Diode Power Loss

Formula

Description

A forward-biased diode drops a relatively constant voltage (Vf) regardless of current, so its power dissipation is simply the product of forward voltage and forward current. Silicon diodes typically drop 0.6-0.7V, Schottky diodes 0.2-0.45V, and LEDs 1.8-3.4V depending on color. In power supply rectification, diode losses can be significant: a 1A load through a silicon diode wastes 0.7W, while a Schottky diode wastes only 0.3W. This is why synchronous rectification using MOSFETs is preferred in high-efficiency power supplies.

Variables

• P — Power dissipation (W)
• Vf — Forward voltage drop (V)
• If — Forward current (A)

Practical Notes

For more accurate calculations at high currents, use the piecewise model: P = Vf0 × If + Rd × If², where Vf0 is the threshold voltage and Rd is the dynamic resistance. Schottky diodes have lower Vf but higher leakage current and lower maximum reverse voltage than silicon diodes.