LED Dimmer Lighting

  
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A dimmer for individual LED bulbs. LEDs (light emitting diodes) are very sensitive components - exceed their rated current or voltage and their lifespan can be slashed from 50, 000+ hours to an eventful microsecond. LEDs are current-driven * which means that the intensity of the light they generate depends on the amount of electric current flowing them. Typically current is controlled using a resistor in
LED Dimmer Lighting - schematic

series with the LED, or a current regulator circuit. Supplying more current to an LED increases its intensity, and reducing the current decreases its intensity. One way of dimming an LED is to use a variable resistor (potentiometer) to dynamically adjust the current getting to the LED and therefore increasing or decreasing its intensity. This works very well when just one LED bulb is involved. Unfortunately, all LEDs are not made equal - even those of nominally identical specifications from the same batch from the same manufacturer. Although this will not be apparent when strings of LEDs are being driven with the recommended forward current (e. g. 25mA for ultrabright LEDs), as the current is reduced some LEDs will turn off before others, and some will be dim when others are still quite bright etc. A far superior method of dimming LEDs is to use Pulse Width Modulation (PWM). With PWM strings of LED bulbs can all be driven with the recommended forward current, with the dimming achieved by turning the LEDs on and off at high frequency - so fast the human eye cannot see the strobing effect. The longer the on periods are relative to the off periods, the brighter the LEDs will appear to the observer. Duty Cycle is a percentage measure of the time that the LED is physically on. If, for example, the LED cycles ON for 9/1000 of a second, and then OFF for 1/1000 of a second, the duty cycle is 90%: 90% of the time it is ON, and 10%...



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