Documentation sections

MOSFET Power Dissipation Calculator

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

Slug mosfet-power-dissipation. Calculate MOSFET conduction loss, switching loss, total power dissipation, junction temperature, and efficiency for power electronics 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 mosfet-power-dissipation
Name	Unit	Range	Default	Description
drainCurrentnumber	A	at least 0.001	5	RMS drain current through the MOSFET
rdsonnumber	mΩ	at least 0.1	10	Drain-source on-resistance from datasheet
vdsnumber	V	at least 0.1	12	Voltage across MOSFET during off state (bus voltage)
frequencynumber	kHz	at least 0.1	100	Switching frequency of the converter
riseTimenumber	ns	at least 0.1	20	Current rise time during turn-on transition
fallTimenumber	ns	at least 0.1	20	Current fall time during turn-off transition
rthJAnumber	°C/W	1 … 300	40	Junction-to-ambient thermal resistance. TO-220 no heatsink: ~60, with heatsink: ~10-20, SOT-23: ~150
tAmbientnumber	°C	−40 … 85	25	Operating ambient temperature
drainCurrentMinnumber	A	at least 0	0	The lowest RMS drain current in service; 0 for the nominal.
drainCurrentMaxnumber	A	at least 0	0	The highest RMS drain current in service; 0 for the nominal. The junction temperature is taken at the highest current and ambient.
tAmbientMinnumber	°C	−40 … 150	0	The coldest ambient in service, which may be below 0 °C; 0 for the nominal.
tAmbientMaxnumber	°C	−40 … 150	0	The hottest ambient in service; 0 for the nominal.
rdsonTempconumber	%/°C	0 … 2	0	R_DS(on) rises as R_DS(on)·(1 + α·(T_j − 25 °C)), typically by 0.35 to 0.5 %/°C (M. Keagy, Electronic Design, 2002). With α above 0, R_DS(on) is the 25 °C value and the junction temperature is solved with it; 0 takes R_DS(on) as given at every temperature.
qgnumber	nC	0 … 10000	20	At the gate drive voltage: the driver delivers Q_g·V_g·f_sw, which it dissipates, so it is not in the junction temperature.
vGatenumber	V	1 … 20	10	Gate Drive Voltage
cossnumber	pF	0 … 100000	0	Its energy ½·C_oss·V_DS² is lost in the channel at each hard turn-on (IR AN-1070); give the datasheet's energy-related C_o(er) where it has one. 0 leaves it out.

Outputs

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

Outputs of mosfet-power-dissipation
Field	Unit	Description
conductionLoss	mW	Conduction Loss
switchingLoss	mW	Switching Loss
totalLossheadline	mW	Total Power Loss
junctionTemp	°C	Junction Temperature
efficiency	%	MOSFET Efficiency (1 − P_loss/P_in)
junctionTempWorst	°C	At the corner of the current and ambient ranges where it is highest
junctionTempWorstCurrent	A	Drain Current at the Hottest Junction
junctionTempWorstAmbient	°C	Ambient at the Hottest Junction
junctionTempCoolest	°C	At the lowest current and ambient: with the worst case, the junction's swing over the envelope
totalLossWorst	mW	Total Power Loss, Worst Case
totalLossWorstCurrent	A	Drain Current at the Worst Loss
efficiencyWorst	%	Efficiency with Gate Drive, Worst Case
efficiencyWorstCurrent	A	Drain Current at the Worst Efficiency
drainCurrentWorst	A	The MOSFET's continuous drain current rating must be at least this, at its operating temperature
vdsRating	V	The rating sold at or above 1.5 times the drain-source voltage
lossConduction	W	I_D²·R_DS(on) at the junction temperature
lossSwitching	W	½·V_DS·I_D·(t_r + t_f)·f_sw
lossOutputCap	W	½·C_oss·V_DS²·f_sw, lost at each hard turn-on
lossGateDrive	W	Q_g·V_g·f_sw, dissipated in the gate driver
lossTotal	W	The MOSFET's loss and its gate drive
outputPower	W	V_DS·I_D, the power the MOSFET efficiency is taken against, less the losses
efficiencyLossModel	%	1 − (MOSFET loss + gate drive)/(V_DS·I_D), at the nominal current and ambient

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": "mosfet-power-dissipation",
    "inputs": {
      "drainCurrent": 5,
      "rdson": 10,
      "vds": 12,
      "frequency": 100,
      "riseTime": 20,
      "fallTime": 20,
      "rthJA": 40,
      "tAmbient": 25,
      "drainCurrentMin": 0,
      "drainCurrentMax": 0,
      "tAmbientMin": 0,
      "tAmbientMax": 0,
      "rdsonTempco": 0,
      "qg": 20,
      "vGate": 10,
      "coss": 0
    }
  }'

