Calculator
Example Data Table
| Diode | Current | Temperature | Typical Drop | Common Use |
|---|---|---|---|---|
| Silicon PN | 10 mA | 25 °C | 0.65 V to 0.75 V | Signal rectifier |
| Schottky | 100 mA | 25 °C | 0.20 V to 0.45 V | Low loss clamp |
| Germanium | 1 mA | 25 °C | 0.20 V to 0.35 V | Detector circuit |
| Red LED | 20 mA | 25 °C | 1.8 V to 2.2 V | Indicator light |
| White LED | 20 mA | 25 °C | 2.8 V to 3.5 V | Lighting circuit |
Formula Used
Constant model: VD = VF + TC × (T - 25) ÷ 1000
Shockley model: VD = nVT ln(I ÷ IS + 1) + IRS
Hybrid model: VD = VF + nVT ln(I ÷ IREF) + TC × (T - 25) ÷ 1000 + IRS
Thermal voltage: VT = kT ÷ q
Total drop: VTOTAL = N × VD
Power: P = V × I
For supply and resistor mode, the calculator solves VS = IR + N × VD by iteration.
How to Use This Calculator
Select the diode type. Pick the calculation model that matches your data. Use the constant model for quick checks. Use Shockley when you know saturation current and ideality factor. Use the hybrid model when a datasheet gives forward voltage at a test current.
Choose known current when current is already fixed. Choose supply with series resistor when you want the calculator to solve current. Enter the number of series diodes, temperature, and custom values. Press calculate. Then download the CSV or PDF result if you need a record.
Diode Voltage Drop Calculator Guide
Why diode drop matters
A diode is not an ideal switch. It needs forward voltage before useful current flows. That drop changes with material, current, temperature, and small internal resistance. A silicon signal diode may sit near 0.7 volts. A Schottky diode can be far lower. An LED may need much more voltage. This calculator helps you compare those cases before you build or test a circuit.
Better design choices
Voltage drop affects power loss and available load voltage. In a rectifier, every conducting diode wastes energy as heat. In a protection circuit, the drop decides how much voltage reaches the protected device. In an LED string, the total drop tells you what supply and resistor are needed. Seeing current, power, resistor loss, and dynamic resistance together makes design review faster.
Model options
The constant model is simple. It is useful for quick checks and beginner schematics. The Shockley model estimates junction voltage from current, ideality factor, saturation current, and temperature. The hybrid model starts from a nominal voltage at a reference current. It then adjusts for current and temperature. That option is often practical when a datasheet gives typical forward voltage at a known test current.
Temperature and heat
Forward voltage usually falls as junction temperature rises. Silicon devices often use about minus two millivolts per degree Celsius. LEDs and Schottky parts may use different values. Power is current multiplied by voltage. Higher power means more heat, which can change the drop again. Use the result as a design estimate, not as a substitute for a full thermal test.
Using the results
Choose the diode type first. Select a calculation mode. Use known current when you already know the operating current. Use supply and resistor mode when the circuit sets current through a resistor. Enter custom values when your datasheet differs from the preset. Review total voltage drop and total power. Export the CSV or PDF record for lab notes, reports, or client documentation.
Practical limits
Real circuits include tolerances, pulsed loads, wiring resistance, aging, and manufacturing spread. Always keep margin. Check maximum current, reverse voltage, package power, and temperature rating. For critical products, confirm the calculator result with measurement and the datasheet.
FAQs
What is diode voltage drop?
It is the forward voltage across a conducting diode. The value depends on diode material, current, temperature, and device construction.
Why is a Schottky diode drop lower?
A Schottky diode uses a metal semiconductor junction. It usually needs less forward voltage than a silicon PN junction at similar current.
Does diode voltage drop change with current?
Yes. Higher current normally increases forward voltage. The rise is not linear, so advanced models use logarithmic junction equations.
How does temperature affect the drop?
Most silicon diode forward voltage decreases as temperature rises. A common estimate is about two millivolts per degree Celsius.
Can I calculate LED resistor value here?
Yes. Use supply with series resistor mode. Adjust resistance until current and power match the desired LED operating point.
Which model should I choose?
Use constant mode for rough checks. Use Shockley for detailed junction data. Use hybrid mode for common datasheet values.
Why is dynamic resistance shown?
Dynamic resistance shows the small signal slope around the operating point. It helps estimate ripple, signal response, and bias behavior.
Are the results exact?
No. Real parts vary by tolerance, heat, batch, and package. Always compare the result with the diode datasheet and measurements.