Documentation sections

Differential Mode EMI Filter

POSThttps://rftools.io/api/py/v1/calculate

Slug differential-mode-filter. Design a differential mode LC EMI filter. Calculate corner frequency, attenuation, and impedance for SMPS output noise suppression.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of differential-mode-filter
Name	Unit	Range	Default	Description
inductancenumber	μH	0.001 … 100000	47	Differential Mode Inductance
capacitancenumber	μF	0.001 … 1000	0.47	Differential Mode Capacitance
frequencynumber	kHz	at least 0.001	150	Problem Frequency
eSeriesnumber	none	0 … 96	0	Rounds every part to the nearest value in the series; the response and the export are the rounded design's.One of: 0 Ideal values · 12 E12 (10%) · 24 E24 (5%) · 48 E48 (2%) · 96 E96 (1%)

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of differential-mode-filter
Field	Unit	Description
cornerFreq	kHz	Corner Frequency
attenuationheadline	dB	Attenuation at f
characteristicImpedance	Ω	Characteristic Impedance

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "differential-mode-filter",
    "inputs": {
      "inductance": 47,
      "capacitance": 0.47,
      "frequency": 150,
      "eSeries": 0
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("differential-mode-filter", {"inductance": 47, "capacitance": 0.47, "frequency": 150, "eSeries": 0})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "differential-mode-filter",
    "inputs": {
      "inductance": 47,
      "capacitance": 0.47,
      "frequency": 150,
      "eSeries": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "differential-mode-filter",
	  "inputs": {
	    "inductance": 47,
	    "capacitance": 0.47,
	    "frequency": 150,
	    "eSeries": 0
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "differential-mode-filter",
  "values": {
    "cornerFreq": 33.86275384933944,
    "attenuation": -25.85475941398055,
    "characteristicImpedance": 10
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:differential-mode-filter",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "inductance": {
          "min": 0.001,
          "max": 100000,
          "unit": "μH"
        },
        "capacitance": {
          "min": 0.001,
          "max": 1000,
          "unit": "μF"
        },
        "frequency": {
          "min": 0.001,
          "max": null,
          "unit": "kHz"
        },
        "eSeries": {
          "min": 0,
          "max": 96,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "inductance": 47,
      "capacitance": 0.47,
      "frequency": 150,
      "eSeries": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "inductance"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageDifferential Mode EMI Filter, at these values