1. TOPIC:PWM LED DIMMER/BRIGHTNESS CONTROL BY 555 TIMER
Sardar Vallabhbhai Patel Institute of Technology
TOPIC:PWM LED DIMMER/BRIGHTNESS CONTROL BY 555 TIMER
MADE BY:SHAH DHRUTI( )
PUNJABI DIVYA ( )
PRAJAPATI YOGESHWARI ( )
SEWANI KAJOL ( )

2. Contents:
Principle
Components
Working
Applications

3. PRINCIPLE
How to change the brightness of a LED? Whether led lights are dimmable? Is it possible to adjust the brightness of LEDs? LED is basically a diode, when the forward voltage exceeds 0.7 volt, it starts to glow, and if the forward voltage is less than 0.7 volt, it will be in the OFF state. What happens if we are providing a high voltage to the LED so as to increase the brightness?

4. ...
Will it be a practical solution? No, it will lead to the burning of LED. So what we can do to adjust the brightness of LEDs? Here Circuits Gallery comes with a simple LED brightness control circuit using (Pulse Width Modulation) PWM method. It is also called PWM LED dimmer circuit diagram. By changing the pulse width of square wave, it is possible to control the brightness of LED. We have already discussed about the PWM signal generation before. HereNE555 timer IC is used to produce PWM signals.

5. Components Required for LED Dimmer Controller
Resistors (4.7kΩ)
Potentiometer (10kΩ)
Capacitor (100nF or 0.1µF)
555 timer IC
Diode

6. Working of PWM LED Light Dimmer Circuit
We have already discussed about Pulse Width Modulation(PWM) Op-Amps and 555 ICs are widely used for generating PWM signals.
Our new circuit is based on 555 timer IC. You can use this circuit as a dimmer switch for LED lights. This PWM concept is also applicable for lamp dimmer switches too. But here we are explaining about 555 led dimmer.

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At the instant of powering ON the circuit, output will be 5V, because the voltage at the 2nd pin (trigger pin) is less than 1/3 Vcc.
At the very next moment, the output voltage will reach the capacitor via the 10kΩ potentiometer and diode D2 so that the capacitor starts charging with a time constant RdR1C (where Rd is the forward resistance of Diode D2).

9. ...
When the capacitor voltage exceeds 2/3 Vcc, the 555 timer gets reset. Then the output will be 0V.
At this moment the capacitor discharges via the diode D1 and potentiometer R1 to the output pin since it is in ground potential.

11. …
When the capacitor voltage goes below 1/3 Vcc, the output of 555 IC again rises to 5V. This process continues.
Here the charging and discharging path is entirely different since it is isolated by diodes D1 and D2 (refer above images). If the potentiometer midpoint is at 50% (middle), we will able to get 50% duty cycle (square waves of equal pulse width)

13. ...
Pulse with can be varied by changing the charging and discharging time, this is possible by adjusting the potentiometer. Thus we get PWM signal…!

14. Applications Used in malls In DJ lights
By setting frequency we can set the brightness

15. Summary
PWM is a better approach for dimming LED instead of linear current.
PWM dimming prevents unwanted color shift on LED while maintaining the required light itensity.
The implementation of PWM dimming becomes very simple and do not require any extensive ckt design or extra ckt components.