BJT Total Dissipation

P = VCE × IC + VBE × IB

Quick answer

This calculator solves P = VCE × IC + VBE × IB for P. With VCE 12 V, IC 2 A, VBE 26.4 V, IB 20 mA, the result is 24.53 W.

Calculator

Result
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Formula

P = VCE × IC + VBE × IB

Description

The total power dissipated in a bipolar junction transistor is the sum of collector-emitter power and base-emitter power. In most practical circuits, the collector-emitter term (VCE × IC) dominates because IC is much larger than IB. When the BJT is used as a switch in saturation, VCE_sat is typically 0.1-0.3V, making dissipation quite low. In the active (linear) region, VCE can be significant and the BJT acts as a variable resistor, dissipating potentially large amounts of power. The base-emitter term is usually small but should not be ignored in precision calculations.

Variables

  • P — Total power dissipation (W)
  • VCE — Collector-emitter voltage (V)
  • IC — Collector current (A)
  • VBE — Base-emitter voltage (V)
  • IB — Base current (A)

Practical Notes

In saturation, VCE_sat increases with collector current and decreases with higher base overdrive. A common rule of thumb is to set IB = IC / (β × 0.5) to ensure deep saturation. Safe operating area (SOA) curves in the datasheet define the maximum allowable combinations of VCE and IC.

Symbols and units

Symbol Meaning Default unit Accepted units
Vce VCE V pV, nV, µV, mV, V, kV
Ic IC A pA, nA, µA, mA, A, kA
Vbe VBE V pV, nV, µV, mV, V, kV
Ib IB mA pA, nA, µA, mA, A, kA

Step by step

  1. 1. What you know: VCE 12 V, IC 2 A, VBE 26.4 V, IB 20 mA
  2. 2. The relation: P = VCE × IC + VBE × IB
  3. 3. Substitute: Vce = 12 V, Ic = 2 A, Vbe = 26.4 V, Ib = 20 mA
  4. 4. Result: P = 24.53 W

Related quantities from the same inputs

  • P = V × I = 24 W

Worked examples

Minimum range

Given: VCE 0.33 V, IC 2 mA, VBE 0.726 V, IB 100 µA

Result: P = 7.33 × 10⁻⁴ W

Low range

Given: VCE 3.3 V, IC 20 mA, VBE 7.26 V, IB 1 mA

Result: P = 0.07326 W

Typical

Given: VCE 12 V, IC 2 A, VBE 26.4 V, IB 20 mA

Result: P = 24.53 W

High range

Given: VCE 0.23 kV, IC 100 A, VBE 0.506 kV, IB 0.5 A

Result: P = 23250 W

Maximum range

Given: VCE 2.3 kV, IC 1 kA, VBE 5.06 kV, IB 5 A

Result: P = 2.33 × 10⁶ W

How P changes with VCE

VCE (input) P (result)
1.2 V 2.928 W
3 V 6.528 W
6 V 12.53 W
9 V 18.53 W
12 V 24.53 W
18 V 36.53 W
24 V 48.53 W
48 V 96.53 W
84 V 168.5 W
120 V 240.5 W

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Frequently asked questions

How do you calculate BJT Total Dissipation?

Use P = VCE × IC + VBE × IB. With VCE 12 V, IC 2 A, VBE 26.4 V, IB 20 mA, P works out to 24.53 W.

What is the formula for BJT Total Dissipation?

The formula is P = VCE × IC + VBE × IB. The total power dissipated in a bipolar junction transistor is the sum of collector-emitter power and base-emitter power.

Related Concepts

All Semiconductors formulas →
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