import rftools

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

result = client.calculate("mosfet-power-dissipation", {
    "drainCurrent": 5,
    "rdson": 10,
    "vds": 12,
    "frequency": 100,
    "riseTime": 20,
    "fallTime": 20,
    "rthJA": 40,
    "tAmbient": 25,
    "drainCurrentMin": 0,
    "drainCurrentMax": 0,
    "tAmbientMin": 0,
    "tAmbientMax": 0,
    "rdsonTempco": 0,
    "qg": 20,
    "vGate": 10,
    "coss": 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": "mosfet-power-dissipation",
    "inputs": {
      "drainCurrent": 5,
      "rdson": 10,
      "vds": 12,
      "frequency": 100,
      "riseTime": 20,
      "fallTime": 20,
      "rthJA": 40,
      "tAmbient": 25,
      "drainCurrentMin": 0,
      "drainCurrentMax": 0,
      "tAmbientMin": 0,
      "tAmbientMax": 0,
      "rdsonTempco": 0,
      "qg": 20,
      "vGate": 10,
      "coss": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "mosfet-power-dissipation",
	  "inputs": {
	    "drainCurrent": 5,
	    "rdson": 10,
	    "vds": 12,
	    "frequency": 100,
	    "riseTime": 20,
	    "fallTime": 20,
	    "rthJA": 40,
	    "tAmbient": 25,
	    "drainCurrentMin": 0,
	    "drainCurrentMax": 0,
	    "tAmbientMin": 0,
	    "tAmbientMax": 0,
	    "rdsonTempco": 0,
	    "qg": 20,
	    "vGate": 10,
	    "coss": 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": "mosfet-power-dissipation",
  "values": {
    "conductionLoss": 250,
    "switchingLoss": 120,
    "totalLoss": 370,
    "junctionTemp": 39.8,
    "efficiency": 99.38333333333334,
    "junctionTempWorst": 39.8,
    "junctionTempWorstCurrent": 5,
    "junctionTempWorstAmbient": 25,
    "junctionTempCoolest": 39.8,
    "totalLossWorst": 370,
    "totalLossWorstCurrent": 5,
    "efficiencyWorst": 99.35,
    "efficiencyWorstCurrent": 5,
    "drainCurrentWorst": 5,
    "vdsRating": 20,
    "lossConduction": 0.25,
    "lossSwitching": 0.12,
    "lossOutputCap": 0,
    "lossGateDrive": 0.02,
    "lossTotal": 0.39,
    "outputPower": 59.61,
    "efficiencyLossModel": 99.35
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:mosfet-power-dissipation",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "International Rectifier AN-1070 (J. Cerezo), P_CONDUCTION, P_SWITCHING and P_GATE; Infineon, D. Graovac, M. Pürschel and A. Kiep, MOSFET Power Losses Calculation Using the Data-Sheet Parameters (2006); M. Keagy, Calculate Dissipation for MOSFETs in High-Power Supplies (Electronic Design, 2002)",
    "assumptions": [
      {
        "code": "one-current-for-both-losses",
        "text": "The drain current is the RMS current for the conduction loss and the current switched at each edge for the switching loss, which holds for a current that is flat while the MOSFET conducts at a duty cycle near 100 %."
      },
      {
        "code": "linear-rdson-temperature",
        "text": "With a temperature coefficient α, R_DS(on) is the 25 °C value and rises as R_DS(on)·(1 + α·(T_j − 25 °C)) (M. Keagy, Electronic Design, 2002); the junction temperature is the steady state of T_j = T_A + R_θJA·P(T_j), absent where α·R_θJA·R_DS(on)·I_D² ≥ 1 (thermal runaway)."
      },
      {
        "code": "gate-drive-in-the-driver",
        "text": "The gate drive Q_g·V_g·f_sw is dissipated in the driver and the gate resistance, so it is in the loss model's total and efficiency and not in the junction temperature; the output capacitance's ½·C_oss·V_DS²·f_sw is lost in the channel and is in both (IR AN-1070)."
      },
      {
        "code": "waveforms-at-half-duty",
        "text": "The calculator takes no duty cycle, so the waveforms are drawn at 50 % duty, with each switching edge split equally between the current and the voltage transition, the linear approximation whose energy is ½·V_DS·I_D·t (Infineon, Graovac et al., 2006)."
      }
    ],
    "validRange": {
      "status": "inside",
      "bounds": {
        "drainCurrent": {
          "min": 0.001,
          "max": null,
          "unit": "A"
        },
        "rdson": {
          "min": 0.1,
          "max": null,
          "unit": "mΩ"
        },
        "vds": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "frequency": {
          "min": 0.1,
          "max": null,
          "unit": "kHz"
        },
        "riseTime": {
          "min": 0.1,
          "max": null,
          "unit": "ns"
        },
        "fallTime": {
          "min": 0.1,
          "max": null,
          "unit": "ns"
        },
        "rthJA": {
          "min": 1,
          "max": 300,
          "unit": "°C/W"
        },
        "tAmbient": {
          "min": -40,
          "max": 85,
          "unit": "°C"
        },
        "drainCurrentMin": {
          "min": 0,
          "max": null,
          "unit": "A"
        },
        "drainCurrentMax": {
          "min": 0,
          "max": null,
          "unit": "A"
        },
        "tAmbientMin": {
          "min": -40,
          "max": 150,
          "unit": "°C"
        },
        "tAmbientMax": {
          "min": -40,
          "max": 150,
          "unit": "°C"
        },
        "rdsonTempco": {
          "min": 0,
          "max": 2,
          "unit": "%/°C"
        },
        "qg": {
          "min": 0,
          "max": 10000,
          "unit": "nC"
        },
        "vGate": {
          "min": 1,
          "max": 20,
          "unit": "V"
        },
        "coss": {
          "min": 0,
          "max": 100000,
          "unit": "pF"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "drainCurrent": 5,
      "rdson": 10,
      "vds": 12,
      "frequency": 100,
      "riseTime": 20,
      "fallTime": 20,
      "rthJA": 40,
      "tAmbient": 25,
      "drainCurrentMin": 0,
      "drainCurrentMax": 0,
      "tAmbientMin": 0,
      "tAmbientMax": 0,
      "rdsonTempco": 0,
      "qg": 20,
      "vGate": 10,
      "coss": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "drainCurrent"
      ],
      "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/"
}

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Same inputs on the calculator pageMOSFET Power Dissipation Calculator, at these values