When controlling a group of LEDs for lighting applications, the relationship between LED brightness and electrical power is a key technical indicator that determines the quality of visible light. In low-power applications, it may not be possible to illuminate the entire set of LEDs to achieve large brightness due to the limited current source. In order to achieve excellent brightness when using a low power supply, the power consumption of each LED must be effectively managed. This requires a power management technique that provides power to only one of a set of LEDs at a given time. The time interval is also managed to achieve the desired illumination intensity without visually detecting that each set of LEDs is alternately lit. Figure 1: Using a monostable flip-flop circuit to control the LED lighting interval UGR LED Downlight,LED Recessed Downlight,UGR Adjust LED Downlight,UGR LED Commercial Downlight SHENZHEN KEHEI LIGHTING TECHNOLOGY CO.LTD , https://www.keheiled.com
To determine the number of LEDs that illuminate during a given time interval, the available power and luminous intensity of the application must be determined. The relationship between luminous intensity and forward current characteristics in the LED data sheet must be carefully examined to select the LED that meets the desired brightness level. Once the number of LEDs required to achieve the desired brightness level is determined, the ratio of the total current to the available current for the LED can be calculated by determining the number of LEDs that can be powered during a given time interval:
The number of LEDs = total current required by the LED / total available power supply
In addition, the frequency at which a group of LEDs are turned on/off must be adjusted. The lighting time should be sufficient to cause all of the LEDs to illuminate, and the extinguishing time is limited by the time it takes for the set of LEDs to begin to become significantly darker. The off time limits the number of other LED groups that can be controlled in the application when a group of LEDs is off. Therefore, the extinction time limits the number of LED groups that can be managed by the time interval.
The low-cost implementation of this technology requires a clock source, a digital monoflop for controlling several sets of LEDs, and an OR gate that can detect the start condition with a simple On/Off switch. Figure 1 shows a block diagram of the D monoflop configuration used to control four groups of LEDs. .jpg)
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The monostable flip-flop is initially in a state of no change and requires a start pulse. The duration of the start pulse must be at least one clock cycle so that the first flip-flop can detect the pulse on the rising edge of the clock. In addition, the start signal must be a transient signal. It cannot exceed one clock cycle, otherwise the first two trigger outputs will be set at the same time; and because the source current is limited, the lighting application will not work properly. Therefore, with this configuration, a set of LEDs is fully illuminated on the rising edge of each clock. But in the eyes of the human eye, it is like all LEDs are lit at the same time.
The limitation of this implementation is that it is monotonous and the design lacks flexibility. It has only one lighted or extinguished state. For some applications, such as LCD backlighting, this circuit can be used. However, if dimming or mode generation is required, microcontroller-based (MCU)-based circuits offer great flexibility and have minimal impact on the overall cost of the solution. And the circuit is easier to build and has fewer components. The MCU controls each set of LEDs while simultaneously detecting user inputs for dimming control and mode selection. 