LED Driver Circuit SCR Turn-Off Control
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Solution Overview
Problem
Conventional LED driving circuits with SCR circuits experience irregular re-conduction, leading to flickering and noise due to oscillations in input current, resulting in inconsistent power absorption and brightness variations in LED loads.
Innovation Solution
An LED driver circuit incorporating a silicon-controlled rectifier (SCR) and a rectifier bridge to generate a phase-loss half sine wave voltage signal, along with a threshold voltage control circuit and a power switch control mechanism that ensures the power switch turns off only when the AC voltage reaches zero, preventing irregular re-conduction and maintaining consistent input power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SCR trigger circuit charges the SCR to conduct when input current is below holding current, then the SCR can be turned off, but oscillation is generated on input current causing irregular re-conduction
Solution Approach 1:
A capacitor is introduced as an intermediary energy storage element between the SCR trigger circuit and the SCR. This capacitor absorbs the energy that would otherwise cause oscillation, acting as a mediator to decouple the trigger circuit from the SCR and eliminate harmful current oscillations while maintaining reliable turn-off functionality.
Solution Approach 2:
The capacitor is pre-charged during the conduction period to store energy that will be released during the turn-off period. This beforehand cushioning prevents sudden energy release that would cause oscillation, ensuring smooth current transition and eliminating irregular re-conduction while maintaining reliable SCR control.
2Reliability
If the SCR re-conducts irregularly multiple times, then the SCR can be turned off, but the LED driving circuit absorbs different power from input side causing LED flicker and noise
Solution Approach 1:
The capacitor serves as an intermediary that smooths the power delivery to the LED load by absorbing and releasing energy in a controlled manner. This prevents sudden power variations that would cause LED flicker and noise, while maintaining reliable SCR control for dimming functionality.
Solution Approach 2:
The capacitor ensures continuous and stable power delivery to the LED load by maintaining a relatively constant voltage across it during the SCR turn-off period. This continuous action prevents power fluctuations that would cause LED flicker, ensuring smooth and noise-free operation while maintaining reliable SCR control.
3Ease of operation
If the power switch turns off when input current reaches holding current, then dimming control is achieved, but SCR oscillation occurs causing irregular re-conduction
Solution Approach 1:
The capacitor acts as an intermediary that decouples the dimming control mechanism from the SCR conduction state. This allows precise dimming control through independent voltage regulation while the capacitor absorbs oscillation energy, preventing SCR re-conduction instability and maintaining reliable operation.
Solution Approach 2:
The capacitor is pre-charged during SCR conduction to store energy that prevents oscillation during turn-off. This beforehand cushioning allows the power switch to turn off at the optimal moment for dimming control without causing SCR oscillation or irregular re-conduction, achieving both precise control and stability.
Data Source
AI summary
Disclosed are light-emitting diode (LED) driver circuits, methods, and a switch mode power supply. In one embodiment, an LED driver can include: (i) a silicon-controlled rectifier (SCR) and a rectifier bridge configured to receive an AC voltage, and to generate a phase-loss half sine wave voltage signal; (ii) a threshold voltage control circuit configured to receive a threshold voltage and an input voltage signal that represents the phase-loss half sine wave voltage signal, and to determine whether to output the threshold voltage based on angle information of the input voltage signal; (iii) a first control circuit configured to compare the input voltage signal against the threshold voltage output by the threshold voltage control circuit, and to generate a first control signal; and (iv) a power switch controllable by the first control signal to be off until an absolute value of the AC voltage is reduced to zero.