LTspice urgent help

Discussion in 'General Electronics Chat' started by rizwan.bashir, Aug 22, 2013.

  1. rizwan.bashir

    Thread Starter New Member

    Aug 14, 2013

    I am trying to merge a sinewave and a DC voltage so that the sinewave overrides on the DC voltage. The DC voltage is actually a pulse consisting of +24V and -12V pulses. The sincewave has a frequency of 500Khz and an amplitude of 10V pk.
    When I try to do it in LTspice, I cannot see any sinewave merged with the pulse train. I am attaching my circuit and when I try to see the waveform on the right end of the capacitor, I see only the pulse train and no sinewave.
    I tried to remove the capacitor and inductor and tried to see the waveform at the junction, but still I only see the pulse train. The sinewave is being generated, it is just that after the resistor, I cannot have anything about sinewave.

    Why is that happening in LTspice and how do I fix it?
  2. tindel

    Well-Known Member

    Sep 16, 2012
    Right Click on the voltage supply, click the 'Advanced' button, click on the 'Sine' radio button. Set your DC offset to your desired voltage.

    Another way is to put the two power supplies in series. One DC, and one AC sine wave.
  3. rizwan.bashir

    Thread Starter New Member

    Aug 14, 2013
    Thank you for your reply. Actually you are right. But what I actually am doing is a bit different. Please see the attached file now. If I see the waveform on the right side of R2, I have an attenuated sine wave, but on the left side of R1, I only have the pulse train. I am actually trying to see how the sinewave is transmitted to the other end (the pulse train). What should I do? It is actually a simulation of power line communication circuitry. In which you have to deliver power and communicate through the same line.
  4. crutschow


    Mar 14, 2008
    If you put two voltage sources in parallel they will short each other since their ideal impedance is zero. You need to put them in series if you want both a pulse and a sinewave at the same time.