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Frequency response using SPICE

  1. May 14, 2007 #1


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    Gold Member

    I'm trying to plot the frequency response of a power supply I've designed. Here
    is the netlist (made using Spice OPUS):
    Code (Text):


    v1 4 5 dc 0 sin(0 34 60)

    D1 4 2 1N4007
    D2 0 5 1N4007
    D3 5 2 1N4007
    D4 0 4 1N4007

    c1 2 0 1000u
    c2 2 0 100n
    cout out 0 100n

    radj adj 0 5k
    r1 out adj 240

    x 2 adj out LM317

    .include parts.lib
    set units=degree
    destroy all

    tran 0.01ms 100ms
    plot v(4,5) v(out)  vs (time*1000)

    destroy all

    [b]ac dec 10 60Hz 7000Hz
    plot ac1.v(out) vs ac1.frequency[/b]

    The first plot, I'm doing a time domain analysis (this works fine). However, I am having some trouble with varying the frequency of the input. I have bold my attempt at this. But something is definitely wrong here. I get in excess of 6000v when I vary the frequency. When I designed the circuit I was aiming for about 29v (which is what the time domain plot shows).
    Can some please assist me in doing a frequency response analysis.

  2. jcsd
  3. May 21, 2007 #2


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    Gold Member

    Wow, no one here uses spice? Well it was a rather simple mistake. It turns out that to do a frequency response, I need to have the AC directive when defining the source (frequency domain).
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