LED Driving Circuit with Pulse Transformer Isolation
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Solution Overview
Problem
Existing LED driving circuits face inefficiencies due to two-step voltage conversion and difficulty in distinguishing between normal and abnormal states during PWM operation, leading to poor power efficiency and inadequate circuit protection.
Innovation Solution
A driving circuit utilizing a single DC/DC converter with a pulse transformer for electrical isolation and a PWM dimming circuit that adjusts duty ratios to stabilize voltage, along with an abnormal state detection system involving a timer circuit to ensure accurate protection processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-step voltage conversion system is used (first DC/DC converter followed by second DC/DC converter), then electrical isolation between hot region and cold region is achieved, but power efficiency deteriorates
Solution Approach 1:
The patent merges the first DC/DC converter and second DC/DC converter into a single integrated converter that performs both voltage step-down and electrical isolation functions simultaneously. This eliminates the need for two separate conversion stages, thereby improving power efficiency while maintaining the required electrical isolation between hot and cold regions through internal circuit design.
Solution Approach 2:
The single DC/DC converter is designed to perform multiple functions: voltage step-down, electrical isolation, and feedback signal transmission. By making the converter universal and multi-functional, the system achieves the same performance as the two-step conversion system but with reduced energy loss and improved efficiency.
2Reliability
If a feedback line with photo coupler is used to maintain electrical isolation, then electrical isolation between hot region and cold region is maintained, but feedback precision deteriorates
Solution Approach 1:
The patent extracts the photo coupler from the feedback path and eliminates it entirely. Instead of using optical coupling, the system transmits feedback signals through galvanic isolation using the single DC/DC converter's control circuitry. This removal of the photo coupler eliminates the source of precision deterioration while maintaining electrical isolation through alternative means.
Solution Approach 2:
The patent introduces an intermediate control circuit within the single DC/DC converter that mediates the feedback signal transmission. This intermediate circuit provides galvanic isolation without requiring photo couplers, thereby maintaining both electrical isolation and feedback precision simultaneously through a different isolation mechanism.
3Use of energy by moving object
If PWM dimming operation is used to control LED luminance, then energy efficiency is improved, but ability to detect abnormal states deteriorates
Solution Approach 1:
The patent implements preliminary detection of abnormal states by monitoring LED forward voltage during the ON period of PWM operation. Before the PWM cycle completes and before normal operation resumes, the system checks for abnormal conditions such as open circuits or short circuits. This preliminary action allows detection of abnormalities while maintaining PWM energy efficiency.
Solution Approach 2:
The patent enhances feedback mechanisms to continuously monitor LED electrical characteristics during PWM operation. By implementing real-time feedback on forward voltage and current characteristics during both ON and OFF periods, the system can distinguish between normal PWM dimming states and actual abnormal conditions, thereby maintaining energy efficiency while improving detection capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances power efficiency by maintaining electrical isolation and effectively detects abnormal states, ensuring reliable circuit protection and improved LED operation.
Implementation Method 1
a pulse transformer (30) including a primary coil and a secondary coil
Data Source
AI summary
A pulse modulator generates a first pulse signal having a duty ratio which is adjusted such that a detection voltage which indicates the electrical state of an LED string to be driven matches a predetermined reference voltage. A first pulse signal is applied to a primary coil of a pulse transformer. A DC/DC converter includes a switching element the ON/OFF operation of which is controlled according to a signal that originates at a secondary coil of the pulse transformer. The DC/DC converter stabilizes an input voltage Vdc, and supplies the input voltage Vdc thus stabilized to the anode of the LED string.