Primary-Side Isolated Flyback Converter for LED Drivers
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Solution Overview
Problem
Isolation-type LED lamp driver circuits using flyback converters require additional secondary-side current sensor circuits and insulation elements, leading to increased system volume and manufacturing costs, necessitating a method to control secondary-side current without these components while maintaining stability and improving power factor.
Innovation Solution
An isolated flyback converter for LED drivers that employs primary-side control, utilizing a snubber circuit, switching unit, and control unit to detect and regulate power supply voltage fluctuations, eliminating the need for secondary-side current sensors and insulation elements like opto-couplers, and includes components such as peak voltage detectors, operational amplifiers, multipliers, and latch circuits to maintain constant secondary-side current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional secondary-side current sensor circuits and insulation elements are used in isolation-type LED driver circuits, then current control stability is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent extracts and eliminates the secondary-side current sensor circuit and opto-coupler from the traditional isolation-type LED driver circuit. By using primary-side regulation, the control is achieved without these additional components, reducing circuit complexity while maintaining current control stability through voltage detection and control on the primary side.
Solution Approach 2:
The controller on the primary side performs multiple functions: it detects input voltage, detects output voltage through the transformer, regulates current, and provides isolation. This multi-functional approach replaces the need for separate secondary-side sensing and isolation components, achieving both simplified circuitry and reliable control.
2Reliability
If additional secondary-side current sensor circuits and insulation elements are used in isolation-type LED driver circuits, then current control stability is improved, but manufacturing costs increase
Solution Approach 1:
The patent removes expensive components such as secondary-side current sensors and opto-couplers from the circuit. By implementing primary-side regulation, the design eliminates these costly parts while maintaining current control stability, thereby reducing manufacturing costs.
Solution Approach 2:
The patent uses simpler, less expensive components on the primary side to achieve the same control function. The primary-side regulation approach uses basic voltage detection and control circuits instead of expensive secondary-side sensing components, making the overall system more cost-effective.
3Device complexity
If primary-side control is used without secondary-side circuits, then device complexity is reduced, but current control precision may worsen
Solution Approach 1:
The patent implements feedback control on the primary side by detecting the output voltage through the transformer and comparing it with a reference voltage. The controller adjusts the switching duty cycle based on this feedback to maintain precise current control, achieving both simplified circuitry and high precision through intelligent control algorithms.
Solution Approach 2:
The patent replaces direct secondary-side current sensing with primary-side voltage detection and control. By using electrical field coupling through the transformer and sophisticated control algorithms, the system achieves precise current regulation without mechanical or direct electrical contact on the secondary side, maintaining precision while reducing complexity.
4Reliability
If opto-couplers are used for insulation, then electrical isolation is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the opto-coupler from the circuit by implementing primary-side regulation. The transformer provides inherent galvanic isolation, and the controller achieves communication and control through this isolation barrier without requiring additional opto-coupling components, thereby reducing circuit complexity while maintaining electrical isolation.
5Reliability
If opto-couplers are used for insulation, then electrical isolation is improved, but manufacturing costs increase
Solution Approach 1:
The patent removes the expensive opto-coupler component by using primary-side regulation. The transformer's inherent isolation capability combined with primary-side control eliminates the need for additional isolation components, reducing bill of materials cost and simplifying manufacturing while maintaining electrical isolation reliability.
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
Enables stable control of secondary-side current and improved power factor in LED drivers without additional secondary-side circuits, reducing costs and system volume while maintaining control over LED load and power supply fluctuations.
Implementation Method 1
energy is stored in a magnetizing inductance on the primary side of a transformer while a switch is turned on, and energy in the magnetizing inductance is transmitted to an LED load on the secondary side of the transformer when the switch is turned off
Implementation Method 2
it may be necessary to use an element (e.g. an opto-coupler), which transmits a signal through light that is used to give feedback to drive the current
Data Source
AI summary
An isolated flyback converter for an LED driver may include: (1) A snubber circuit configured to be connected to the primary side of a transformer. (2) A switching unit configured to have a source terminal and a drain terminal and configured to be turned on or off. (3) A control unit configured to detect a first input signal proportional to a fluctuation in the power supply voltage, detect a second input signal when the switching unit is turned off, generate a signal inversely proportional to the maximum value of the first input signal and multiply the generated signal to the second input signal, and control a peak current of the switching unit to be proportional to the multiplication result of the signal inversely proportional to the maximum value of the first input signal and the second input signal such that a secondary-side current of the transformer is maintained constant.