pwm lamp dimmer using ne555

Posted on Feb 7, 2014

A simple and efficient PWM lamp dimmer using timer IC NE555 is discussed in this article. Yesterdays linear regulator based dimmerscan only attain a maximum efficiency of 50% and are far inferior when compared to the PWM based dimmers which can hit well over90% efficiency. Since less amount of power is wasted as heat, the switching elements of PWM

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dimmers require a smaller heat sink andthis saves a lot of size and weight. In simple words, the most outstanding features of the PWM based lamp dimmers are high efficiencyand low physical size. The circuit diagram of a 12V PWM lamp dimmer is shown below. As you can see, NE555 timer IC which is wired as an astable multivibrator operating at 2. 8KHz forms the heart of this circuit. Resistors R1, R2, POT R3 and capacitor C1 are the timing components. Duty cycle of the IC`s output can be adjusted using the POT R3 higher the duty cycle means higher the lamp brightness and lower the duty cycle means lower the lamp brightness. Diode D1 by-passes the lower half of the POT R3 during the charging cycle of the astable multivibrator. This is done in order to keep the output frequency constant irrespective of the duty cycle. Transistors Q1 and Q2 forms a darlington driver stage for the 12V lamp. Resistor R4 limits the base current of transistor Q1. As I have said earlier, the variable duty cycle astable multivibrator based on NE555 forms the foundation of this circuit and a good knowledge on it is essential for designing projects like this. For the ease of explanation the timing side of the astable multivibrator is redrawn in the figure below. Upper and lower halves of the POT R3 are denoted as Rx and Ry respectively. Consider the output of the astable multivibrator to be high at the starting instant. Now the capacitor C1 charges...

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