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Shockley Diode Calculator

Created by Álvaro Díez
Reviewed by Bogna Szyk and Steven Wooding
Last updated: Jan 26, 2024

The Shockley diode calculator allows you to calculate either the voltage drop or the current flowing through a real diode, knowing the other value. It allows you to calculate I-V values and helps you understand how the transistor works in either forward or reverse bias. The Shockley diode calculator can obtain values for both a real (imperfect) and an ideal diode using the Shockley diode equation (also called the diode law).

What are real and ideal diodes?

A diode is an electronic component that only allows the electrical current to flow in one direction. It is made by putting in contact an n-type and a p-type semiconductor crystal. The physics behind the behavior of the p-n junction is complicated. Still, the resulting diode can almost perfectly block the current flowing in one direction of the electrical circuit while allowing it to flow normally in the other direction. The Shockley diode calculator helps you calculate the current-voltage (I-V) relationship in both cases.

As is common in science, there are imperfections arising from the manufacturing processes and the imperfect technology at our disposal; these imperfections are parametrized by the emission coefficient (n) that typically ranges between 1 and 2 (1 being an ideal diode). The ideal diode is, as the name implies, an idealization in which the diode is assumed to have no imperfections.

In most cases, a real diode can be assumed to behave like an ideal diode without a significant loss in accuracy. However, for exact calculations, the user is welcome to change the emission coefficient from an ideal diode (1) to that of the diode they are working with. This emission coefficient is a parameter of the diode and should be given as part of its specifications.

Shockley diode equation and how the calculator works

The Shockley diode calculator uses the Shockley diode equation (shown below) that has 5 different parameters, 4 of which should be input by the user.

I=IS(eVDnVT1)\large I = I_{\rm S}\left(e^\frac{V_{\rm D}}{nV_{\rm T}} - 1 \right)

Three of these five parameters are what you could call "specifications of the diode," meaning they are intrinsic parameters of a particular diode:

  1. nnEmission coefficient is a parametrization of the imperfections of the diode. Typically ranges from 1 (ideal diode) to 2. It is set to 1 by default in the Shockley diode calculator.

  2. ISI_{\rm S} – (Reverse) saturation current is the intrinsic current present in all diodes (including the ideal diode), and it is almost only dependent on the temperature. For a more detailed explanation, we recommend the Wikipedia article on reverse saturation current.

  3. VTV_{\rm T} – Thermal voltage is the internal voltage in the diode when disconnected from the circuit. It is caused by the temperature and the properties of the p-n junction inside the diode.

The other 2 are experimental variables, the ones that are typically changed during a laboratory experiment.

  1. VDV_{\rm D}Voltage drop is the voltage difference between the connections of the diode to the circuit.

  2. IICurrent flowing through the diode.

How to use the Shockley diode calculator

The Shockley diode calculator is a simple tool that allows you to obtain information about a real/ideal diode. The typical use case would be to find the I-V curve of a particular diode from its specifications. However, the possibilities increase significantly when used in conjunction with other calculators.

For example, by using this Shockley diode calculator in conjunction with the Ohm's law calculator, you can obtain the values of the resistance and power draw of the real/ideal diode for any value of current or voltage. This method is advantageous since a diode does not follow a linear relationship between the current flowing through it and the voltage drop. Its resistance is not constant but depends on the voltage/current applied and the temperature.

Other uses might include fast simulation of simple circuits and their properties. It is true that as an electrical circuit to be simulated grows in complexity, it becomes more time efficient to use dedicated software (such as LabView, LTspice...) for such a task. Nevertheless, in the case of one-time simulations of basic circuits, this Shockley diode calculator – together with the LED resistor calculator and the voltage drop calculator – provides a straightforward way to perform accurate simulations of circuits involving diodes (including several LEDs) and to take into account the effects of the wiring/resistances present in them.

Álvaro Díez
Emission coefficient
Saturation current
Thermal voltage
Voltage drop
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