Author – Arpita Kashyap


LED is a light emitting diode or a semiconductor device that emits visible light when an electric current is passes through it. LED bulb is an assembly of components packaged to fit into a common light socket. In most of the cases, light emitting from semiconductor device is monochromatic that means occurring at a single wavelength. LED can be used in flashing indicators, led dimmers, traffic signals, led bulbs, and so on. They have longer life time, low energy power consumption, small in size, faster switching.

Dimmers are the devices used to increase or decrease the brightness of a light. By changing the voltage applied to the lamp, it is possible to increase or decrease the intensity of the light output. Generally the term dimmer is used to those, who intended to control the output light  intensity for LED, CFL etc.

Modern dimmers are made up of semiconductors instead of variable resistors because of their higher efficiency.  A variable resistor would dissipate power as heat and acts as a voltage divider. Since semiJconductor dimmers switch quickly between low resistance “on” state and a high resistance “off” state, they dissipate very little power compared with the controlled load.

Block diagram of LED Light Dimmer

Components requirement

  1. Capacitor – 100μF (C1)
  2. Resistor – 1k (R1,R2)
  3. LED Green (D1)
  4. NPN Transistor  – 547 (Q1)
  5. 555 Timer IC

Circuit Diagram of LED Light Dimmer

In below diagram we use, 555 timer in astable mode that means pin number 2 and pin number 6 are short together while pin 4 and pin 8 are connected together to VCC of 12V. The 12V battery is connected to VCC for operating voltage of 555 timer. Pin number 1 is grounded. One end of capacitor is connected to pin number 2 and other end is connected to ground. Capacitor is connected for varying the voltage to generate the PWM in various duty cycle by its charging and discharging phenomena. Pin number 2 and pin number 6 have upper and lower comparator respectively in internally of 555 timer IC.The upper comparator has the value 2/3 VCC of the VCC and lower comparator has 1/3 of the VCC. Pin 3 is connected to resistor of 1k and further resistor is connected to NPN  transistor. Now another resistor of 1k is connected with the LED and further LED is grounded.

Circuit Diagram of LED Light Dimmer

The astable multivibrator is high at starting then capacitor C1 is started to charge. When capacitor reaches to voltage of 2/3 its VCC, then upper comparator makes the astable multivibrator to goes low. Then the voltage in the capacitor starts to discharge. When it reaches the voltage of 1/3 VCC, then lower comparator flips and make the astable multivibrator to go high. Here diode D1 plays the key role, diode will allow the voltage when the capacitor is discharging and it will not allow reverse current when the multivibrator is at high or capacitor is charging. The high and low of the multivibrator , generates pulse.

There are two main method for dimming a component LED

  1. Analog

In this dimming, the forward current to the LED is varied. Its electronics linearly reduces the current so as to dim the LED. The efficiency of the LED is increased when run at a lower current (dimming reduces operating temperatures inside the light source). In most of the LED they have a nearly linear forward current to visible lumen output relationship. While a simpler circuit can often achieve this effect, there are other concerns such as what to do with excess current when it is not consumed by the LED.

  1.   PWM (Pulse Width Modulation)

It is a method of controlling how often a high frequency wave is high versus low. The frequency is high enough that a phenomenon of Persistence of Vision occurs in which the human eye cannot perceive the rapid on and off the light and the result appears to be dimming. Because the current applied to the led is constant when the PWM signal is in its on stage, the current consumption is constant and this results more reliable color output even when dimmed.