LED Driving Device Overvoltage Protection and Duty Control
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Solution Overview
Problem
Conventional LED driving circuits employing boost type DC-DC converters face challenges in overvoltage protection and perfect duty control, particularly with current-mode PWM driving ICs, where the duty of the output signal does not reach 0%, causing LEDs to remain slightly lit when turned off and requiring separate circuits for different color LEDs, which complicates brightness and color control.
Innovation Solution
An LED driving device with overvoltage protection and duty control functions, incorporating a PWM IC that generates a sawtooth wave voltage, a voltage comparator, and a switching portion to ensure the duty of the output signal is perfectly 0% by using a sawtooth wave voltage comparison and a switching mechanism to control the LED array's voltage, and includes a voltage detector and comparator to manage overvoltage and dimming signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a current-mode PWM driving IC is used to control LED brightness, then the brightness control is achieved, but the duty of the output signal cannot reach 0% causing LEDs to remain slightly lit
Solution Approach 1:
The patent introduces a voltage comparator as an intermediary component between the PWM IC and the LED array. The comparator compares the PWM output voltage with a reference voltage and generates a corrected drive signal that can achieve true 0% duty cycle by completely cutting off the LED current when the PWM signal is off, eliminating the residual illumination caused by direct PWM IC output.
2Power
If a boost type DC-DC converter is used to drive LED array, then the voltage conversion is achieved, but overvoltage may damage the LED and driving circuit when load is open or inductor voltage increases
Solution Approach 1:
The patent implements a feedback mechanism using a voltage detector that continuously monitors the LED array voltage and feeds this information back to the control circuit. When overvoltage is detected (such as when LED load is open or inductor voltage spikes), the feedback signal triggers the voltage comparator to cut off the drive signal, preventing damage to the LED and driving circuit while maintaining normal boost operation under normal conditions.
3Adaptability or versatility
If separate driving circuits are used for different color LEDs, then each color LED can be driven independently, but the device complexity increases and brightness/color control becomes difficult
Solution Approach 1:
The patent employs a universal driving circuit design where a single boost type DC-DC converter and PWM control system can drive LED arrays of different colors (red, green, blue). The circuit achieves color control through PWM duty cycle modulation of a common drive signal, eliminating the need for separate driving circuits for each color while maintaining the ability to independently control brightness and color coordinates through software or control signals.
Data Source
AI summary
An LED driving device comprises a PWM IC including an RT/CT terminal operated by a power voltage and generating and outputting a sawtooth wave voltage of a predetermined frequency, a COMP terminal to which a comparison voltage compared with the sawtooth wave voltage is inputted, and an output terminal generating and outputting a pulse signal turned off in a section in which a level of the sawtooth wave voltage is higher than a level of the comparison voltage and turned on in a section in which the level of the sawtooth voltage is lower than the level of the comparison voltage. The LED driving device sets up the comparison voltage inputted to the COMP terminal of the PWM IC to be 0 when an error voltage corresponding to a difference between a both end voltage of an LED array and a predetermined reference voltage is less than a predetermined level.