Diode Forward Voltage Calculator Formula

Understand the math behind the diode forward voltage calculator. Each variable explained with a worked example.

Use the Diode Forward Voltage Calculator

Formulas Used

Output Voltage

output_voltage = supply_voltage - diode_vf

Diode Power Dissipation

diode_power_mw = diode_vf * load_current_a * 1000

Variables

VariableDescriptionDefault
supply_voltageSupply Voltage(V)5
diode_vfDiode Forward Voltage(V)0.7
load_current_maLoad Current(mA)100
load_current_aDerived value= load_current_ma / 1000calculated

How It Works

Diode Forward Voltage Drop

When current flows through a diode, it drops a nearly constant forward voltage V_f.

Formula

V_out = V_supply - V_f

P_diode = V_f x I_load

Silicon diodes drop about 0.7 V, Schottky diodes 0.2-0.4 V, and LEDs 1.8-3.3 V depending on color.

Worked Example

A silicon diode (0.7 V drop) in a 5 V circuit carrying 100 mA.

supply_voltage = 5diode_vf = 0.7load_current_ma = 100
  1. 01V_out = 5 - 0.7 = 4.3 V
  2. 02I_load = 100 / 1000 = 0.1 A
  3. 03P_diode = 0.7 x 0.1 = 0.07 W = 70 mW

Ready to run the numbers?

Open Diode Forward Voltage Calculator