Pulse Width Modulator Using 555 IC

A very simple pulse modulator circuit can be built using 555 IC. In 555 chip, a special modulator input is available at pin 5. Here is the schematic diagram of circuit:

This pulse modulator circuit need an external clock signal to work. You can build an astable multivibrator using the same 555 IC or using any other type of  square wave oscillator to provide the clock signal. The clok signal must be fed to the trigger input (pin 2) of this pulse width modulator circuit. The modulation input should be fed to pin 5, and you’ll get the pulse-width-modulated output at pin 3.  [Circuit’s schematic diagram source: National Semiconductor Application Notes]