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# LTSpice

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#### t.man

##### New Member
hi,

is it possible to simulate (plot) max. power transfered to load by changing R load in LTSpice?

What do you mean?

It's easy to plot the power dissipated by a load, just set the trace expression to (V(nXXXX)-V(nXXXX))*I(Load)

V(nXXXX) are the nodes at either side of the load.

What do you mean?

It's easy to plot the power dissipated by a load, just set the trace expression to (V(nXXXX)-V(nXXXX))*I(Load)

V(nXXXX) are the nodes at either side of the load.

what i mean is that; i want to vary the value of R load and plot the power dissipated to load resistance. hence be able to see the maximum power dissipated to the load.

ok?

Last edited:
No, I don't know how to do that.

hi t,
Is this what you are asking.?

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• AAAimage01.gif
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• ParaTherm1a.asc
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hi t,
Another example.

Click RUN, place the cursor on the load resistor so that the meter icon is displayed and press the ALT key to show a thermometer icon.

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• AAAimage02.gif
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• ParaTherm1b.asc
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Last edited:
what i mean is that; i want to vary the value of R load and plot the power dissipated to load resistance. hence be able to see the maximum power dissipated to the load.

ok?

Do you mean the peak power or the average power?
The peak power can be had the way Hero told you about.

If you need the average power you would integrate i(t)*e(t)
over all time, which is the same as using an RC filter on i(t)*e(t)
where the time constant is large compared to the change in
the amplitude of the waveform.

hi t,
Is this what you are asking.?

hi eric,
ok, i'm using PSpice now.
actually what i was thinking is this (if i'm right, ok?);

looking at the circuit below, RL (or R9) will dissipate maximum power when equals to thervenin resistance( which equals 230.8k if i'm correct).

i was expecting power to increase till R9= 230.8k then decrease afterwards.
am i right? if yes, why isn't the case here looking at the plot.

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• cct.JPG
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• plot.JPG
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hi eric,
ok, i'm using PSpice now.
actually what i was thinking is this (if i'm right, ok?);

looking at the circuit below, RL (or R9) will dissipate maximum power when equals to thervenin resistance( which equals 230.8k if i'm correct).

i was expecting power to increase till R9= 230.8k then decrease afterwards.
am i right? if yes, why isn't the case here looking at the plot.

hi t,

hi t,

hi, eric

i think i've got it.
i've created RL as a global parameter.
isn't what i should expect?

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• try.JPG
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hi, eric

i think i've got it.
i've created RL as a global parameter.
isn't what i should expect?

hi t,
Please post your asc file, in that way I can compare your results without having to build the sim.

I would suggest that you look in spice tools menu and change the plot background colour to white , also make the plot lines wide/thick.

hi t,
Please post your asc file, in that way I can compare your results without having to build the sim.

I would suggest that you look in spice tools menu and change the plot background colour to white , also make the plot lines wide/thick.

hi,
i can't identify asc file in my project files. where can i find it?

Eric, he's using Pspice now. I suspect that's why he can't find the .ASC file.

Eric, he's using Pspice now. I suspect that's why he can't find the .ASC file.

Thanks Ron for confirming that.

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