Passive Second Order Low-pass Circuit.

Hi everyone.

I am working on an assignment about passive second order low-pass filters. The circuit is attached.

We are given the placements of the passive components (Inductor(L1), Resistor(R1) and Capacitor(C1)) without their values.

The only given specification is that the cut-off frequency is 78 kHz.

My questions are:

1.How to make the predicted low-pass filter Transfer function for this specific circuit?

2.Secondly how do I calculate or choose the component values for the filter? ... ( A suggestion given to me was to choose a Inductor value and a Capacitor value that is at my disposal ant to calculate the required Resistor value to build the circuit after calculations ).

The components must work out so that:

2.1) the phase angle between the output voltage and input voltage is -90 degrees at the cut-off frequency (78 kHz).

AND

2.2) that the ratio of the amplitudes of the Output Voltage to the amplitude of the Input Voltage is 0.7079 at the cut-off frequency.

PS: I have a 1mH Inductor at my disposal,( thats why it is the only value I entered on the circuit for now :) ) and the Capacitors at my disposal is 1uF, 10uF, 22uF, 100uF or 470uF ).

I can't wait to here from you!

by iammichelle
April 05, 2018

The circuit transfer response should be Xc/(Xc+Xr+Xl). Simply substitute for these and you will see how to calculate the circuit values.

by mikerogerswsm
April 05, 2018

No Answers

No answers yet. Contribute your answer below!


Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account


Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers


Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.


About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.