# How to analyze first-order transient circuits using Simulink?

I have been trying to design a first-order circuit with a capacitor but, I could't achieve to initaliaze the steady-state condition. I mean I was not able to close the switch at t = 0. Since, I am using a dc voltage source, at t = 0 capacitor voltage must be equal steady-state value. My question is how can I achieve that?

Could you tell me which block should I use ın Simulink?

This is the circuit that ı had designed

• Simulink is overkill . You can choose any initial voltage in Falstad. Jan 9, 2022 at 22:11
• tinyurl.com/y24qex7h Jan 9, 2022 at 22:19

The problem with these questions is t=0 does not imply that at t=0 the power is also applied, they imply t=-∞ the power supplies are "turned on" and a steady-state condition is achieved.

This is crucial when you consider how simulations work since they typically by default initialize with current and voltage all at zero and thus if a switch is commanded at t=0 the result mentioned in the question will occur, no matter the simulation engine used.

Different simulation packages solve this in different way and one of them is performing a DC bias point "pre simulation". Simulink is no different but how you solve this is up to you and upto "convinience"

Without doing anything this is the results

OPTION #1 redefine t=0 to be t=TBD where TBD is determined via separate simulation, ~ 3.3seconds.

In this instance you can see at t=5 the step is enabled

OPTION #2 If you determine the DC bias point (separate simulation), you can set the initial voltage on the capacitors and have a step time of t=0

• I am so appriciated for your answer. But can I ask you which value you have assigned for the series resistor parameter in the capacitor ? Jan 10, 2022 at 12:56