Documentation sections

Switching Regulator Output Ripple Calculator

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

Slug switching-regulator-ripple. Calculate buck converter output voltage ripple, inductor current ripple, and ESR contribution for switching regulator design

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 switching-regulator-ripple
Name	Unit	Range	Default	Description
inputVoltagenumber	V	at least 0.1	12	Input Voltage
outputVoltagenumber	V	at least 0.1	5	Output Voltage
frequencynumber	kHz	at least 1	500	Switching Frequency
inductancenumber	μH	at least 0.01	10	Inductance
capacitancenumber	μF	at least 0.1	100	Output Capacitance
esrnumber	mΩ	at least 0.1	20	Equivalent series resistance of the output capacitor
outputCurrentnumber	A	0.01 … 100	2	The load current: it sets the inductor's peak, the switches' RMS currents and the losses, not the ripple.
inputVoltageMinnumber	V	at least 0	0	The lowest input the regulator must work from; 0 for the nominal.
inputVoltageMaxnumber	V	at least 0	0	The highest input the regulator must work from; 0 for the nominal. The ripple is largest there.
rdsOnHighnumber	mΩ	0.1 … 10000	12	The high-side FET's on-resistance at its operating temperature.
rdsOnLownumber	mΩ	0.1 … 10000	6	The low-side (synchronous) FET's on-resistance at its operating temperature.
tSwitchnumber	ns	0 … 10000	20	The high side's rise and fall times added: the switching loss is ½·V_in·I_out·(t_r + t_f)·f_sw.
qgnumber	nC	0 … 10000	23	Both FETs' gate charge at the drive voltage: the gate drive takes Q_g·V_g·f_sw.
vGatenumber	V	1 … 20	5	Gate Drive Voltage
tDeadnumber	ns	0 … 1000	20	The time both FETs are off at each edge, when the low side's body diode carries the current.
vBodynumber	V	0 … 2	0.7	Body Diode Forward Voltage
dcrnumber	mΩ	0 … 100000	20	The inductor's winding resistance.
coreLossnumber	mW	0 … 100000	50	From the inductor's datasheet at this ripple and frequency.

Outputs

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

Outputs of switching-regulator-ripple
Field	Unit	Description
dutyCycle	%	Duty Cycle
inductorRippleCurrent	A	Inductor Ripple Current
capacitorRipple	mV	Capacitor Ripple Voltage
inductorRipple	mV	ESR Ripple Voltage
peakToPeakRippleheadline	mV	Total Peak-to-Peak Ripple
dutyMin	%	At the maximum input voltage
dutyMax	%	At the minimum input voltage
inductorRippleWorst	A	Inductor Ripple Current, Worst Case
inductorRippleWorstVin	V	Input at the Worst Inductor Ripple
ilPeakWorst	A	The load plus half the ripple; the inductor's saturation current must be at least this
ilPeakWorstVin	V	Input at the Worst Peak
rippleWorstMV	mV	Total Ripple, Worst Case
rippleWorstVin	V	Input at the Worst Ripple
coutRmsA	A	ΔI_L/√12, the inductor ripple the capacitor carries
coutRmsVin	V	Input at the Worst Capacitor Current
q1RmsA	A	High-Side FET RMS Current, Worst Case
q1RmsVin	V	Input at the Worst High-Side Current
q2RmsA	A	Low-Side FET RMS Current, Worst Case
q2RmsVin	V	Input at the Worst Low-Side Current
vdsRating	V	The rating sold at or above 1.5 times the maximum input
coutVoltageRating	V	The rating sold at or above 1.5 times the output
lossDcr	W	Inductor DCR Loss
lossCore	W	Inductor Core Loss
lossHsConduction	W	High-Side Conduction Loss
lossLsConduction	W	Low-Side Conduction Loss
lossHsSwitching	W	High-Side Switching Loss
lossGateDrive	W	Gate Drive Loss
lossDeadTime	W	Dead-Time Loss
lossCapEsr	W	Output Capacitor ESR Loss
lossTotal	W	Total Loss
outputPower	W	Output Power
efficiency	%	At the nominal input and load, from the loss model

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": "switching-regulator-ripple",
    "inputs": {
      "inputVoltage": 12,
      "outputVoltage": 5,
      "frequency": 500,
      "inductance": 10,
      "capacitance": 100,
      "esr": 20,
      "outputCurrent": 2,
      "inputVoltageMin": 0,
      "inputVoltageMax": 0,
      "rdsOnHigh": 12,
      "rdsOnLow": 6,
      "tSwitch": 20,
      "qg": 23,
      "vGate": 5,
      "tDead": 20,
      "vBody": 0.7,
      "dcr": 20,
      "coreLoss": 50
    }
  }'

