SCR Dimming Circuit with Feedback Control for LED Flicker
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Solution Overview
Problem
Conventional SCR dimming circuits cause flicker in LED lamps due to fluctuations in bus voltage and repeated turning on of the SCR element, affecting the linearity of dimming.
Innovation Solution
An SCR dimming circuit with a dimming control circuit that includes phase angle detection, output current feedback, input current control, and maximum operation time detection, which generates a driving signal to manage the power converter's operation based on bus voltage, output current, and input current sampling signals, ensuring the SCR element is not repeatedly turned on, thereby stabilizing the bus voltage and eliminating flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the SCR element is used to control lamp luminance by turning on/off or dimming, then the lamp brightness can be adjusted, but the SCR element repeatedly turns on during half sine wave cycles causing bus voltage fluctuations and LED flicker
Solution Approach 1:
The patent implements feedback control by detecting the AC input current and comparing it with a predetermined value (holding current). When the detected current exceeds the holding current, the control circuit generates an invalid signal to prevent SCR turn-on, and when it falls below the holding current, the control circuit allows SCR turn-on. This feedback mechanism stabilizes bus voltage by preventing SCR operation during conditions that would cause voltage fluctuations, thereby eliminating LED flicker while maintaining dimming functionality.
2Adaptability or versatility
If the SCR element is turned on frequently to achieve dimming control, then the dimming range is improved, but the linearity of dimming deteriorates due to repeated turning on cycles
Solution Approach 1:
The patent changes the control parameter from simple on/off switching to current-threshold-based control. By monitoring the AC input current and comparing it with the holding current threshold, the system dynamically adjusts SCR operation based on actual current conditions rather than fixed timing. This parameter change ensures smooth, linear dimming across the full range by preventing erratic SCR turn-on events that would disrupt dimming linearity.
3Ease of operation
If the AC input current decreases below the holding current of the SCR element, then the SCR element turns off, but it is then turned on again after charging for predetermined time causing repeated cycling
Solution Approach 1:
The patent introduces an intermediary control circuit between the AC power supply and the SCR element. This control circuit includes current detection means that continuously monitors the AC input current and a control signal generation means that processes the detected current signal. The intermediary circuit generates appropriate control signals (valid or invalid) based on the comparison between detected current and holding current, thereby managing SCR turn-on/off timing without adding complex external control mechanisms.
Data Source
AI summary
A silicon-controlled rectifier (SCR) dimming circuit and a dimming control method are disclosed. The SCR dimming circuit includes a SCR element, a rectifier circuit, a filter circuit, a power converter, and a dimming control circuit. The dimmer control circuit includes a phase angle detection circuit, an output current feedback control circuit, an input current control circuit, a maximum operation time detection circuit, and a logic operator. An input current sampling signal fluctuates near a predetermined value after the SCR element is turned off by turning on and off the power converter, so that the input AC current is less than a holding current of the SCR element. The present SCR dimming circuit and the present dimming control method can avoid repeatedly turning on the SCR element in cycles of an operating frequency. Thus, the linearity of dimming is improved and the flicker of an LED lamp is eliminated.