Introduction: This simple circuit provides an extensive as well as a quite easy approach to build up a fading led circuit ( i-e : to make a led on and off ) without having to go for coding and programming. This circuit requires a couple of simple passive components which will result in constant fade up and fade down of the led. Similar to the led fade out dimmer, multiple LEDs can be used in parallel with one resistor per node taking into consideration the maximum ratings of the transistor before connecting a number of LEDs.





Resistor 10 k & 3.3 k
transistor BC-547
capacitor 100 mF
IC 555 timer
Light emitting diode(LED) Of any bright color
Battery 9 volts

WORKING: The main working components of this circuit are transistor and a capacitor. Fading LEDS can be constructed when negative terminal is grounded with respect to some applied voltage. The charging and discharging of capacitor causes led to fade up and down. In beginning, capacitor starts to charge through R1 and the transistor amplifies the current entering into the capacitor. As capacitor and resistor are in parallel connection, this gives some voltage signal to the base of amplifier thus it start to conduct (i-e : when voltage across capacitor raises same happens to the base of transistor) this delivers 100 times this value to the LED through collector emitter pins as the voltage across capacitor continues to increase it flows from collector to the emitter since it is connected to the ground potential. By the continuous generation of pulses led starts glowing. Since the capacitor’s voltage is still increasing, voltage across led will also increase and so they fade in slowly. Contrary to this, during discharging of capacitor the LEDs will fade out slowly until they get turned off. The periodical ups and down can be achieved by adjusting the values of resistors.

APPLICATIONS: The fading led circuits could be implemented in flowing areas of work.

  • In commercial places, to fade out lights when there is no crowd.
  • Security systems such as alarm set ups.
  • Domestic purposes as in decoration.
  • As indicators for vehicles.

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