MOSFET Body Diode Loss Calculator

Calculate body-diode conduction and reverse-recovery losses in synchronous rectifiers. For buck converters and motor-drive inverters where dead-time forces body-diode conduction.

Calculator Electronics Updated Apr 23, 2026
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How to Use
  1. Enter Vf (body diode forward voltage), dead-time duration, load current, and switching frequency.
  2. Enter Qrr (reverse recovery charge from datasheet) and DC bus voltage.
  3. Tool computes conduction loss + recovery loss.
Input
V
ns
A
Hz (kHz OK)
nC
V
Presets
Loss Breakdown
Conduction
—mW
Recovery
—mW
Total
—mW
% of Iload·V
—%

Show Work

Enter values.

Formulas

Conduction
P_cond = Vf · I · t_d · f_sw · 2
Both rising + falling dead-time.
Recovery
P_rec = Qrr · V_bus · f_sw
Each switching cycle.
Total
P_total = P_cond + P_rec
Per MOSFET.
Mitigation
Schottky in parallel
Bypass body diode during dead-time.
Adaptive dead
Minimize t_d
Modern drivers sense Vds to minimize dead-time.
Scaling
P_rec ∝ f_sw
Dominates at high frequency.

History of Body-Diode Conduction

The parasitic body diode in DMOS power transistors - formed by the junction between source/body and drain - became a performance limitation when power MOSFETs displaced bipolar transistors in switching supplies in the late 1970s. Early MOSFETs had slow body diodes (trr > 500 ns) that caused shoot-through and EMI. Modern trench-gate MOSFETs reduce Qrr 5-10x. SiC and GaN devices eliminate body-diode reverse recovery entirely - a major efficiency gain driving their adoption in high-frequency converters.

About This Calculator

Enter Vf body diode (typical 0.7-1.2 V, datasheet), dead-time t_d (gate-driver spec, 10-200 ns), load current, switching frequency, Qrr (reverse recovery charge), and DC bus voltage. The tool computes conduction loss during dead-time and recovery loss per switching cycle.

To reduce body-diode losses: choose low-Qrr MOSFETs (trench or super-junction), add Schottky in parallel, or use adaptive dead-time gate drivers. Everything runs client-side.

Frequently Asked Questions

Why body diode?

In a synchronous rectifier (e.g., buck low-side MOSFET), during dead-time the body diode conducts instead of the channel. High Vf (~1 V vs ~0.1 V channel) causes extra loss.

Recovery loss?

When the high-side turns on, the low-side body diode must recover — the Qrr charge flows through the high-side MOSFET as shoot-through, dissipating Qrr·V_bus·f each switching cycle.

Schottky in parallel?

Adding an external Schottky across the MOSFET body diode reduces Vf during dead-time and bypasses much of the recovery charge. Common in motor drives where body-diode losses are a significant % of total.

Common Use Cases

Buck Converter

Low-side MOSFET body diode conducts during dead-time; typical 1-3% efficiency loss at high current.

Motor Drive Inverter

Body diode conducts commutation current; Qrr loss dominates above 10 kHz.

Flyback Sync Rect

Replace Schottky output diode with synchronous MOSFET for +2-3% efficiency.

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