Lesson Notes By Weeks and Term v4 - SHS 1
ELECTRONIC DEVICES AND CIRCUITS
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ELECTRONIC DEVICES AND CIRCUITS
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Subject: Applied Technology
Class: SHS 1
Term: 2nd Term
Week: 3
Grade code: 1.3.2.LI.3
Strand code: 3
Sub-strand code: 2
Content standard code: 1.3.2.CS.1
Indicator code: 1.3.2.LI.3
Theme: ELECTRICAL AND ELECTRONIC TECHNOLOGY
Subtheme: ELECTRONIC DEVICES AND CIRCUITS
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Welcome, learners! Look around you. Your mobile phone charger, the power adapter for your laptop or television, and even the system that charges a car battery all perform a magical task: they change the alternating current (AC) from the ECG mains socket into the direct current (DC) that our gadgets need. The small, essential component at the heart of this process is the diode. In this series of lessons, we will explore the diode, which acts as a one-way gate for electricity. We will learn how to test them, how to use them to build fundamental circuits like rectifiers, and how to apply them in practical projects like a simple security alarm.
2.1 What is a Diode?
A diode is an electronic component that allows electric current to flow in only one direction. Think of it like a one-way street or a valve in a water pipe that only lets water flow forward. Symbol: The arrow in the symbol points in the direction of conventional current flow. Terminals: Anode (A): The positive terminal. Current enters here. Cathode (K): The negative terminal. Current exits here. The physical diode usually has a silver or white band to indicate the cathode side. 2.2 How a Diode Works: Forward and Reverse Bias Forward Bias: When you connect the positive terminal of a power source to the anode and the negative terminal to the cathode, the diode is "forward-biased." It acts like a closed switch and allows current to flow through it. A small voltage (about 0.7V for silicon diodes) is dropped across the diode. Reverse Bias: When you connect the positive terminal of the power source to the cathode and the negative to the anode, the diode is "reverse-biased." It acts like an open switch and blocks the flow of current. 2.3 How to Test a Diode with a Digital Multimeter (DMM)
This is a crucial skill for any electronics technician. We must exhibit honesty in reporting our findings.
Procedure: Set the Multimeter: Turn the dial on your DMM to the diode test symbol (it looks like the diode symbol). This mode sends a small current through the component to test it. Forward Bias Test: Connect the red (positive) probe of the multimeter to the anode of the diode. Connect the black (negative) probe to the cathode (the side with the band). Expected Result (Good Diode): The multimeter will display a small voltage reading, typically between 0.5V and 0.8V for a silicon diode. Reverse Bias Test: Swap the probes. Connect the red (positive) probe to the cathode. Connect the black (negative) probe to the anode. Expected Result (Good Diode): The multimeter will display "OL" (Open Loop), "1", or a very high resistance, indicating that no current is flowing.