Diode equivalent circuit 

In this article, we explain the equivalent circuit of the diode. The diode is a semiconductor device that has applications at every electronic circuit, but when we analyzing the properties of the diode, it must be a complex process to done.

Here is the importance of equivalent circuits, we can easily derive the characteristics and behaviors of the diode with the equivalent circuit.


Significance of equivalent circuits 

We already know an equivalent is a model circuit for a component or a most complex circuit. An equivalent circuit is built with passive components such as a resistor, capacitor, or inductor.

The passive components can have the ability to store, oppose and convert the power into another form, that why they can make any complex component or circuit into a simple form to make analysis. 

The equivalent circuit built up using these procedures, and make the circuit for analysis of the working characteristics at every level of operation and attain almost the non-linear and linear behavior of the original component or circuit.


Equivalent circuits of diode

Before considering the equivalent circuit of the diode, we need to know about the characteristics of the diode. On the theory of diode we study forward-biased characteristics and reverse biased characteristics, but this not enough at the equivalent circuit, because qualities like the current, voltage, and resistance will not be covered using reverse and forward characteristics.


cutoff region diode equivalent circuit 


diode equivalent circuit 
diode equivalent circuit


At the diode equivalent circuit, we start analyzing from the starting stage, which is at the initial step diode start working with voltage barrier and resistance.


The representation of the first stage is known as piece-wise mode, the circuit consists of a battery and resistor.

The V voltage represents the cutoff voltage of the diode, this may them for every semiconductor material, for silicon the value is 0.7v, and for germanium, it is 0.6v.

The resistance R is always there at diode against the flow of current.

But the forward resistance potential and voltage potential against the operation of the diode is lesser than the reverse bias condition.


Graphical representation 

diode equivalent circuit Graphical representation
diode equivalent circuit Graphical representation


At the graph, X-axis represents the voltage and the Y-axis is current, the graph shows a gap before the increase of voltage and current, this gap is due to the presence of voltage and resistance.

So a slop curve is a spot at the graph, due to the battery and resistor at the equivalent circuit of the diode. 


At Real diode 

This circuit is the best way of representing the diode depletion region which had an internal resistance and material voltage opposition. 


Voltage-current linear region or Active region diode equivalent circuit 

Active region diode equivalent circuit
Active region diode equivalent circuit


This diode equivalent circuit is called constant voltage drop or simplified equivalent circuit, the circuit consists of the direction of current representation and battery for voltage.


Graphical representation of the voltage-current linear region 

Graphical representation of the voltage-current linear region
Graphical representation of the voltage-current linear region

In this circuit we don’t have the presence of resistance at the circuit, so a linear increase in voltage and current value at this stage, which means after the starting of the circuit, a linear increase in current and voltage value is shown in the graph.


At real diode 

This equivalent circuit of the diode is the perfect example for diode after reaches the active region, here the diode didn’t experience any resistance, a linear increase in current, and the voltage value is shown at this stage.

But the presence of internal resistance at the semiconductor diode can’t be removed, because every material has its resistance. 


Ideal model diode equivalent circuit

Ideal diode equivalent circuit
Ideal diode equivalent circuit


This diode equivalent circuit shows the ideal condition of the diode, which means this ideal model circuit didn’t have voltage potential that is battery and resistor.


At real diode 

The opposing qualities like voltage potential and resistance potential are not present, but this is not possible in a practical situation, every conducting and semiconductor material has a minute resistance and potential differences across it.


Graphical representation of ideal diode 

Graphical representation of ideal diode
Graphical representation of ideal diode


The graphical representation of the ideal model is an interesting one because the presence of resistance and voltage is not at this equivalent model. So the power given into the circuit and increase of energy on the diode is at the same time.


 Forward biased and Reverse biased 


Forward biased  


At forward biased condition equivalent circuit almost looks like an approximate model, that which having potential differences and resistance at initial stages.

And after the initial representation, the working switch over to the next level that we represent with the ON switch.

But the reverse-biased diode equivalent circuit is much simple, that we represent it with an OFF switch or open switch.

Reverse biased
Reverse biased


In real life, the diode forward biased condition is almost the same as the piece-wise model, that having voltage and resistance quantities, but after the cutoff voltage they reach active condition. 

The reverse-biased condition of the real diode is not the same as the open switch, but also they include reverse-biased cutoff region and active region on reverse condition, the real life application of reverse biased active condition is been utilize by Zener diode. 

la4440 amplifier circuit pcb layout


The theory behind the equivalent circuit network is simple, just make a model for a circuit or an active component, using a passive component.

At the making of the model circuit, we need to consider the voltage, current, and resistance values.

And after the making, analyze the characteristics and behavior of the circuit and make an approximate value using an equivalent circuit and merge the values towards the real circuit or component.

In this article, we recreate the characteristics and behaviors of a diode using three models such as piece-wise linear equivalent circuit, constant voltage drop or simplified equivalent circuit, and ideal equivalent circuit.

These diode equivalent circuits start working from piece-wise model to ideal model that means, removing resistance first and then remove voltage difference, this will make a simplified or ideal version of the diode. 

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