Advanced PN Junction Current Calculator

Calculator Inputs

The page stays single-column, while the input grid becomes 3, 2, or 1 columns by screen size.

Saturation Input Mode

Choose how the model builds the effective saturation current.

Applied Voltage (V)

Use positive values for forward bias and negative values for reverse bias.

Ideality Factor n

Typical values often lie between 1 and 2.

Temperature Value

Use kelvin or Celsius, then select the matching unit.

Temperature Unit

Thermal voltage is computed from the converted kelvin value.

Saturation Current Is (A)

Enter the reverse saturation current directly.

Saturation Current Density Js (A/cm²)

Use this when your data sheet gives current density.

Junction Area (cm²)

Area is used for current density and direct density mode.

Series Resistance Rs (Ω)

This accounts for lead and bulk resistance effects.

Shunt Resistance Rsh (Ω)

Lower values increase leakage through the parallel branch.

Graph Sweep Start (V)

This is the first voltage point for the I–V curve.

Graph Sweep End (V)

This is the last voltage point for the I–V curve.

Graph Points

Use 25 to 500 points for the plotted curve.

Plotly Graph

The chart shows current in milliamps across the selected voltage sweep. The red marker identifies the submitted operating point.

Example Data Table

Case	Voltage (V)	Temperature (K)	n	Is (A)	Rs (Ω)	Rsh (Ω)	Area (cm²)	Computed Current (A)	Computed Current (mA)
Example 1	0.65	300	1.8	2.0e-9	1.5	2.0e5	0.20	2.175783e-3	2.175783
Example 2	0.72	300	2.0	1.0e-12	1.0	1.0e6	0.10	1.836136e-6	0.001836
Example 3	0.55	325	1.6	3.0e-10	0.8	5.0e5	0.15	6.524271e-5	0.065243

Formula Used

This calculator models a practical pn junction with the Shockley equation and optional resistive effects.

Thermal voltage: Vt = kT / q
Effective saturation current: Is,eff = Is or Is,eff = Js × Area
Junction voltage: Vj = V − I × Rs
Diode branch current: Id = Is,eff × (exp(Vj / (nVt)) − 1)
Shunt branch current: Ish = Vj / Rsh
Total current: I = Id + Ish
Current density: J = I / Area
Small-signal resistance: rd ≈ 1 / gd, where gd = Is,eff × exp(Vj / (nVt)) / (nVt)

Because series resistance makes the equation implicit, the script solves current numerically with Newton-Raphson iteration.

How to Use This Calculator

Select whether you want to enter direct saturation current or current density with junction area.
Enter applied voltage, temperature, ideality factor, and junction area.
Add series and shunt resistance values for a more realistic junction model.
Choose graph sweep limits and the number of points.
Press Calculate Current to show the operating result above the form.
Review the summary cards, parameter table, and the plotted I–V curve.
Use the CSV button to export the summary and plotted data points.
Use the PDF button to save the visible result block for reporting or documentation.

Frequently Asked Questions

1) What equation does this calculator use?

It uses the Shockley diode equation with optional series and shunt resistance. That combination gives a practical pn junction model instead of a purely ideal one.

2) Why does temperature change the current?

Temperature changes thermal voltage and strongly affects exponential conduction. Higher temperature often increases carrier activity and alters the current at the same applied voltage.

3) What is saturation current?

Saturation current is the small reverse-bias current scale in the diode equation. It is usually tiny, but it strongly influences the forward current because it appears inside the exponential model.

4) When should I use current density mode?

Use current density mode when your source gives current per unit area. The calculator multiplies that density by junction area to build the effective saturation current.

5) What do series and shunt resistance represent?

Series resistance represents bulk and contact losses. Shunt resistance represents leakage around the junction. Together they make the predicted current more realistic for measured devices.

6) Does this model include avalanche or Zener breakdown?

No. The calculator handles reverse leakage within the diode equation and shunt branch only. It does not apply a dedicated avalanche or Zener breakdown model.

7) Why is the result solved numerically?

Once series resistance is included, current appears on both sides of the equation. A direct closed-form expression is no longer convenient, so the script uses iteration.

8) Can this calculator help in labs or device comparisons?

Yes. It is useful for checking operating points, comparing parameter sensitivity, plotting I–V behavior, and exporting results for reports, notes, or design reviews.