Diode Calculator

About Diode Calculator

The Diode Calculator helps you analyze diode behavior in circuits by calculating voltage drop, current flow, and required resistor values. This free online tool supports silicon, germanium, Schottky diodes, and LEDs, making it perfect for circuit design, analysis, and troubleshooting.

Diode Circuit Formulas

Current Calculation:

I = (Vs - Vf) / R

Resistor Calculation:

R = (Vs - Vf) / I

Where Vs = Supply Voltage, Vf = Forward Voltage, R = Resistance, I = Current

Common Diode Types & Forward Voltages

Silicon Diode

Forward Voltage: ~0.7V

Most common type (1N4001, 1N4007)

Germanium Diode

Forward Voltage: ~0.3V

Lower voltage drop (1N34A)

Schottky Diode

Forward Voltage: ~0.3V

Fast switching (1N5817, 1N5819)

LED

Forward Voltage: 1.8-3.4V

Depends on color (red ~2V, blue/white ~3.2V)

How to Use This Calculator

Select Calculation Mode: Choose what you want to calculate (current, resistor, or voltage drop)
Enter Supply Voltage: The voltage source powering your circuit
Enter Forward Voltage: Use presets for common diode types or enter custom value
Enter Additional Parameters: Resistor value (for current) or desired current (for resistor)
View Results: Get instant calculations with step-by-step breakdown

Important Notes

Forward voltage: The voltage drop across a diode when it's conducting. This is approximately constant for a given diode type.

Reverse bias: This calculator assumes forward-biased operation. In reverse bias, diodes block current (except for small leakage).

Power dissipation: Always use a resistor with adequate power rating (at least 2× calculated power).

Temperature effects: Forward voltage decreases slightly with temperature (~-2mV/°C for silicon).

Example Calculations

Example 1: Calculate Current

Supply: 5V | Diode: 0.7V (Silicon) | Resistor: 1kΩ

Result: 4.3 mA

Example 2: Calculate Resistor for LED

Supply: 12V | LED: 2V | Desired Current: 20mA

Result: 500Ω → 510Ω standard (0.25W)

Example 3: Voltage Drop Analysis

Supply: 9V | Diode: 0.7V (Silicon)

Result: 0.7V drop, 8.3V remaining

Common Applications

✓ LED Circuits: Calculate current-limiting resistors for LED indicators
✓ Rectifier Circuits: Analyze voltage drops in AC-to-DC conversion
✓ Protection Circuits: Design reverse polarity and overvoltage protection
✓ Signal Processing: Calculate parameters for clipping and clamping circuits
✓ Power Supplies: Analyze diode behavior in voltage regulators
✓ Educational: Learn about diode characteristics and circuit analysis