Open Loop LED Driver Adaptive Current Regulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Open loop LED driving circuits fail to maintain a constant average current due to line voltage variations, leading to luminance inconsistencies in LED modules, especially when capacitance is reduced or eliminated for cost reasons.
Innovation Solution
An adaptive open loop LED driving circuit that adjusts the turn-off period of the power switch in response to line voltage changes by using a resistive network to regulate the reference current, ensuring a constant average driving current through the resistors 407–409, and a capacitor to filter noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the capacitance of the capacitor is reduced or eliminated for cost reduction, then the cost of the circuit is reduced, but the average current varies severely with line voltage changes
Solution Approach 1:
The patent introduces a feedback mechanism by using a resistive network to sense the input voltage and adjust the turn-off period accordingly. The control unit monitors the voltage across the inductor and dynamically adjusts the switching timing to compensate for line voltage variations, ensuring stable average current even without a large capacitor.
Solution Approach 2:
The patent changes the timing parameters of the switching circuit by adjusting the turn-off period based on input voltage levels. The control unit varies the duty cycle and switching frequency dynamically, allowing the circuit to adapt to different line voltage conditions and maintain constant average current.
2Device complexity
If the turn-off period is fixed, then the circuit structure is simple, but the average current cannot remain constant when line voltage varies
Solution Approach 1:
The patent transforms the fixed turn-off period into a dynamic parameter that automatically adjusts with line voltage changes. The control unit continuously monitors voltage conditions and modifies the turn-off timing, enabling the circuit to maintain stable performance across varying input voltages without requiring complex external control circuits.
3Speed
If the NMOS transistor switching delay is present, then the circuit operates in real-time, but the peak current exceeds the threshold and average current becomes non-constant
Solution Approach 1:
The patent applies preliminary action by anticipating the switching delay effect and compensating for it in advance. The control unit calculates the required turn-off time based on the known delay characteristics and adjusts the switching timing proactively, ensuring that the current remains within acceptable limits despite the inherent delay.
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 circuit effectively maintains a constant average driving current irrespective of line voltage variations, enhancing the robustness and performance of open loop LED driving circuits by compensating for changes in line voltage through adaptive turn-off period adjustments.
Implementation Method 1
The inductor 104 is used for carrying the magnetic flux to provide a current ILED to drive the LED module 103
Implementation Method 2
The capacitor 101 is used to filter out the high frequency components from a voltage source VIN to generate a DC voltage
Implementation Method 3
The LED module 103 is the load of the open loop LED driving circuit
Data Source
AI summary
The present invention discloses an open loop LED driving circuit, having a turn-on period and a turn-off period, the circuit comprising: a power stage, used to store a magnetic energy supplied from a voltage source during the turn-on period and deliver the magnetic energy to a set of LEDs during the turn-off period; and a control unit, having a turn-off period control terminal coupled to the voltage source, and a channel of which a first terminal is coupled to the power stage and a second terminal is coupled to a reference ground, wherein the channel is switched on at a time according to the voltage of the voltage source to determine the turn-off period.