Calculator
Formula Used
The calculator rearranges the Shockley diode equation.
I = Is × [exp(Vj / nVt) − 1]
Is = I / [exp(Vj / nVt) − 1]
For automatic thermal voltage, it uses this relation.
Vt = kT / q
Where I is diode current, Is is reverse saturation current, Vj is corrected junction voltage, n is ideality factor, and Vt is thermal voltage.
Temperature projection uses this common approximation.
Is₂ = Is₁ × (T₂ / T₁)³ × exp[−Eg / k × (1 / T₂ − 1 / T₁)]
How to Use This Calculator
- Select forward mode for a measured forward voltage and current.
- Select reverse mode for a measured reverse leakage value.
- Enter current, voltage, temperature, and ideality factor.
- Use automatic thermal voltage unless you need a fixed value.
- Add series resistance for higher current forward measurements.
- Enter junction area when current density is needed.
- Set a target temperature for projected leakage current.
- Press Calculate, then download the CSV or PDF report.
Example Data Table
| Mode | Current | Voltage | Temperature | Ideality | Approximate Is |
|---|---|---|---|---|---|
| Forward | 10 mA | 0.70 V | 25 °C | 1.8 | 1.28e-8 A |
| Forward | 1 mA | 0.62 V | 25 °C | 1.9 | 3.08e-9 A |
| Reverse | 50 nA | 5 V | 25 °C | 2.0 | 5.00e-8 A |
Reverse Saturation Current Overview
Reverse saturation current is the small current linked with minority carriers inside a diode junction. It is often called Is. The value is important because it shapes the full diode current curve. It also affects leakage, switching, noise, and thermal stability. A tiny change can become large when temperature rises.
Why It Matters
Designers use Is when they model rectifiers, signal diodes, LEDs, and transistor junctions. The value helps predict forward current at a chosen voltage. It also helps compare leakage in reverse bias. In precision circuits, leakage may create offset errors. In power circuits, it may add heat. For sensor circuits, it can shift calibration.
Practical Measurement Notes
A forward measurement is often easier than a deep reverse measurement. Measure diode voltage and current at a stable temperature. Then solve the Shockley equation backward. For reverse leakage, use the reverse current magnitude and reverse voltage magnitude. Keep the current range within the meter resolution. Use guarded wiring for nanoamp readings. Avoid touching leads during sensitive tests. Body leakage can disturb the result.
Temperature and Ideality
Temperature has a strong effect on Is. Thermal voltage rises with absolute temperature. The saturation current usually rises much faster. The ideality factor describes how close the junction is to an ideal diffusion diode. A value near one often fits diffusion current. A value near two may fit recombination current. Real parts can shift across regions.
Using the Result
This calculator gives the estimated Is, current density, exponent term, and projected temperature value. The area entry is optional. It helps compare devices of different junction sizes. Series resistance is also optional. It can improve forward calculations when current is high. For low current leakage work, the correction may be tiny. Always compare the estimate with datasheet limits and lab conditions.
Limitations
The Shockley model is a useful starting point. It does not include avalanche breakdown, high injection, surface leakage, self heating, or package contamination. The estimate is best when the measured point sits in a normal exponential region. Use several measured points when accuracy matters. Consistent estimates mean the model is working well.
Record instrument range and settling time. Note polarity and temperature for audits. Retest outliers before final use.
FAQs
What is reverse saturation current?
It is the small diode current linked with minority carriers. It appears in the Shockley diode equation as Is. It strongly affects leakage and the exponential current curve.
Can I use forward bias data?
Yes. Forward voltage and current can estimate Is by rearranging the diode equation. Use a stable bias point in the exponential region for better accuracy.
Can I use reverse leakage data?
Yes. Select reverse mode and enter leakage current magnitude. For strong reverse bias below breakdown, the leakage value is often close to Is.
What ideality factor should I enter?
Use a measured value when possible. Silicon diodes often fall between one and two. Real devices vary with current, temperature, and construction.
Why does temperature matter so much?
Temperature changes thermal voltage and carrier generation. Reverse saturation current usually rises quickly as temperature increases. This can affect leakage, noise, and power loss.
What is current density?
Current density divides Is by junction area. It helps compare different devices when their physical sizes are not the same.
Should I include series resistance?
Include it when forward current is high enough to cause a noticeable voltage drop. For small leakage measurements, the correction is usually minor.
Is this calculator valid near breakdown?
No. Avalanche or Zener breakdown needs a different model. Use this calculator for normal diode operation away from breakdown and high injection regions.