Fly-back Power Supply with Linear Current Regulator for LED Drive
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Solution Overview
Problem
Existing switched power supplies for driving light-emitting diodes (LEDs) face challenges in providing stable and ripple-free current, which is crucial for maintaining optimal light intensity and operational parameters, especially under varying ambient conditions, and current solutions are costly and complex for smaller power supplies.
Innovation Solution
A method combining a switched fly-back power supply with a linear current regulator on the secondary side, using the difference between secondary and load voltages as a control signal to regulate the output current, thereby reducing ripple and power loss, and enabling cost-effective control of the light intensity of LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a switched fly-back power supply is used to drive LEDs, then the power supply can deliver feed voltage exactly as large as the load instantaneously requires, but ripple currents arise in the output filter condensors that cause visible blinking of the LEDs
Solution Approach 1:
A linear current regulator is introduced as an intermediary component between the fly-back power supply and the LED load. This regulator acts as a mediator that smooths the ripple current from the switched power supply while maintaining the adaptive feed voltage capability, thereby eliminating visible LED blinking without sacrificing voltage adaptability
Solution Approach 2:
The patent combines two different power supply topologies - the switched fly-back converter and the linear current regulator - into a single hybrid system. The fly-back stage provides adaptive voltage delivery while the linear regulator stage filters ripple current, achieving both adaptability and smooth current delivery for LED operation
2Object-affected harmful factors
If the output filter is complicatedly dimensioned to reduce ripple, then the ripple effect is reduced, but the component dimensioning requires more space and increases cost, particularly for smaller power supplies
Solution Approach 1:
The filtering function is segmented into two stages: the first stage uses the inherent output filter of the fly-back converter, and the second stage introduces a simple linear current regulator with minimal filtering components. This segmentation allows ripple reduction without requiring a single complex, space-consuming filter design
Solution Approach 2:
The patent replaces the expensive, space-consuming complex filter design with a simple, inexpensive linear current regulator circuit. This regulator uses minimal components (transistor, resistors, capacitors) to achieve the same ripple reduction effect, making it particularly suitable for smaller, cost-sensitive power supply applications
3Loss of energy
If a constant current is used to drive LEDs, then operating economy and low power loss are achieved, but the current must be high enough to drive the load and achieve required light intensity
Solution Approach 1:
The system uses dynamic current regulation where the linear current regulator continuously adjusts the LED drive current based on real-time load requirements and ambient conditions. This dynamic adjustment ensures the minimum necessary current is always supplied, achieving low power loss while maintaining required light intensity without excessive current
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 approach provides a cost-effective and efficient means to control and monitor output current, significantly reducing ripple and power loss, making the system suitable for driving LEDs with stable and low-ripple current delivery, particularly effective for low output voltages and small non-linear loads.
Implementation Method 1
using the difference between secondary and load voltages as a control signal to regulate the output current
Data Source
Figure 1A
Figure 1B~2B
Figure 2A
AI summary
The invention concerns a method for monitoring and controlling the output current from an electronic drive system of the type that has a switched power supply (1) of fly-back type. The invention concerns also an electronic drive system and the use of such a drive system. According to the method, a switched power supply (1) of fly-back type is used for the driving of a load, for example a non-linear load of light-emitting diodes, whereby the output current (lout) from the power supply is controlled by means of pulse-width modulation through the ratio between the lengths of the ON and OFF phases of a switch in the primary circuit. The output current of the drive system is controlled and monitored through: - the selection of a switched power supply (1) of single-stage type and with a power factor correlation of PF, - the arrangement of a linear current regulator (15) at the output (UCout) of the switched power supply (1), - the regulation of the current (IL) through the load that is connected to the output (Uout) of the linear current regulator (15) by means of the linear current regulator (15), - the measurement and use of the fall in voltage (M1-M2) across the linear current regulator (15) in the formation of a first control signal (S1) that is led through a feedback loop (18, 19; 18, 19, 20) to a primary side of the power supply (1), - the use of the control signal (S1 ) for the control of the output voltage (Uout) of the power supply (1) through regulation of the duty cycle of the switch (SW), - the conversion of an AC voltage (Uin) to a rectified DC voltage (U1 ) that is fed in its raw, unfiltered or solely half-wave rectified form to the input terminals of the power supply (1).