Introduction to LTSPICE for Simulating Switches and Natural and Step Response of RC and RL Circuits

[@hieuphan5727]

Thank you! Very clear instruction and helpful.

[@electriccircuits7164]

Thank you for the feedback. Glad it helped your learning!

[@TohlaMende]

5:29 where did sir get the value for charging T=5ms. And why the switching time value = 50ms? How did you count final time and where did the value of 50 come from? What is the function for W expression you count there? And one more thing.. did the value for Trise and fall always 1us? Is step time=Trise and fall?

[@electriccircuits7164]

Thank you for the various questions. In this circuit, the 0.5uF capacitor charges through the 10kOhm resistor. Hence, the charging time constant is R*C= 5ms. Five time constants is 25ms. Thus, the capacitor will fully charge after 25ms. Therefore, we can set the switching time to anytime after 25 ms. In this simulation, the switching time is set to 50ms. The charging and discharging time constants are in ms. Thus, we can set the simulator step size as 1us. The time rise and time fall are set to the smallest value of 1us, which is the same value as the simulator step size. The energy stored in a capacitor is 0.5 C v(t)^2, which is a well know equation derived in textbooks.

[@bharatbohara3538]

Very interesting and useful video. Thank you for making this tutorial.

[@electriccircuits7164]

Thank you for the feedback. This channel is dedicated toward making expert thinking in electrical and electronic engineering visible to viewers. Glad the video was useful for your learning!

[@asokanselvaraj5413]

Thank you sir, very useful to us

[@electriccircuits7164]

Glad it has helped your learning!

[@robertofrazon604]

Parabéns !!! excelente vídeo

[@electriccircuits7164]

Thank you for the positive feedback!

[@Realisation404]

Great video sir 😊

[@electriccircuits7164]

Glad you found it useful to your learning!

[@stanleytaylor6484]

Very useful videos. I am planning to watch all of them. I could not figure out how to start a simulation with a switch already on. The newest version of LTspice [Version (x64): 17.1.6] requires more directives. I had to specify .ic v(vc)=0 (voltage on the capacitor), and each switch separately, or the programs assumes it is a steady state and gives an error message. If the videos could be updated, it would help greatly.

[@controlsystemtoolboxinmatl765]

Hello sir please upload the video of standard dual slope ADC implementation in LTSPICE.

[@electriccircuits7164]

Thank you for the excellent suggestion! I will definitely look into this.

[@MsTarcisiocs]

Great!!!!!!

[@electriccircuits7164]

Glad you liked it!

[@steffinmathew2565]

Why is 1 kilo ohm resistor connected to gate pulse circuit? What will happen if i model it without that resistor?

[@electriccircuits7164]

Thank you for the question. The simulation will still work if you do not connect the 1k Ohm resistors connected to the outputs of the pulse voltage sources.We have those resistors as conventionally we always measure any desired output voltage ina circuit across a resistor.

[@muhdmustaqiim0240]

excuse me sir where did R 32k ohm go & why are there resistors in the switch in the pulse?

[@electriccircuits7164]

Hello, Thank you for carefully watching the video and spotting the typo. Yes I forgot to connect the 32K resistor. It is part of the circuit we ware wanting to simulate and should be connected after the switch. The pulse voltages that control the switch can be directly connected to the switch but sometimes this can create singularities in the solver. Hence, it is better to connect the resistors (R5 and R6 in the LTSpice schematic) for numerical stability.

[@muhdmustaqiim0240]

@@electriccircuits7164 sir i still can't understand the part sir insert Von,TRise,Tfall by the calculation sir made can sir make another video to explain this if sir free?😅

[@electriccircuits7164]

I am not sure I understand your question correctly. Can you please try to state your confusion more clearly. Thanks!

[@muhdmustaqiim0240]

i don't understand the pulse detail that you insert those value on lt spice based on the manual calculation of step time,final time n so on// are my statement clear sir?

[@electriccircuits7164]

Example 1 in the video is a natural response of RC circuit example. We need to allow the switch to remain at position 'a' (05:10) for a sufficiently long time to allow the capacitor to fully charge. This sufficiently long time is determined by considering the charging time constant. In this example, we can set the switching time as 25 ms (5 charging time constants) or any time greater than that. In the video, it is set as 50ms. Once switching occurs, we need to continue the simulation for at least another 5 time constants to allow the capacitor to fully discharge. The discharging time constant is 40ms. This calculation of the discharging time constant is explained in this video: See kzbin.info/www/bejne/gWK0XnSvarmVrdk at 5 mins 39 secs into the video. Hence, we can work out the switching time and total simulation time. Hope this explains things!

[@marksymes8734]

I followed what you have done in the video but the capcitor does no discharge. Switches change over but capacitor charges up but stays charged. Is there something I missed in your video?

[@electriccircuits7164]

If you are constructing the same circuit as in the video and following all the instructions in the video, then it should work properly. I am assuming the circuit has been wired up correctly. Apart from the switches, please also check the initial conditions have been set properly, i.e., the initial voltage across the capacitor. Also, are you setting the simulation time properly?

[@ashikreza9470]

how many software are there like pspice , Ltspice ?>??

[@electriccircuits7164]

LTSpice, PSpice, PySpice are the main freeware softwares for circuit simulation. See a list of freeware circuit simulators here: en.m.wikipedia.org/wiki/List_of_free_electronics_circuit_simulators Multisim is also quite popular but it is a paid software en.m.wikipedia.org/wiki/NI_Multisim

[@ashikreza9470]

@@electriccircuits7164 thanks Boss