Pick your Diode Type, enter your Forward Current (If), Supply Voltage, Temperature, and optionally fine-tune the Ideality Factor (n) and Saturation Current (Is) — the calculator returns the Forward Voltage (Vf), along with your Required Series Resistance, Diode Power Dissipation, and recommended Resistor Power Rating.
Forward Voltage (Vf)
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Required Series Resistance
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Diode Power Dissipation
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Resistor Power Rating
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Forward voltage drop (Vf) is the voltage that appears across a diode when it conducts current in the forward direction. It's typically 0.7V for silicon diodes, 0.3V for germanium diodes, and 1.8-3.3V for LEDs depending on color.
Forward voltage decreases with increasing temperature at a rate of approximately -2mV/°C for silicon diodes. This temperature coefficient is important for thermal compensation in circuits.
The ideality factor (n) represents how closely a real diode follows the ideal diode equation. It ranges from 1.0 for perfect diodes to 2.0 for diodes with significant recombination effects. Most silicon diodes have n between 1.0 and 1.2.
LEDs have a very steep current-voltage characteristic, so small voltage changes cause large current changes. A series resistor limits current to prevent LED damage and ensures stable operation.
Saturation current is the reverse current that flows when a diode is reverse-biased. It's typically very small (picoamperes to nanoamperes) and doubles approximately every 10°C temperature increase.
The ideal diode equation is quite accurate for forward-biased silicon diodes at normal current levels. However, it becomes less accurate at very low or very high currents, or when series resistance effects become significant.
Choose a resistor with power rating 2-10 times higher than the calculated power dissipation to ensure reliable operation and prevent overheating. This provides adequate safety margin for component variations and environmental factors.