I've the following circuit:


simulate this circuit – Schematic created using CircuitLab

And I've to find the time-constant of the voltage across the inductor.

I did the following:

The voltage across the inductor is given by:


To find the rime constant I solved:

$$\frac{1}{e}\cdot U_L(0)=U_L(t)\space\Longleftrightarrow\space t=\frac{1}{10500}$$

Question: is the answer right? And is there an easier way to the solution?

  • \$\begingroup\$ You can just calculate R2 + R1||R3. \$\endgroup\$
    – The Photon
    Commented Jan 21, 2019 at 21:14
  • \$\begingroup\$ But don't forget to include the inductor value in your time constant calculation. \$\endgroup\$
    – The Photon
    Commented Jan 21, 2019 at 21:15

1 Answer 1


It is correct.

The easier way is the Thevenin equivalent R which is (R1||R3) +R2 = 1050\$\Omega\$ then \$T=L/R= 1 \mathrm{mH}/1050 Ω \$


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