PWM LED Lighting Circuit With Parallel Dummy Load for Flicker Control
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Solution Overview
Problem
The existing LED lighting systems in the film-television industry face issues with discontinuous load causing flicker, limited brightness adjustment range, and inaccurate color stability due to the discontinuous load and response time of switching tubes, which are not suitable for professional camera photography requirements.
Innovation Solution
An LED lighting circuit with a non-light-emitting load element connected in parallel to the LED light-emitting element, controlled by a control circuit to manage current phases, and a temporal dimmer control circuit using partially overlapped PWM waveforms to ensure continuous load during transitions, allowing for accurate brightness and color adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM temporal dimming is used to control LED lamp bead strings, then brightness adjustment is achieved, but discontinuous load causes flicker and abnormal circuit operation
Solution Approach 1:
A dummy load is introduced as an intermediary component connected in parallel with the LED lamp bead string. This dummy load acts as a mediator to receive and dissipate the inductance energy that would otherwise cause abnormal discharge and circuit operation instability. The dummy load ensures continuous current path during PWM switching, eliminating flicker and abnormal brightness while maintaining brightness adjustment functionality.
2Device complexity
If a single constant-current source is used, then circuit complexity is reduced, but brightness adjustment range is limited
Solution Approach 1:
The patent employs dynamic control of the dummy load's switching timing relative to the PWM signal. By adjusting the dummy load's on/off moments, the system can adapt to different brightness levels and current conditions. This dynamic adjustment allows a single constant-current source to achieve wide brightness adjustment range by optimizing the dummy load's operation at different working states, eliminating the need for multiple constant-current sources.
3Ease of operation
If switching tubes are used for PWM control, then brightness control is achieved, but response time causes discontinuous load and flicker
Solution Approach 1:
The dummy load serves as a mediator that compensates for the switching response time of the switching tubes. During the transition period when the LED string is being switched, the dummy load maintains continuous current flow, ensuring that the load appears continuous to the constant-current source. This eliminates the discontinuous load effect caused by switching tube response time, preventing flicker and maintaining color stability.
4Reliability
If inductance energy is not properly discharged, then circuit operation is stable, but abnormal discharge causes flicker and brightness abnormalities
Solution Approach 1:
The patent converts the harmful inductance energy that would cause abnormal discharge into a beneficial effect. By connecting the dummy load in parallel with the LED string and controlling its switching timing, the inductance energy is deliberately directed to the dummy load where it can be safely dissipated as heat. This transforms the potentially harmful energy discharge into a controlled process that stabilizes the circuit operation and eliminates flicker.
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
The solution provides stable and accurate color with a wide range of brightness adjustment, meeting the requirements of professional photography by ensuring continuous load and reducing heat loss and flicker.
Implementation Method 1
the non-light-emitting load element is controlled to be connected in the current rising or falling phase of the constant-current source to consume circuit energy in a non-constant-current phase
Implementation Method 2
LED light-emitting element
Data Source
AI summary
Disclosed is an LED lighting circuit based on PWM, including a power source, a control circuit and an LED light-emitting element, and further including a non-light-emitting load element. The non-light-emitting load element is connected in parallel to the LED light-emitting element, the power source is connected to a constant-current source, the constant-current source supplies power to the LED light-emitting element and the non-light-emitting load element, and when the constant-current source is in a current rising or falling phase, the control circuit controls an LED light-emitting element loop to be disconnected, and controls a non-light-emitting load element loop to be connected; and when the current of the constant-current source is in a steady state, the control circuit controls the non-light-emitting load element loop to be disconnected, and controls the LED light-emitting element loop to be connected.