Hello all,
I am new to this forum and I hope this is the right environment to ask my question.
I am running a transient analysis and I want the value of a resistor to be varied through out the simulation.
What I need in more detail is:
R=30Ohm until t=200nsec
Then R is decreased linearly to 0hm between t=200nsec and t=250nsec
And finally R starts increasing exponentially to 30 Ohms from t=250nsec until t=500nsec.
Is this possible to do? I am familiar with parametric sweep but I am not able to come up with a way to use for this example.
Many thanks in advance.
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V1 2 1 EXP 0 30 250n 50n 500n 1m
V2 1 0 PULSE 30 0 200n 50n 50n 1m 1
E1 node1 node2 VALUE={I(E1)*V(2,0)}
Thank you for your reply! Using the two voltage sources in series seems like something that could work.
To provide a bit of a background to what I am trying to do: The resistor I am referring to is the collector resistance of a BJT and is connected in series with the BJT. The BJT is turned on by a transient current and this variation of Rc is meant to reproduce the thermal effects in the transistor.
I am not sure though, about how I should use and connect the E source you mention. Since we are interested in the current why not using a current dependant source?
So, coming back to my last reply, I figured out how the E source should be used.
I can't however find a way to use I(E) as the gain of the E source and I always get an error. is there any example available on how to set the current of the source itself as the gain?
I don't understand how you are setting up your circuit. Is the BJT an NPN or PNP? How is R(t) tied into it? Would you post a netlist or an image of your circuit if using Capture to create your schematic.
This my original circuit, where Q5 is the NPN BJT I am simulating and Rtc is the collector resistor, which has a constant value. I5 is a transient pulse which turns on the BJT and F5 is simulating a regenerative feedback mechanism.
Based on your suggestion, I modified the circuit accordingly:
I used the two voltage sources and connected them to the E source, which is placed at the position of the resistor. I can't figure out though how to change the gain of the EE source and set it equal to I(E).
Change the EXPR property from V(%IN+, %IN-) to V(%IN+, %IN-)*(I(E^@REFDES)).
Connect IN+ to VR and IN- to 0.
Connect OUT+ to F5 and OUT- to Q5.
That worked great! Thank you very much, I really appreciate the help.
Setup a Voltage source and choose the output you want. Label the output net VResistance.
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