IC 555 Pulse Position Modulator Circuit is similar to the circuit of Astable multivibrator circuit. But here we use control voltage pin-5 to modulate the output frequency of AMV circuit.
Connection Details
In this application, IC 555 works as astable multivibrator circuit. The timing capacitor C charges through resistors R1 and R2 and discharges through R2 only. A triangular wave i.e. modulating signal voltage Vm is connected to pin-5. Due to this the output signal of the IC is modulated. Suppose, the battery voltage is 12V. So the 1/3 voltage level for internal trigger comparator is 4V and 2/3 voltage level for threshold comparator is 8V.
Working
Initially suppose Vm = 0, so the 1/3 voltage level is 4V and 2/3 voltage level is 8V. But when Vm increases, the 1/3 and 2/3 voltage levels of the IC proportionally increase. Thus when Vm = 0, the output frequency of the circuit will be –
In this way, when Vm increases the output frequency increases proportionally. And when Vm decreases the output frequency decreases proportionally. Thus, the position of output pulses changes as the amplitude of modulating signal changes. Hence, this circuit is called pulse position modulator circuit.
You can change the output frequency value as required in your experiment by using the IC 555 Online Calculator.
Pure Output Waveform
This is the pure output waveform without applying the triangular wave at control voltage pin-5.
PWM Waveform
This is the output waveform when we apply triangular wave at control voltage pin-5 of the IC 555. It clearly shows that when amplitude of triangular wave increases, the output frequency proportionally increases i.e. we get compressions and when amplitude of triangular wave decreases, the output frequency decreases i.e. we rare fractions.
Practical Circuit on Breadboard
Animated Video
We would love to receive your feedback regarding this article. If you have any queries, suggestions, etc. please drop your comments below.
Vidyasagar Academy 