Documentation sections

BJT Transistor Bias Point Calculator

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

Slug bjt-bias-point. Calculate BJT voltage divider bias Q-point including collector current, base voltage, VCE, power dissipation, and operating region

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 bjt-bias-point
Name	Unit	Range	Default	Description
vccnumber	V	at least 0.1	12	Supply Voltage (VCC)
r1number	kΩ	at least 0.001	10	R1 (upper bias resistor)
r2number	kΩ	at least 0.001	4.7	R2 (lower bias resistor)
rcnumber	kΩ	at least 0.001	2.2	Collector Resistor
renumber	Ω	at least 0	470	Emitter Resistor
betanumber	none	at least 1	100	Current Gain (β / hFE)
vbenumber	V	0.1 … 0.9	0.7	Base-Emitter Voltage

Outputs

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

Outputs of bjt-bias-point
Field	Unit	Description
vb	V	Base Voltage
ve	V	Emitter Voltage
vc	V	Collector Voltage
icheadline	mA	Collector Current
ib	μA	Base Current
vce	V	Collector-Emitter Voltage
powerDissipation	mW	Power Dissipation
operatingRegion	none	Operating Region (1=Active, 0=Sat)

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": "bjt-bias-point",
    "inputs": {
      "vcc": 12,
      "r1": 10,
      "r2": 4.7,
      "rc": 2.2,
      "re": 470,
      "beta": 100,
      "vbe": 0.7
    }
  }'

import rftools

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

result = client.calculate("bjt-bias-point", {
    "vcc": 12,
    "r1": 10,
    "r2": 4.7,
    "rc": 2.2,
    "re": 470,
    "beta": 100,
    "vbe": 0.7,
})
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": "bjt-bias-point",
    "inputs": {
      "vcc": 12,
      "r1": 10,
      "r2": 4.7,
      "rc": 2.2,
      "re": 470,
      "beta": 100,
      "vbe": 0.7
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "bjt-bias-point",
	  "inputs": {
	    "vcc": 12,
	    "r1": 10,
	    "r2": 4.7,
	    "rc": 2.2,
	    "re": 470,
	    "beta": 100,
	    "vbe": 0.7
	  }
	}`)
	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": "bjt-bias-point",
  "values": {
    "vb": 3.6369426751592355,
    "ve": 2.9369426751592353,
    "vc": -1.7473912454262077,
    "ic": 6.248814202466458,
    "ib": 62.488142024664576,
    "vce": -4.684333920585443,
    "powerDissipation": 0,
    "operatingRegion": 0
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:bjt-bias-point",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "vcc": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "r1": {
          "min": 0.001,
          "max": null,
          "unit": "kΩ"
        },
        "r2": {
          "min": 0.001,
          "max": null,
          "unit": "kΩ"
        },
        "rc": {
          "min": 0.001,
          "max": null,
          "unit": "kΩ"
        },
        "re": {
          "min": 0,
          "max": null,
          "unit": "Ω"
        },
        "beta": {
          "min": 1,
          "max": null,
          "unit": ""
        },
        "vbe": {
          "min": 0.1,
          "max": 0.9,
          "unit": "V"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "vcc": 12,
      "r1": 10,
      "r2": 4.7,
      "rc": 2.2,
      "re": 470,
      "beta": 100,
      "vbe": 0.7
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "vcc"
      ],
      "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 pageBJT Transistor Bias Point Calculator, at these values