BJT Vbe vs Temperature

Vbe(T) = Vbe_ref − 0.002 × ΔT

Quick answer

This calculator solves Vbe(T) = Vbe_ref − 0.002 × ΔT for Vbe at Temp. With Vbe Reference 1.32 V, Temperature Change 50 °C, the result is 1.22 kV.

Calculator

Result
—

Formula

Vbe(T) = Vbe_ref − 0.002 × ΔT

Description

The base-emitter voltage of a BJT decreases approximately 2 mV per degree Celsius increase in temperature. This well-known temperature coefficient is remarkably consistent across different transistor types and is exploited in bandgap voltage references and temperature sensors. At room temperature, Vbe is typically 0.6-0.7V for silicon transistors, dropping to about 0.5V at 100°C above ambient. This temperature sensitivity must be accounted for in bias circuit design to prevent thermal runaway in power transistors.

Variables

  • Vbe — Base-emitter voltage at operating temperature (V)
  • Vbe_ref — Vbe at reference temperature (V)
  • ΔT — Temperature change from reference (°C)

Practical Notes

The -2 mV/°C coefficient is an approximation that works well from -40°C to +125°C. The actual relationship is: Vbe = (kT/q) × ln(Ic/Is), where Is doubles approximately every 10°C. Bandgap references combine this negative tempco with the positive tempco of ΔVbe between two transistors to produce a temperature-independent 1.2V reference.

Symbols and units

Symbol Meaning Default unit Accepted units
Vbe Vbe at Temp mV pV, nV, µV, mV, V, kV
Vbe_ref Vbe Reference mV pV, nV, µV, mV, V, kV
dT Temperature Change °C °C

Step by step

  1. 1. What you know: Vbe Reference 1.32 V, Temperature Change 50 °C
  2. 2. The relation: Vbe(T) = Vbe_ref − 0.002 × ΔT
  3. 3. Substitute: Vbe_ref = 1.32 V, dT = 50 °C
  4. 4. Result: Vbe at Temp = 1.22 kV

Worked examples

Minimum range

Given: Vbe Reference 22 mV, Temperature Change 2.5 °C

Result: Vbe at Temp = 17 V

Low range

Given: Vbe Reference 0.22 V, Temperature Change 25 °C

Result: Vbe at Temp = 0.17 kV

Typical

Given: Vbe Reference 1.32 V, Temperature Change 50 °C

Result: Vbe at Temp = 1.22 kV

High range

Given: Vbe Reference 1.98 V, Temperature Change 85 °C

Result: Vbe at Temp = 1.81 kV

Maximum range

Given: Vbe Reference 19.8 V, Temperature Change 850 °C

Result: Vbe at Temp = 18.1 kV

How Vbe at Temp changes with Vbe Reference

Vbe Reference (input) Vbe at Temp (result)
0.29 V 70 V
0.725 V 0.505 kV
1.45 V 1.23 kV
2.175 V 1.955 kV
2.9 V 2.68 kV
4.35 V 4.13 kV
5.8 V 5.58 kV
11.6 V 11.38 kV
20.3 V 20.08 kV
29 V 28.78 kV

The same result in other units

Unit Value
mV 1220000
V 1220
kV 1.22

Embed this calculator

Paste this into any page. It keeps working when this page updates, and credits the source.

<iframe src="https://vbatpower.com/embed/bjt-vbe-temp/" width="100%" height="460" style="border:1px solid #1f2a37;border-radius:12px" loading="lazy" title="BJT Vbe vs Temperature"></iframe>
<p><a href="https://vbatpower.com/formulas/bjt-vbe-temp/">BJT Vbe vs Temperature</a> Calculator by vbatpower.com</p>

Frequently asked questions

How do you calculate BJT Vbe vs Temperature?

Use Vbe(T) = Vbe_ref − 0.002 × ΔT. With Vbe Reference 1.32 V, Temperature Change 50 °C, Vbe at Temp works out to 1.22 kV.

How do you calculate vbe temp coefficient?

Rearrange for Vbe at Temp: with Vbe Reference 0.22 V, Temperature Change 25 °C, Vbe at Temp is 0.17 kV.

What is the formula for BJT Vbe vs Temperature?

The formula is Vbe(T) = Vbe_ref − 0.002 × ΔT. The base-emitter voltage of a BJT decreases approximately 2 mV per degree Celsius increase in temperature.

What units does BJT Vbe vs Temperature use?

Vbe at Temp is shown in mV, V, kV. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

All Semiconductors formulas →
MOSFET Conduction Loss MOSFET Switching Loss BJT Total Dissipation Diode Power Loss Zener Regulation Resistor Transistor Current Gain (β) MOSFET Gate Drive Power MOSFET Rds(on) vs Temperature

Need more features?

Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.

Try the App