Introduccion al diodo

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Electro - Principles I
The PN Junction Diode Introduction to the PN Junction Diode

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ETEC 1 120

Note: In this chapter we consider conventional current flow. The schematic symbol for the pn junction diode the shown in Figure 1. The n-type material is called cathode and the p-type Anode (A) Cathode (C) material is called the anode. p-type n-type Note that the schematic symbollooks like an arrow head. The arrow head points in the direction of conventional current flow. A diode conducts when the following conditions are met: 1) The arrow points to the more negative of the diode potentials; that is, the cathode is more negative than the anode. 2) The difference of potential across the diode (from lead to lead) exceeds the barrier potential of the device: 0.7 volts forsilicon diode and 0.3 volts for germanium diode. Examine figure 2.2 in the text on page 24. Note that each diode symbol points to the more negative potential. Note that in each case conventional current flow will be in the direction of the arrow. A pn- junction diode is reverse biased when the n-type material is more positive p-type material. It will not conduct when the arrow points to the morepositive of the diode potentials. Examine figure 2.3 in the text on page 25. Note that each diode symbol points to the more positive potential therefore each diode is reverse biased.
Fig. 1

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ETEC 1 120

Electro - Principles I
The PN Junction Diode

Diode Models There are three models of the diode that we need to consider. A model is a representation of a component or circuit thatdemonstrates one or more of the characteristics of that component or circuit. The first model is the ideal diode model. This is the simplest model in which the diode is a simple switch that is either closed (conducting) or open (non conducting). This model is used only in the initial stages of troubleshooting where we are considering only a go or no go situation. The second model is the practicaldiode model. It is a bit more complex than the ideal diode model. The practical diode model includes the diode characteristics that are considered when mathematically analysing a diode circuit and when determining whether or not a given diode can be used in a given circuit. The third model is called the complete diode model. It is the most accurate of the diode models. It includes the diodecharacteristics that are considered only under specific conditions such as in circuit development (or engineering) or high frequency analysis.

Electro - Principles I
The Ideal Diode Model
The Ideal Diode

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ETEC 1 120



When Forward Biased
- The diode will have no resistance - The diode will have no control over the current through it. - The diode will have no voltagedrop across its terminals.

Forward Operating Region

Forward Bias


When Reverse Biased
- The diode will have infinite resistance - The diode will not pass current. - The diode will drop the entire voltage across its terminals.

Reverse Operating Region

VK = 0 V

Reverse Bias

The Ideal Diode acts like a Switch

Figure 2


The graph in Figure 2 illustrates thecharacteristics of the ideal diode model. Diode forward voltage (VF) and reverse voltage (VR) are measured along positive and negative x-axes. Quadrant I of the graph is labelled as the forward operating region because every combination of (VF) and (IF) fall within this region of the graph. Quadrant III of the graph is labelled as the reverse operating region. Here the diode is reverse biased andnegative values of voltage (VR) are being applied to it. Notice that as the reverse voltage (VR) increases, the reverse current (IR) remains at zero. This implies that the reverse biased diode is acting like an open switch, since there is no current through the device, regardless of the applied voltage. Work through example 2.1 & 2.2 in the text.

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