In this article I have discussed in detail what is the diode ideal and practical model. How do we treat the diode as a circuit element. Which diode model is best while analyzing or designing a circuit. Basically diode is a pn junction device and we can analyze any circuit in three possible ways when that circuit contains a diode in it.
There are three models of the diode:
- Ideal model
- Practical model
- Complete diode model
what is the diode ideal model?
This is the most simple approach where we treat the diode as an ideal element. By ideal we mean, we will ignore the barrier potential of the diode that is 0.7v in case of silicon and 0.3 v in case of germanium when it is forward biased. So, when diode is forward biased, we will say infinite amount of current is flowing with zero voltage drop across its terminals. When it is reverse biased, we will say it has infinite resistance and hence zero leakage current across its terminal.
The ideal diode model is not much accurate model and can be modeled as a simple switch.
In this model we have ignored barrier potential, forward dynamic resistance and reverse leakage resistance. This model is helpful for troubleshooting or while checking diode is working or not properly. We get the following equations in this case
What is the diode practical model?
In this model barrier potential is included. When diode is forwarded biased it is considered as a closed switch with a voltage source connected in series. This voltage source is actually a barrier potential that must be exceeded by the external battery in order to cause the conduction. When diode is reverse biased it is equivalent to an open switch just like in case of ideal diode model. The barrier potential has no effect on reverse bias.
The calculations can be done using the following formulas
What is the complete diode model?
As its name indicates, all the parameters that we neglected in ideal model are now considered. So when diode is forward biased, a voltage source of 0.7v and a small dynamic resistance connected in series is considered with external biased voltages. While in reverse bias condition it is again an open switch but with a large reverse resistance connected in parallel with a switch. This resistance provides path to the leakage current that is present always. This is the most accurate approximation of the diode as it considers all parameters of it during analysis.
The trademark bend for the total diode model is appeared in Figure (c). Since the boundary potential and the forward powerful obstruction are incorporated, the diode is expected to have a voltage across it when forward-one-sided. This voltage (VF) comprises of the boundary expected voltage in addition to the little voltage drop across the dynamic opposition, as demonstrated by the segment of the bend to one side of the inception. The bend inclines on the grounds that the voltage drop because of dynamic obstruction increments as the current increments. For the total model of a silicon diode, the accompanying equations apply:
The converse current is considered with the equal obstruction and is shown by the bit of the bend to one side of the source. The breakdown segment of the bend isn’t indicated on the grounds that breakdown is certainly not a typical method of activity for most diodes. For investigating work, it is pointless to utilize the total model, as it includes confounded figuring’s. This model is for the most part fit to plan issues utilizing a PC for recreation. The ideal and useful models are utilized for circuits in this content, aside from in the accompanying model, which represents the distinctions in the three models.
which diode model is better for a circuit? Ideal, practical or complete?
If we are generally solving a numerical problem then it is preferable to use an ideal diode model where the voltages dropped across a diode are not of significance importance. For example while designing an inverter or a switch. While working in your college laboratory it is better to use a practical model of diode. Where you will consider 0.7V voltage drop across a diode. Complete diode model is used when you are analyzing a simple circuit or when a circuit is not much complex. Since it would be easier to consider the effect of dynamic resistance and reverse resistance as well.
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