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BJT Voltage-Divider Bias Calculator — result sheet
Estimate the base, collector, and emitter currents and the Q-point of an NPN transistor using a voltage-divider bias model.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: VTH=VCC·R2/(R1+R2); RTH=R1∥R2; IB=max(0,(VTH−VBE)/(RTH+(β+1)RE)); IC=βIB; IE=(β+1)IB; VCE=VCC−ICRC−IERE.
A resistor divider can establish a base-bias voltage while the emitter resistor provides feedback in a simple NPN common-emitter stage. This page first replaces the divider with its Thevenin voltage and resistance, then estimates base current and reconstructs the collector, emitter, and collector-emitter voltages. It reports when the forward-active equations run out of supply headroom instead of silently calling an impossible result a valid Q-point.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Supply voltage VCC — V; minimum 1.0E-6; maximum 1000000
- Upper divider resistor R1 — Ω; minimum 1.0E-6; maximum 1000000000000
- Lower divider resistor R2 — Ω; minimum 1.0E-6; maximum 1000000000000
- Collector resistor RC — Ω; minimum 1.0E-6; maximum 1000000000000
- Emitter resistor RE — Ω; minimum 1.0E-6; maximum 1000000000000
- Current gain β — β; minimum 1.0E-6; maximum 1000000
- Base-to-emitter voltage VBE — V; minimum 0; maximum 10
Worked example
| Input | Value |
|---|---|
| Supply voltage VCC | 12 |
| Upper divider resistor R1 | 47000 |
| Lower divider resistor R2 | 10000 |
| Collector resistor RC | 1000 |
| Emitter resistor RE | 1000 |
| Current gain β | 100 |
| Base-to-emitter voltage VBE | 0.7 |
The Thevenin divider is about 2.105 V and 8,246 Ω; the estimate gives IB ≈ 12.86 µA, IC ≈ 1.286 mA, and VCE ≈ 9.414 V in the forward-active region.
Assumptions and limits
- The transistor is NPN and the base-emitter drop is a visitor-supplied constant VBE.
- β is treated as a constant DC current gain and the divider is represented by its Thevenin equivalent.
- The active-region current equations are used for the estimate; a negative or very small VCE is reported as a saturation warning rather than solved with a separate saturation model.
- Resistor values are positive and share ohms; supply and voltage values use volts.
- Frequency response, transistor variation, temperature, Early effect, leakage, saturation voltage, power dissipation, and hardware safety are outside the model.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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