What is an ideal diode?

Introduction

An ideal diode functions as a theoretical electronic device that allows current to flow in only one direction without any voltage drop during conduction and presents infinite resistance when reverse-biased. Engineers often use this concept in circuit analysis to simplify calculations and set a benchmark for comparing the behavior of real-world diodes in practical applications.

Diagram of an ideal diode with a triangle and line symbol, labeled "+" and "-", on a peach gradient background. Text reads "IDEAL DIODE".

What is an ideal diode?

Diodes are essential in controlling electrical current in electronic devices, with the ideal diode serving as a useful theoretical model for simplifying diode behavior analysis and circuit design.

The first electronic device to be introduced is called the diode. It is the simplest of semiconductor devices but plays a very vital role in electronic systems, having characteristics that closely match those of a simple switch. It will appear in a range of applications, extending from the simple to the very complex.

We will also cover important data and graphs found on specification sheets, along with construction details and characteristics. This will help you understand the terminology manufacturers use and show the wealth of information they typically provide.

The term ideal will be used frequently in this text as new devices are introduced.It refers to any device or system that has ideal characteristics perfect in every way.It provides a basis for comparison, and it reveals where improvements can still be made. The ideal diode is a two-terminal device having the symbol and characteristics shown in Fig 1 and 2, respectively.

Diagram of a diode with an arrow pointing right, signifying current flow (Id). Plus and minus signs indicate voltage (Vd) across the diode.

Figure 1

Graph of diode characteristics; vertical axis is current (Id) and horizontal is voltage (Vd). Diode symbols show current flow direction.

Figure 2

Ideally, a diode will conduct current in the direction defined by the arrow in the symbol and act like an open circuit to any attempt to establish current in the opposite direction. In essence.

The characteristics of an ideal diode are those of a switch that can conduct current in only one direction.

The following descriptions will define all letter symbols, voltage polarities, and current directions. When the applied voltage polarity matches the one shown in Fig. 1, you should examine the portion of the characteristics shown to the right of the vertical axis in Fig. 2.

If a reverse voltage is applied, the characteristics to the left are pertinent. If the current through the diode has the direction indicated in Fig 1, the portion of the characteristics to be considered is above the horizontal axis, while a reversal in direction would require the use of the characteristics below the axis. For the majority of the device characteristics that appear in this book, the ordinate (or “y” axis) will be the current axis,while the abscissa (or “x” axis) will be the voltage axis.

One of the important parameters for the diode is the resistance at the point or region of operation. If we consider the conduction region defined by the direction of `I_D` and polarity of `V_D` in Fig 1 (upper-right quadrant of Fig 2), we will find that the value of the forward resistance,`R_F`, as defined by Ohm’s law is

`R_F=frac{V_F}{I_F}=frac{O;V}{2,3,mA,...,oranypositivevalue}=0`

Ω (short circuit)

where `V_F` is the forward voltage across the diode and `I_F` is the forward current through the diode.

The ideal diode, therefore, is a short circuit for the region of conduction.

Consider the region of negatively applied potential (third quadrant) of Fig 2,

`R_R=frac{V_R}{I_R}=frac{-5,-20,or any reverse bias potential}{0mA}=∞`

Ω (open-circuit)

where `V_R` is reverse voltage across the diode and `I_R` is reverse current in the diode.The ideal diode, therefore, is an open circuit in the region of nonconduction.In review, the conditions depicted in Fig 3 are applicable.

Diagram showing diode circuits; the top circuit is forward-biased with a short circuit, and the bottom is reverse-biased with an open circuit. Graph relates current (I_D) to voltage (V_D).

Figure 3

Diagram showing diode operation: Top row, forward-bias with current flow; bottom row, reverse-bias with no current flow. Arrows indicate direction.

Figure 4

To determine if a diode is conducting, check the direction of current $IDI_D$ from the applied voltage. If the current flows in the same direction as the diode symbol’s arrowhead, the diode conducts (Fig. 4). If the current flows opposite, the diode is non-conducting and acts like an open circuit (Fig. 4).

As indicated earlier, the primary purpose of this section is to introduce the characteristics of an ideal device for comparison with the characteristics of the commercial variety. As we progress through the next few sections, keep the following questions in mind:

1.How close will the forward or “on” resistance of a practical diode compare with the desired 0-Ω level?

Ans=The forward or "on" resistance of a practical diode is not zero ohms; it is typically small but nonzero. In real-world diodes, the forward resistance can range from a few tenths of an ohm to a few ohms, depending on the type of diode and its specifications.

2.Is the reverse-bias resistance sufficiently large to permit an open-circuit approximation?

Ans=Yes, the reverse-bias resistance of a diode is typically very large, often in the megaohm to gigaohm range, making it effectively an open circuit in reverse bias conditions.

Conclusion

The perfect diode serves as an essential tool for analyzing and designing electronic circuits. Although it simplifies calculations and facilitates understanding of basic principles, actual diodes exhibit constraints that affect their performance. Therefore, engineers and researchers use ideal diode models as a foundation. Moreover, they incorporate practical diode traits to develop reliable and effective electronic systems.

What is an ideal diode?

Introduction

What is an ideal diode?

Conclusion

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