop control circuit generating a control signal for controlling the power switch according to the feedback signal only when the enable signal is in an active state.