What is Diode Current Equation?


Diode Current Equation

The diode current equation shows the relationship in between the current flow through diode as a function of the voltage applied across it. The current through the diode is does not change linearly with respect to applied voltage. The relation in between voltage and current has the exponential. The region behind of non-linear current is that the resistance of diode is temperature dependent. When the temperature increase the diode current is increases. The mathematically the diode current equation can be expressed as:

What-is-Diode-current-Equation-1 …………………(1)


  • I is the diode current
  • I0 is the dark saturation current,
  • q is the charge on the electron,
  • V is the voltage applied across the diode,
  • η is the (exponential) ideality factor.
  • K is the Boltzmann constant which is equal to K = 1.38 x 10-23   J/K
  • T is absolute temperature in Kelvin.

In diode current equation the two parameters require to be discussed in quite detail. These parameters are given below:

  • Dark Saturation Current, I0.
  • Exponential Ideality Factor, η.

Dark Saturation current:

When the diode is in reverse bias the current flow through the diode is called reverse saturation current. The region behind of flow of reverse current is due to minority carrier. The range of this current in μA to nA. It is an important parameter of a diode characteristic and indicates the amount of recombination which occurs within it.

That is the value of I0 will be high when recombination rate is high and vice versa. The dark saturation current is directly proportional to the absolute temperature and inversely proportional to the material quality.

Exponential Ideality Factor, η.

The exponential identical factor is the nearness of ideal diode, how accurately the diode follows the ideal diode equation. If the identical factor is 1 the diode is almost same as ideal diode. The identical factor for germanium is 1 diode and 2 silicon diode. This factor are depends on the following factor which are mention below-

  1. Electron Drift
  2. Diffusion
  3. Carrier Combination in the depletion region
  4. Doping Level
  5. Manufacturing Process
  6. Purity of the material

The value of η is “1” for Silicon diode and “2” for Germanium diode

When the diode is forward bias, the current through diode will be high in the range of milli ampere and the diode current equation becomes


On the other hand when the diode is reverse bias, the exponential term of the diode current equation is neglected and the current becomes:

I = – I0
Now let us understand the mode of diode current equation. When diode are operate at room temperature. In this case, T = 300 K, also, k= 1.38 × 10-23 Jk-1 and q = 1.6 × 10-19 C. Thus
q/KT = 1.6  × 10-19 / 1.38 × 10-23 × 300
= 0.003865 × 104
= 38.65 C J-1 or 38.65 V-1

At room temperature the diode equation becomes as-
I = – I0 e-v/0.025× η

Frequently ask question

How is diode current equation derived?

The diode has non liner device. The diode current is

I = – I0 e-v/0.025× η

What is meant by diode current?

The diode currant is show the relationship between the current flowing through the diode when we applied the voltage across the diode.

Why is diode current exponential?                                                

Initially when we applied the voltage through diode the current flow through it and the graph of current is slowly at first, then more quickly, and eventually very quickly. This occurs because the relationship between a diode’s forward voltage and its forward current is exponential rather than linear.

What is the approximate value of thermal voltage VT in the diode equation?

“The thermal voltage VT is approximately 25.8563 mV at 300 K (27 °C; 80 °F).

How does a diode effect current?

Fundamentally, a diode is a component that permits current to flow in a single direction and blocks it in the other direction. Diodes allow current to flow in one direction without the effects of any impedance, while entirely blocking all flow of current flow in the other.

Do diodes limit current?

What is a Current Limiting Diode? A Current Limiting Diode, also known as a “Current Regulating Diode” or a “Constant Current Diode”, per- forms quite a unique function. Similar to a Zener diode, which regulates voltage at a particular current, the CLD limits or regulates current over a wide voltage range.

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