LED Driving Circuit Dynamic Reference Voltage Control
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Solution Overview
Problem
Existing LED driving circuits face challenges in precisely controlling the brightness of LED strings below a predetermined ratio due to limitations in reference voltage settings, where the upper limit reference voltage does not reach zero while the lower limit reference voltage does, making it difficult to adjust brightness effectively.
Innovation Solution
An LED driving circuit that generates a frequency modulation reference voltage and a compensation dimming signal to control the switching frequency and turn-on time of a power switch, using comparators and a set-reset flip-flop to manage the brightness based on sensing voltages and reference voltages, allowing for precise control of the LED string's brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper limit reference voltage is set above zero voltage with a predetermined margin, then the LED string can be protected from over-brightness, but the brightness cannot be controlled below a predetermined ratio
Solution Approach 1:
The patent applies dynamics by making the reference voltage dynamic rather than fixed. The reference voltage generator produces different reference voltages based on the dimming signal level: when the dimming signal is above a threshold, it generates a reference voltage with an upper limit above zero for protection; when the dimming signal is below the threshold, it generates a reference voltage that can reach zero to enable full dimming control. This dynamic adjustment resolves the contradiction between LED protection and full brightness control range.
Solution Approach 2:
The patent changes the parameter of reference voltage level based on operating conditions. By detecting the dimming signal level and switching between different reference voltage configurations (upper limit above zero vs. able to reach zero), the system adapts the reference voltage parameter to different brightness control requirements, thereby resolving the contradiction between protection and control range.
2Ease of operation
If the lower limit reference voltage is set to zero voltage, then full brightness ratio control is possible, but the upper limit reference voltage cannot provide adequate protection margin
Solution Approach 1:
The system dynamically switches between two reference voltage modes: in normal operation mode, the upper limit reference is set above zero for protection; in low-brightness mode, the reference voltage can reach zero for full control. This dynamic switching resolves the contradiction by applying the appropriate reference voltage configuration based on the current brightness requirement.
Solution Approach 2:
The patent implements preliminary action by proactively switching to a different reference voltage configuration before the brightness control problem occurs. When the dimming signal indicates low brightness requirement, the system preemptively switches to the zero-reachable reference voltage mode, ensuring that full dimming control is available when needed, while maintaining protection in normal operation modes.
3Device complexity
If a fixed reference voltage with upper limit is used, then the circuit structure remains simple, but the brightness control precision at low levels deteriorates
Solution Approach 1:
The reference voltage generator is made dynamic by adding a dimming signal level detection mechanism that automatically switches between different reference voltage configurations. This adds minimal complexity to the circuit while dramatically improving brightness control precision at low levels, as the system can use zero-reachable reference voltages when operating in low-brightness modes.
Solution Approach 2:
The patent changes the reference voltage parameter based on the dimming signal level. By detecting whether the dimming signal is above or below a threshold and accordingly generating different reference voltage characteristics, the system achieves high brightness control precision across the full range without requiring a completely complex circuit architecture.
Data Source
AI summary
A light emitting diode (LED) driving circuit disclosed herein controls a switching operation of a power switch connected to an LED string and includes a reference voltage generator configured to generate a frequency modulation reference voltage according to a dimming signal that controls brightness of the LED string, and a switching controller configured to control a switching frequency of the power switch to be constant when a level of the dimming signal is higher than that of the frequency modulation reference voltage, and control the switching frequency of the power switch based on the dimming signal when a level of the dimming signal is lower than that of the frequency modulation reference voltage.