MOSFET Gate Drive Headroom

Vmargin = Vgs − Vth

Quick answer

This calculator solves V_margin = V_gs − V_th for Gate Headroom. With Gate-Source Voltage 26.4 V, Threshold Voltage 56.4 V, the result is -30 V. It solves in 3 directions, so you can enter the values you have and get the one you need.

Calculator

Gate Headroom (V)
—

Formula

V_margin = V_gs − V_th

Description

The gate drive voltage must exceed the threshold voltage by a sufficient margin to fully enhance the MOSFET and achieve its rated Rds(on). A MOSFET specified at Rds(on) = 10 mΩ at Vgs = 10 V may have Rds(on) = 20 mΩ at Vgs = 4.5 V and may not turn on at all if Vgs barely exceeds Vth. The margin between Vgs and Vth determines how deeply the MOSFET is enhanced and directly affects conduction losses. Logic-level MOSFETs (Vth = 1-2 V) can be driven directly from 3.3 V or 5 V logic, while standard MOSFETs (Vth = 2-4 V) require a gate driver with 8-12 V output.

Variables

  • V_margin — Gate drive headroom above threshold (V)
  • V_gs — Applied gate-to-source voltage (V)
  • V_th — Gate threshold voltage (V)

Practical Notes

Vth varies with temperature (typically −3 to −7 mV/°C), so the margin decreases as the MOSFET heats up. Always check Rds(on) at the actual Vgs you can provide, not just the datasheet headline value. For high-side N-channel MOSFETs, a bootstrap or charge pump circuit is needed to generate Vgs above the source voltage. GaN FETs have lower Vth (1-2 V) and require more precise gate drive voltage control.

Symbols and units

Symbol Meaning Default unit Accepted units
Vmargin Gate Headroom V pV, nV, µV, mV, V, kV
Vgs Gate-Source Voltage V pV, nV, µV, mV, V, kV
Vth Threshold Voltage V pV, nV, µV, mV, V, kV

Step by step

  1. 1. What you know: Gate-Source Voltage 26.4 V, Threshold Voltage 56.4 V
  2. 2. The relation: V_margin = V_gs − V_th
  3. 3. Substitute: Vgs = 26.4 V, Vth = 56.4 V
  4. 4. Result: Gate Headroom = -30 V

Worked examples

Minimum range

Given: Gate-Source Voltage 0.726 V, Threshold Voltage 1.55 V

Result: Gate Headroom = -0.824 V

Low range

Given: Gate-Source Voltage 7.26 V, Threshold Voltage 15.5 V

Result: Gate Headroom = -8.24 V

Typical

Given: Gate-Source Voltage 26.4 V, Threshold Voltage 56.4 V

Result: Gate Headroom = -30 V

High range

Given: Gate-Source Voltage 0.506 kV, Threshold Voltage 1.08 kV

Result: Gate Headroom = -0.574 kV

Maximum range

Given: Gate-Source Voltage 5.06 kV, Threshold Voltage 10.8 kV

Result: Gate Headroom = -5.74 kV

Solving for each variable

Solve for Gate Headroom

Gate-Source Voltage 0.726 V, Threshold Voltage 1.55 V → -0.824 V

Solve for Gate-Source Voltage

Gate Headroom 0.33 V, Threshold Voltage 1.55 V → 1.88 V

Solve for Threshold Voltage

Gate Headroom 0.33 V, Gate-Source Voltage 0.726 V → 0.396 V

How Gate Headroom changes with Gate-Source Voltage

Gate-Source Voltage (input) Gate Headroom (result)
5.81 V -118.2 V
14.53 V -109.5 V
29.05 V -94.95 V
43.58 V -80.42 V
58.1 V -65.9 V
87.15 V -36.85 V
116.2 V -7.8 V
0.2324 kV 108.4 V
0.4067 kV 0.2827 kV
0.581 kV 0.457 kV

The same result in other units

Unit Value
mV -30000
V -30
kV -0.03

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/mosfet-vgs-headroom/" width="100%" height="460" style="border:1px solid #1f2a37;border-radius:12px" loading="lazy" title="MOSFET Gate Drive Headroom"></iframe>
<p><a href="https://vbatpower.com/formulas/mosfet-vgs-headroom/">MOSFET Gate Drive Headroom</a> Calculator by vbatpower.com</p>

Frequently asked questions

How do you calculate MOSFET Gate Drive Headroom?

Use V_margin = V_gs − V_th. With Gate-Source Voltage 26.4 V, Threshold Voltage 56.4 V, Gate Headroom works out to -30 V.

How do you calculate calculate voltage headroom?

Rearrange for Gate Headroom: with Gate-Source Voltage 7.26 V, Threshold Voltage 15.5 V, Gate Headroom is -8.24 V.

What is the formula for MOSFET Gate Drive Headroom?

The formula is V_margin = V_gs − V_th. The gate drive voltage must exceed the threshold voltage by a sufficient margin to fully enhance the MOSFET and achieve its rated Rds(on).

How do you find Gate-Source Voltage when you know the other values?

Rearrange for Gate-Source Voltage: with Gate Headroom 0.33 V, Threshold Voltage 1.55 V, Gate-Source Voltage is 1.88 V.

How do you find Threshold Voltage when you know the other values?

Rearrange for Threshold Voltage: with Gate Headroom 0.33 V, Gate-Source Voltage 0.726 V, Threshold Voltage is 0.396 V.

What units does MOSFET Gate Drive Headroom use?

Gate Headroom 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