Half-Bridge Dead Time

t_dead = Qgd / Igate

Quick answer

This calculator solves t_dead = Q_gd / I_gate for Dead Time. With Gate-Drain Charge 10 nC, Gate Drive Current 2 A, the result is 5 ns. It solves in 3 directions, so you can enter the values you have and get the one you need.

Calculator

Dead Time (ns)
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Formula

t_dead = Q_gd / I_gate

Description

In a half-bridge or full-bridge circuit, dead time is the mandatory delay between turning off one MOSFET and turning on the other to prevent shoot-through (both transistors on simultaneously, creating a short circuit from supply to ground). The minimum dead time must exceed the turn-off time of the MOSFET, which is dominated by the Miller plateau where the gate driver must remove the gate-drain charge Qgd. The actual dead time should include safety margin (typically 2-3x the calculated minimum) to account for component variation and temperature effects.

Variables

  • t_dead — Minimum dead time (s)
  • Q_gd — MOSFET gate-drain (Miller) charge (C)
  • I_gate — Gate driver sink current (A)

Practical Notes

Typical dead times: 50-200 ns for silicon MOSFETs, 20-50 ns for GaN FETs. During dead time, the inductor current flows through the body diode (or reverse channel in GaN), causing conduction loss and reverse recovery loss. Excessive dead time increases body diode loss and distorts the output waveform. Adaptive dead time control in modern gate drivers optimizes this trade-off automatically.

Symbols and units

Symbol Meaning Default unit Accepted units
t Dead Time ns ps, ns, µs, ms, s, min, h
Qgd Gate-Drain Charge nC pC, nC, µC, mC, C
Igate Gate Drive Current A pA, nA, µA, mA, A, kA

Step by step

  1. 1. What you know: Gate-Drain Charge 10 nC, Gate Drive Current 2 A
  2. 2. The relation: t_dead = Q_gd / I_gate
  3. 3. Substitute: Qgd = 10 nC, Igate = 2 A
  4. 4. Result: Dead Time = 5 ns

Worked examples

Minimum range

Given: Gate-Drain Charge 100 pC, Gate Drive Current 2 mA

Result: Dead Time = 50 ns

Low range

Given: Gate-Drain Charge 1 nC, Gate Drive Current 20 mA

Result: Dead Time = 50 ns

Typical

Given: Gate-Drain Charge 10 nC, Gate Drive Current 2 A

Result: Dead Time = 5 ns

High range

Given: Gate-Drain Charge 100 nC, Gate Drive Current 100 A

Result: Dead Time = 1 ns

Maximum range

Given: Gate-Drain Charge 1 µC, Gate Drive Current 1 kA

Result: Dead Time = 1 ns

Solving for each variable

Solve for Dead Time

Gate-Drain Charge 100 pC, Gate Drive Current 2 mA → 50 ns

Solve for Gate-Drain Charge

Dead Time 100 ps, Gate Drive Current 2 mA → 0.2 pC

Solve for Gate Drive Current

Dead Time 100 ps, Gate-Drain Charge 100 pC → 1 A

How Dead Time changes with Gate-Drain Charge

Gate-Drain Charge (input) Dead Time (result)
1 nC 0.5 ns
2.5 nC 1.25 ns
5 nC 2.5 ns
7.5 nC 3.75 ns
10 nC 5 ns
15 nC 7.5 ns
20 nC 10 ns
40 nC 20 ns
70 nC 35 ns
100 nC 50 ns

The same result in other units

Unit Value
ps 5000
ns 5
µs 0.005

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Frequently asked questions

How do you calculate Half-Bridge Dead Time?

Use t_dead = Q_gd / I_gate. With Gate-Drain Charge 10 nC, Gate Drive Current 2 A, Dead Time works out to 5 ns.

How do you calculate calculated off bridge time?

Rearrange for Dead Time: with Gate-Drain Charge 1 nC, Gate Drive Current 20 mA, Dead Time is 50 ns.

What is the formula for Half-Bridge Dead Time?

The formula is t_dead = Q_gd / I_gate. In a half-bridge or full-bridge circuit, dead time is the mandatory delay between turning off one MOSFET and turning on the other to prevent shoot-through (both transistors on simultaneously, creating a short circuit from supply to ground).

How do you find Gate-Drain Charge when you know the other values?

Rearrange for Gate-Drain Charge: with Dead Time 100 ps, Gate Drive Current 2 mA, Gate-Drain Charge is 0.2 pC.

How do you find Gate Drive Current when you know the other values?

Rearrange for Gate Drive Current: with Dead Time 100 ps, Gate-Drain Charge 100 pC, Gate Drive Current is 1 A.

What units does Half-Bridge Dead Time use?

Dead Time is shown in ps, ns, µs. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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