import rftools

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

result = client.calculate("switching-regulator-ripple", {
    "inputVoltage": 12,
    "outputVoltage": 5,
    "frequency": 500,
    "inductance": 10,
    "capacitance": 100,
    "esr": 20,
    "outputCurrent": 2,
    "inputVoltageMin": 0,
    "inputVoltageMax": 0,
    "rdsOnHigh": 12,
    "rdsOnLow": 6,
    "tSwitch": 20,
    "qg": 23,
    "vGate": 5,
    "tDead": 20,
    "vBody": 0.7,
    "dcr": 20,
    "coreLoss": 50,
})
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": "switching-regulator-ripple",
    "inputs": {
      "inputVoltage": 12,
      "outputVoltage": 5,
      "frequency": 500,
      "inductance": 10,
      "capacitance": 100,
      "esr": 20,
      "outputCurrent": 2,
      "inputVoltageMin": 0,
      "inputVoltageMax": 0,
      "rdsOnHigh": 12,
      "rdsOnLow": 6,
      "tSwitch": 20,
      "qg": 23,
      "vGate": 5,
      "tDead": 20,
      "vBody": 0.7,
      "dcr": 20,
      "coreLoss": 50
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "switching-regulator-ripple",
	  "inputs": {
	    "inputVoltage": 12,
	    "outputVoltage": 5,
	    "frequency": 500,
	    "inductance": 10,
	    "capacitance": 100,
	    "esr": 20,
	    "outputCurrent": 2,
	    "inputVoltageMin": 0,
	    "inputVoltageMax": 0,
	    "rdsOnHigh": 12,
	    "rdsOnLow": 6,
	    "tSwitch": 20,
	    "qg": 23,
	    "vGate": 5,
	    "tDead": 20,
	    "vBody": 0.7,
	    "dcr": 20,
	    "coreLoss": 50
	  }
	}`)
	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": "switching-regulator-ripple",
  "values": {
    "dutyCycle": 41.66666666666667,
    "inductorRippleCurrent": 0.5833333333333334,
    "capacitorRipple": 1.4583333333333337,
    "inductorRipple": 11.666666666666668,
    "peakToPeakRipple": 11.75745921626872,
    "dutyMin": 41.66666666666667,
    "dutyMax": 41.66666666666667,
    "inductorRippleWorst": 0.5833333333333334,
    "inductorRippleWorstVin": 12,
    "ilPeakWorst": 2.2916666666666665,
    "ilPeakWorstVin": 12,
    "rippleWorstMV": 11.75745921626872,
    "rippleWorstVin": 12,
    "coutRmsA": 0.16839382851364088,
    "coutRmsVin": 12,
    "q1RmsA": 1.2955623749105833,
    "q1RmsVin": 12,
    "q2RmsA": 1.5329300747906054,
    "q2RmsVin": 12,
    "vdsRating": 20,
    "coutVoltageRating": 10,
    "lossDcr": 0.08056712962962963,
    "lossCore": 0.05,
    "lossHsConduction": 0.02014178240740741,
    "lossLsConduction": 0.014099247685185185,
    "lossHsSwitching": 0.12000000000000001,
    "lossGateDrive": 0.0575,
    "lossDeadTime": 0.028000000000000004,
    "lossCapEsr": 0.0005671296296296298,
    "lossTotal": 0.3708752893518519,
    "outputPower": 10,
    "efficiency": 96.42387668345947
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:switching-regulator-ripple",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "inputVoltage": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "outputVoltage": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "frequency": {
          "min": 1,
          "max": null,
          "unit": "kHz"
        },
        "inductance": {
          "min": 0.01,
          "max": null,
          "unit": "μH"
        },
        "capacitance": {
          "min": 0.1,
          "max": null,
          "unit": "μF"
        },
        "esr": {
          "min": 0.1,
          "max": null,
          "unit": "mΩ"
        },
        "outputCurrent": {
          "min": 0.01,
          "max": 100,
          "unit": "A"
        },
        "inputVoltageMin": {
          "min": 0,
          "max": null,
          "unit": "V"
        },
        "inputVoltageMax": {
          "min": 0,
          "max": null,
          "unit": "V"
        },
        "rdsOnHigh": {
          "min": 0.1,
          "max": 10000,
          "unit": "mΩ"
        },
        "rdsOnLow": {
          "min": 0.1,
          "max": 10000,
          "unit": "mΩ"
        },
        "tSwitch": {
          "min": 0,
          "max": 10000,
          "unit": "ns"
        },
        "qg": {
          "min": 0,
          "max": 10000,
          "unit": "nC"
        },
        "vGate": {
          "min": 1,
          "max": 20,
          "unit": "V"
        },
        "tDead": {
          "min": 0,
          "max": 1000,
          "unit": "ns"
        },
        "vBody": {
          "min": 0,
          "max": 2,
          "unit": "V"
        },
        "dcr": {
          "min": 0,
          "max": 100000,
          "unit": "mΩ"
        },
        "coreLoss": {
          "min": 0,
          "max": 100000,
          "unit": "mW"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "inputVoltage": 12,
      "outputVoltage": 5,
      "frequency": 500,
      "inductance": 10,
      "capacitance": 100,
      "esr": 20,
      "outputCurrent": 2,
      "inputVoltageMin": 0,
      "inputVoltageMax": 0,
      "rdsOnHigh": 12,
      "rdsOnLow": 6,
      "tSwitch": 20,
      "qg": 23,
      "vGate": 5,
      "tDead": 20,
      "vBody": 0.7,
      "dcr": 20,
      "coreLoss": 50
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "inputVoltage"
      ],
      "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 pageSwitching Regulator Output Ripple Calculator, at these values