How this calculator works
The ideal junction law grows exponentially in forward bias and approaches minus the saturation current in reverse bias. Thermal voltage is kT/q, about 25.85 mV at 300 K. Saturation current changes strongly with temperature and device construction, so it must be supplied for the operating conditions. The numerical calculation uses expm1 and log1p to retain accuracy near zero voltage and current.
Formula
I = Is [exp(Vd/(n Vt))-1]; Vd = n Vt ln(1+I/Is); Vt = kT/q.
Worked example
With Is = 1 mA, n = 1 and Vt = 25 mV, Vd = 25 ln(2) mV gives I = 1 mA. With n = 2 and I = 3 mA, the voltage is 50 ln(4) = 69.314718 mV.
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Frequently asked questions
Is a Shockley diode a four-layer device?
The name can refer to a separate four-layer switching device. This calculator uses the Shockley junction current-voltage equation.
Can it predict avalanche breakdown?
No. Reverse breakdown requires additional device-specific modelling.
Is saturation current a constant for every temperature?
No. Use a value appropriate to the junction temperature; it can change by orders of magnitude.