Lesson Notes By Weeks and Term v4 - SHS 1
ELECTRONIC DEVICES AND CIRCUITS
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ELECTRONIC DEVICES AND CIRCUITS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Applied Technology
Class: SHS 1
Term: 2nd Term
Week: 4
Grade code: 1.3.2.LI.2
Strand code: 3
Sub-strand code: 2
Content standard code: 1.3.2.CS.1
Indicator code: 1.3.2.LI.2
Theme: ELECTRICAL AND ELECTRONIC TECHNOLOGY
Subtheme: ELECTRONIC DEVICES AND CIRCUITS
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This lesson introduces one of the most fundamental electronic components: the diode. We will explore what diodes are, how they are made, and their function as the "one-way streets" for electric current. Understanding diodes is crucial because they are found in almost every electronic device we use daily in Ghana – from the charger for your mobile phone and the remote control for your television, to the solar panel systems powering homes and traffic lights in our cities. By the end of this lesson, you will understand the magic that allows us to convert the AC power from the Electricity Company of Ghana (ECG) into the DC power our gadgets need.
This section covers the core knowledge required to understand diodes. We will build our knowledge step-by-step. A. The Foundation: The P-N Junction
The heart of every diode is the P-N Junction. To understand this, we must first look at semiconductors. Semiconductors: These are materials like Silicon (Si) and Germanium (Ge) that are not good conductors like copper, nor good insulators like rubber. Their conductivity can be precisely controlled. Doping: This is the process of adding a small, controlled amount of impurity to a pure semiconductor to change its electrical properties. N-Type Semiconductor: Pure silicon is doped with an element that has five valence electrons (e.g., Phosphorus). This introduces extra "free" electrons, which are negative charge carriers. Think of 'N' for Negative. P-Type Semiconductor: Pure silicon is doped with an element that has three valence electrons (e.g., Boron). This creates "holes" – empty spots where an electron should be. These holes act as positive charge carriers. Think of 'P' for Positive. Formation of the P-N Junction: A P-N junction is formed when a piece of P-type semiconductor material is joined to a piece of N-type semiconductor material. Diffusion: Immediately after joining, the free electrons from the N-side are attracted to the holes on the P-side. They diffuse (move) across the junction to combine with the holes. Formation of the Depletion Region: As electrons leave the N-side, they leave behind positive ions. When they fill holes on the P-side, they create negative ions. This creates a thin layer at the junction that is empty of free charge carriers (electrons or holes). This region is called the Depletion Region or Depletion Layer. Barrier Potential: The buildup of positive ions on the N-side and negative ions on the P-side creates an electric field across the junction. This field opposes any further diffusion of charge carriers. The voltage created by this field is called the barrier potential. For silicon, this is approximately 0.7 Volts. B. Biasing the Diode: Making it Work
"Biasing" means applying an external voltage to the P-N junction. There are two ways to do this: Forward Bias (The "On" State): Connection: The positive terminal of a DC power source is connected to the P-type side, and the negative terminal is connected to the N-type side. Operation: The applied positive voltage pushes the holes in the P-region towards the junction, and the negative voltage pushes the electrons in the N-region towards the junction. This force is strong enough to overcome the barrier potential (0.7V for Si). The depletion region shrinks and effectively disappears, allowing current to flow easily through the diode. Analogy: This is like pushing a door open in the correct direction. A small push (0.7V) is needed to get it to unlatch, and then it swings open easily. Reverse Bias (The "Off" State): Connection: The negative terminal of the DC power source is connected to the P-type side, and the positive terminal is connected to the N-type side. Operation: The applied positive voltage pulls the electrons in the N-region away from the junction, and the negative voltage pulls the holes in the P-region away from the junction. This causes the depletion region to become much wider, strengthening the barrier. No significant current can flow. (Only a very tiny "leakage current" passes). Analogy: This is like pushing a door on its hinged side. No matter how hard you push, it won't open. It remains closed, blocking the way. C. Types of Diodes, Their Construction, and Applications
While all diodes are based on the P-N junction, they are constructed differently for special purposes.