Calculate diode power dissipation, forward current, or forward voltage, and check if a diode power rating meets the chosen safety margin.

Use steady forward voltage and current.

P = V × I is steady conduction loss. Confirm temperature/thermal derating, reverse voltage, current, surge and switching limits in the device datasheet; a power comparison alone cannot select a safe diode.

Related Calculators

Diode Selection Formula

The following formula estimates steady forward-conduction power dissipation. The required diode rating must also account for the chosen allowance, actual temperature and mounting, and other device limits.

P = I × Vf

Variables:

  • P is the steady forward-conduction power dissipation (watts)
  • I is the current through the diode (amperes)
  • Vf is the forward voltage of the diode (volts)

To estimate steady conduction loss, multiply current by forward voltage at that current. This does not establish a safe device rating: check datasheet thermal derating, reverse voltage, current, surge and switching limits.

What is a Diode Selection?

Diode selection is the process of choosing a diode that can safely and efficiently operate in a given electrical circuit. The selection is based on several parameters, including the maximum current the diode can handle (forward current), the maximum reverse voltage it can withstand without breaking down (reverse voltage), and the power rating. The power rating is particularly important as it determines the amount of power the diode can dissipate without overheating.

How to Calculate Power Rating for Diode Selection?

The following steps estimate steady conduction loss for a diode power comparison.

  1. First, determine the current through the diode (I) in amperes.
  2. Next, determine the forward voltage of the diode (Vf) in volts.
  3. Next, gather the formula from above = P = I * Vf.
  4. Finally, calculate the conduction loss (P) in watts, then compare its chosen allowance with the applicable derated rating.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Current through the diode (I) = 2 amperes

Forward voltage of the diode (Vf) = 1.2 volts. The conduction loss is 2 × 1.2 = 2.4 W; a 2× allowance is 4.8 W, before checking the device’s other limits.