RC Circuit Simulation in Simulink Shows Incorrect Charging Time

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Xiaolong
Xiaolong 2025-10-11
编辑： Torsten 2025-10-11
Hello,
I am simulating a simple RC circuit in Simulink (MATLAB R2025b) to observe the capacitor charging time. The circuit consists of a 1V DC voltage source, a 1-ohm resistor, and a 1-µF capacitor.
According to theory, the time constant (τ = R*C) is 1 µs. This means the capacitor voltage should reach approximately 63% of the source voltage (about 0.63V) at t = 1 µs.
However, my simulation shows a significant delay. The capacitor voltage only begins to rise noticeably between 2 µs and 3 µs, and does not match the theoretical curve at all.
I have attached my model file for reference. Could you please help me understand why the simulation results do not align with the theoretical expectations? I suspect it might be related to my solver configuration.
Thank you for your help.

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回答（1 个）

Paul
Paul 2025-10-11
Ran in:
Hi Xiaolong,
Disclosure: I did not actually open your model.
If you know the fastest system dynamics are on the order of 1e-6,consider changing the Max Step Size in the solver from auto to 1e-7, at least to see if that gets things going in the correct direction.
load_system('untitled');
c = getActiveConfigSet('untitled');
get_param(c,'Solver')
ans = 'VariableStepAuto'
get_param(c,'MaxStep')
ans = 'auto'
You can change the the Max Step Size in the Solver Pane, which can be acessed as shown at Set Model Configuration Parameters for a Model.

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