Synchronous Flyback LED Driver With Primary-Side Voltage Feedback
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Solution Overview
Problem
Conventional synchronous flyback converters face challenges in accurately controlling the secondary side voltage for LED loads due to significant voltage drops across diodes and difficulties in feeding back feedback signals across the galvanic isolation, leading to inefficiencies and inaccurate LED current control.
Innovation Solution
A synchronous flyback converter with a sensing winding and a control unit on the primary side that uses feedback signals derived from the sensing voltage to control the frequency and duty cycle of the primary side switch, allowing for closed-loop control of the secondary side voltage by sampling the sensing voltage during specific switch-on cycles and compensating for resistive elements, enabling accurate LED voltage measurement and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensing winding is coupled to the primary winding and feedback is taken during secondary switch conduction, then LED voltage measurement accuracy improves, but voltage drops across resistive elements contaminate the measurement
Solution Approach 1:
The patent applies preliminary action by sampling the sensing voltage at a specifically predetermined time point during the secondary switch conduction cycle. This timing is chosen to minimize the influence of resistive voltage drops, effectively capturing the LED voltage before significant resistive losses occur. The control unit is configured to sample at this optimal moment, thereby achieving accurate LED voltage measurement while avoiding contamination from resistive elements.
2Loss of energy
If synchronous rectification with FET transistors is used instead of diodes, then conduction losses are reduced, but device complexity increases
Solution Approach 1:
The patent applies mechanics substitution by replacing the passive diode rectification system with an active synchronous rectification system using FET transistors. This substitution replaces a simple mechanical/electrical component (diode) with a controllable semiconductor device that can be actively managed by the control unit. The FETs are controlled to conduct during specific phases, achieving lower conduction losses compared to diode rectification, while the control unit manages the increased complexity through coordinated switching signals.
3Measurement precision
If feedback signals are taken from the secondary side, then closed-loop control accuracy improves, but galvanic isolation requirements increase system complexity
Solution Approach 1:
The patent applies the intermediary principle by using the sensing winding coupled to the primary winding as a mediator to obtain feedback information about secondary side conditions. Instead of directly sensing secondary side voltages or currents, the system uses the sensing winding on the primary side to indirectly detect the state of the secondary circuit through electromagnetic coupling. This intermediary approach allows accurate feedback while maintaining galvanic isolation, as the sensing winding provides indirect information without requiring direct electrical connection across the isolation barrier.
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 solution reduces voltage drops and improves the accuracy of LED voltage measurement and control, enhancing the efficiency and performance of the converter by minimizing the influence of resistive elements and allowing for precise light control, while being cost-effective by eliminating the need to cross the galvanic isolation barrier.
Implementation Method 1
a sensing winding coupled to a primary winding of a transformer of the flyback converter
Data Source
AI summary
The invention relates to a synchronous flyback converter (100) having terminals for supplying an LED load. The synchronous flyback converter (100) comprises a sensing winding (Lw) coupled to a primary winding (Lp) of a transformer T of the flyback converter (100), a control unit (106) controlling a primary side switch (S1) in series to the primary winding (Lp) of the flyback converter (100) using a feedback signal for a closed loop control of a secondary side voltage of the flyback converter (100) by controlling the frequency and/or duty cycle of the switching of the primary side switch (S1), wherein the feedback signal is derived from a sensing voltage across the sensing winding (Lw) sampled once during a switch-on time of a secondary side switch (S2) of the flyback converter (100).