# Notch filter implementation in PLECS

**URL:** <https://forum.plexim.com/t/notch-filter-implementation-in-plecs/1704>\
**Category:** PLECS\
**Tags:** plecs\
**Created:** [January 18, 2025, 4:10am UTC](https://forum.plexim.com/t/notch-filter-implementation-in-plecs/1704 "2025-01-18T04:10:33Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![ptos](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@ptos](https://forum.plexim.com/u/ptos)\
**Post date:** [January 18, 2025, 4:10am UTC](https://forum.plexim.com/t/notch-filter-implementation-in-plecs/1704/1 "2025-01-18T04:10:33Z")

</div>

as i impement the notch filter in PLECS, seems it doesn’t work,

 ![image](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/5/54efe9ac9783e6b922c4ab2410a22266c0dc6ac3.png)

as input a PFC output voltage with 100Hz RIPPLE, but output the exact same output without filter effective.

 ![image](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/a/aa7d760693f9bedc705fb686d98dd89bdaed5ba9.png)

PLECS version: 4.8.6

---

<div class="post-metadata">

**Author:** ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)\
**Post date:** [January 20, 2025, 7:52pm UTC](https://forum.plexim.com/t/notch-filter-implementation-in-plecs/1704/2 "2025-01-20T19:52:09Z")

</div>

The notch frequency for the transfer function you entered is not 100 Hz but rather 100 Radians/sec (15.915 Hz). Given the Q factor your filter, the 100 Hz component is unaltered.

 ![notch](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/7/70eb4b547c3db78043bdd5a9165eed843fe3a640.png)

---

<div class="post-metadata">

**Author:** ![ptos](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@ptos](https://forum.plexim.com/u/ptos)\
**Post date:** [January 21, 2025, 1:38am UTC](https://forum.plexim.com/t/notch-filter-implementation-in-plecs/1704/3 "2025-01-21T01:38:46Z")

</div>

Dear bryan

it’s really nice to catch the feedback,  
actually, i want to know what’s the problem with the implementation, i’ve tried use continuous transfer function but not worked, i had made the model by mathcad, and it output the same graphic as you shared;  
if i can download any function model(continuous/ discrete) to evaluate;

thanks a lot;

petros Li  
+86 18576628096

---

<div class="post-metadata">

**Author:** ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)\
**Post date:** [January 21, 2025, 4:54pm UTC](https://forum.plexim.com/t/notch-filter-implementation-in-plecs/1704/4 "2025-01-21T16:54:08Z")

</div>

The horizontal axis in my graphic is Radians/sec. I suspect that is the case in your Mathcad script as well. In that case you can simply make sure you consistently use Radians/sec or Hz and apply 2π factors where needed. As for the basic design of a notch filter, this is explained in many textbooks and references.

I’m aware of two demo models that use notch filters the “Three-Level Boost PFC Converter” PLECS demo model and the “On-board Charger” TI C2000 TSP model. The On-board charger model is more sophisticated in that it also determines the discrete transfer function coefficients using Tustin with prewarp at the notch frequency.