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Transistor Biasing Calculator

Work out transistor biasing instantly with clear inputs, formula shown and shareable results.

About Transistor Biasing Calculator

In an emitter-degenerated stage the emitter voltage is the base voltage minus 0.7 V, so emitter current is that divided by Re. Collector-emitter voltage is the supply minus the drop across both resistors, and the small-signal gain is -Rc/(Re + re) where re is the intrinsic emitter resistance 26 mV/Ie.

Formula

BJT bias point

Ve = Vb - 0.7; Ie = Ve / Re; Vce = Vcc - Ie(Rc + Re); Av = -Rc / (Re + 26mV/Ie)

Worked example

With the default values below, Transistor Biasing Calculator returns Collector current of 3.83. Change any input above and every figure here is recalculated in your browser.

Inputs used

Supply voltage
12 V
Collector resistor
2,200 Ω
Emitter resistor
470 Ω
Base voltage
2.5 V

Results

Collector current
3.83 mA
Collector-emitter voltage
1.7745 V
Quiescent dissipation
6.80 mW
Small-signal voltage gain
-4.61 x

Step by step

  1. 1Values used
  2. 2BJT bias point
  3. 3Collector current= 3.83 mA
  4. 4Collector-emitter voltage= 1.7745 V
  5. 5Quiescent dissipation= 6.80 mW
  6. 6Small-signal voltage gain= -4.61 x

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why include an emitter resistor?

It stabilises the operating point against beta and temperature variation by providing negative feedback, at the cost of gain.

Where should Vce sit?

Around half the supply for maximum symmetrical swing, and at least a volt or two above saturation across the whole temperature range.

Related Calculators

Transistor Biasing Calculator – Calculate Collector current