Sardar Vallabhbhai Patel Institute
of Technology
TOPIC:PWM LED DIMMER/BRIGHTNESS
CONTROL BY 555 TIMER
MADE BY:SHAH DHRUTI(130410109097)
PUNJABI DIVYA (130410109088)
PRAJAPATI YOGESHWARI (130410109086)
SEWANI KAJOL (130410109094)
Contents:
•
•
•
•
Principle
Components
Working
Applications
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?
...
• 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.
Components Required for LED
Dimmer Controller
•
•
•
•
•
Resistors (4.7kΩ)
Potentiometer (10kΩ)
Capacitor (100nF or 0.1µF)
555 timer IC
Diode
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.
...
• 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).
...
• 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.
•
…
• 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)
...
• Pulse with can be varied by changing the
charging and discharging time, this is possible
by adjusting the potentiometer. Thus we get
PWM signal…!
Applications
• Used in malls
• In DJ lights
• By setting frequency we can set the brightness
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.