PWM using 555.

A simple oscilator with PWM that can be used to control speed of motors or light intensity. (4/29/2006)


Pulse width modulation (PWM) is a technique to control analog circuits with a digital output. PWM is used in many applications, Specially to control light intensity and speed on motors.


A PWM circuit makes a square wave with a variable width. The pulse width in this circuit can be varied from 5% to 95%. Used in a dimmer, this circuit controls the light intensity according the pulse width. On speed controller, the power of the motor depends the width from 5% (low power/speed) to 95% (full power/speed)


The main disadvantage of this circuit, as all PWM circuits, is the possibility of generating radio frequency interference (RFI). It can be reduced changing the capacitor.


A PMW using a 555 oscillator.


Parts needed:
* 1 1k Resistor
* 1 1mF Capacitor (Tantalium capacitors works great)
* 2 4148 Diodes
* 1 100k Variable resistor
* 1 IC 555 oscillator.


Germanium diodes can be used to increase the range of the PMW up to 1% to 99%.



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