Calculator Inputs
Use optional fields for deeper stage analysis and export-ready results.
Example Data Table
Use these sample values to test the calculator quickly.
| Device | Config | Ib (mA) | Ic (mA) | Ie (mA) | Vin (V) | Vout (V) | Pin (mW) | Pout (mW) | Rc (Ω) | RL (Ω) | Re (Ω) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2N3904 | CE | 0.04 | 6.80 | 6.84 | 0.02 | -3.10 | 0.15 | 8.01 | 1000 | 2200 | 47 |
| BC547 | CE | 0.02 | 3.20 | 3.22 | 0.015 | -1.90 | 0.08 | 3.45 | 1500 | 3300 | 56 |
| Darlington | Stage | 0.01 | 8.50 | 8.51 | 0.03 | -4.60 | 0.12 | 12.50 | 820 | 1800 | 22 |
Formula Used
The calculator combines direct gain ratios with small-signal transistor relationships.
Primary current gains
β = Ic / Ib gives common-emitter current gain.
α = Ic / Ie gives common-base current gain.
γ = Ie / Ib links emitter current to base current.
Voltage and power gain
Av = Vout / Vin measures voltage amplification.
Ap = Pout / Pin measures power amplification.
Gain(dB) uses 20 log10(|ratio|) for voltage or current, and 10 log10(ratio) for power.
Thermal voltage and transconductance
Vt = kT / q and is about 25.85 mV near room temperature.
gm = Ic / Vt estimates BJT small-signal transconductance using collector current in amperes.
Estimated stage gain
Rload,eff = Rc || RL is the parallel load resistance.
Av(stage) ≈ -gm × (Rc || RL) / (1 + gm × Re) estimates common-emitter stage voltage gain with emitter degeneration.
How to Use This Calculator
Follow these steps for reliable transistor gain analysis.
- Enter the transistor name, type, and configuration for reference.
- Provide Ib and Ic to calculate β.
- Provide Ic and Ie to calculate α.
- Provide Vin and Vout to calculate voltage gain.
- Provide Pin and Pout to calculate power gain.
- Add temperature to improve the transconductance estimate.
- Add Rc, RL, and Re for stage-gain estimation.
- Press Calculate Gain to show results, graph, and export buttons above the form.
FAQs
Plain HTML questions and answers for quick reference.
1. What does transistor gain mean?
Transistor gain describes how much a device amplifies current, voltage, or power. In BJTs, β is the most common current-gain measure, while α is used in common-base analysis.
2. Why is β usually larger than α?
β compares collector current with base current, and base current is much smaller than emitter current. α compares collector current with emitter current, so α usually stays just below one.
3. Can I use this tool for common-emitter circuits?
Yes. The calculator is especially useful for common-emitter work because it computes β, voltage gain, decibel gain, and an estimated small-signal stage gain using resistor values.
4. What if I do not know emitter current?
If base and collector currents are entered, the calculator estimates emitter current with Ie = Ic + Ib. This is a standard current relationship for BJTs.
5. Why is my voltage gain negative?
A negative voltage gain usually indicates phase inversion. Common-emitter amplifiers often invert the output signal, so a negative value is normal and not automatically an error.
6. How is transconductance estimated here?
The calculator estimates BJT transconductance with gm = Ic / Vt. Temperature affects Vt, so changing temperature slightly changes the small-signal gain estimate.
7. Are the decibel formulas different for power and voltage?
Yes. Voltage and current ratios use 20 log10, while power ratios use 10 log10. That difference matters when converting linear gain into decibels.
8. Why should I export CSV or PDF results?
Exports help document design checks, compare devices, and share engineering calculations with teammates, clients, or reports without retyping every output value manually.