LED Power Supply Control Circuit Using Transformer Feedback
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Solution Overview
Problem
Existing power supply devices for LEDs face challenges in precisely controlling switching frequency on the primary side without using expensive or complex circuits, particularly due to the reliance on photo couplers for feedback information transfer, which increases manufacturing costs and complicates circuit design.
Innovation Solution
A control circuit that generates a PWM signal to control the switching frequency of the primary side based on feedback information from the secondary side, utilizing a dimming unit, current generating unit, signal generating unit, and driving unit to maintain a constant voltage difference between minimum and maximum voltage levels, thereby simplifying the circuit and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a photo coupler is used to transfer feedback information from secondary side to primary side, then insulating function is improved, but manufacturing cost increases and circuit design becomes difficult
Solution Approach 1:
The patent extracts the feedback information transfer function from the primary side and relocates it to the secondary side. The feedback circuit is completely removed from the primary side, eliminating the need for photo couplers and their associated complexity while maintaining electrical insulation through the transformer's magnetic coupling.
Solution Approach 2:
The transformer serves multiple functions: power transformation, electrical insulation, and feedback information transfer. By utilizing the transformer's magnetic coupling for both power and feedback signals, the patent eliminates the need for separate photo coupler components while maintaining insulating functionality.
2Reliability
If photo coupler is used for feedback information transfer, then insulating function is improved, but manufacturing cost increases
Solution Approach 1:
The patent removes the expensive photo coupler component from the circuit by extracting its feedback transfer function and implementing it through the transformer's magnetic coupling on the secondary side, thereby reducing component count and manufacturing cost.
Solution Approach 2:
The patent uses the transformer's magnetic field as a copy mechanism to transfer feedback information across the insulation barrier, replacing the need for physical photo coupler components while maintaining the insulating function.
3Device complexity
If power switching control circuit and driving circuit are both formed on secondary side, then photo coupler is eliminated, but switching frequency control precision deteriorates
Solution Approach 1:
The patent segments the control functions by placing the power switching control circuit on the primary side and the driving circuit on the secondary side. This segmentation allows precise switching frequency control on the primary side while maintaining the benefit of having the driving circuit on the secondary side.
Solution Approach 2:
The patent implements a feedback mechanism where feedback information about the power state is transferred from the secondary side to the primary side through the transformer's magnetic coupling, enabling precise switching frequency control based on real-time power state information.
Data Source
AI summary
There are provided a power supply device switching power input to a primary side to supply the power to a predetermined load connected to a secondary side electrically insulated from the primary side and a control circuit thereof. The control circuit generates a predetermined PWM signal to apply the PWM signal to a dimming switch connected to an end of the load and controls a switching frequency of the primary side, based on a control voltage generated according to a feedback signal according to the power supplied to the load and the PWM signal, and the control voltage maintains a constant difference between a minimum voltage level and a maximum voltage level regardless of a duty of the PWM signal.