At the end of this module, you should be able to:
• Describe what a junction diode is and how it is made.
• Define depletion region and barrier voltage.
• Explain the difference between forward bias and reverse bias of a diode.
• Draw and label the schematic symbol for a diode.
• Describe three diode construction techniques.
• Identify the most common diode packages.
• Test diodes using an ohmmeter.
Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some
tips for you:
1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.
2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.
3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.
4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.
5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.
One of the most basic and useful electronic components is the PN-junction diode.
A junction diode is created by joining Ntype and P-type materials together.
The region near the junction is referred to as the depletion region. Electrons cross the junction from the N-type to the P-type material and thus both the holes and the electrons near the junction are depleted.
The size of the depletion region is limited by the charge on each side of the junction.
The charge at the junction creates a voltage called the barrier voltage.
The barrier voltage is 0.3 V for germanium and 0.7 V for silicon.
A current flows through a diode only when the external voltage is greater than the barrier voltage.
Forward bias forces the majority carriers to the junction and collapses the depletion region. The diode conducts.
A diode that is forward biased conducts current. The P-type material is connected to the positive terminal, and the N-type material is connected to the negative terminal.
Reverse bias widens the depletion region. The diode does not conduct.
Reverse bias forces the minority carriers to the junction. This causes a small leakage current to flow.
A diode is a one-directional device.
A diode’s maximum forward current and reverse voltage are specified by the manufacturer.
Diode leads are identified as the cathode lead and the anode lead.
In a diode, the cathode is the N-type material, and the anode is the P-type material
Diodes can be constructed by the grown junction, alloyed junction, or diffused junction method.
The diffused junction method is the one most often used.
Packages for diodes of less than 3 A identify the cathode end of the diode with a black, white or silver band.
A diode is tested by comparing the forward to the reverse resistance with an ohmmeter.
When a diode is forward biased, the resistance is low.
When a diode is reverse biased, the resistance is high.
A diode used to change alternating current to direct current is called a rectifier diode.
Schottky diodes do not have a depletion region and turn off much faster than silicon diodes.
A diode used to stabilize or regulate voltage is the zener diode.
