Semiconductor Diode
Basic definition: A semiconductor diode is a small electronic component that controls the direction of current flow. It is specially made so that electric current can move through it in only one direction, just like a one-way street for electricity.
One-way current flow: This means that the diode allows electricity to pass through easily in one direction (called the forward direction), but if the current tries to go the other way (the reverse direction), the diode blocks it like a closed gate.
Structure
Material composition: A diode is built by putting together two different types of materials called semiconductors. These materials are called p-type and n-type, and they are joined to form what’s called a p-n junction.
p-type semiconductor: The p-type material is made by adding a tiny amount of another element, like boron, into pure silicon. This process is called doping. The boron creates empty spaces or “holes” that act like spots where electrons are missing. These holes act like positive charges that can move.
p-type carriers: In the p-type material, these holes are the main carriers of electric charge. They behave as if positive particles are moving around.
n-type semiconductor: The n-type material is made by adding a different element, such as arsenic, into silicon. This also is done by doping. The extra electrons from arsenic are free to move, which means they can carry electricity.
n-type carriers: In the n-type material, these free-moving electrons are the main carriers of charge. They act like tiny negatively charged particles flowing through the material.
p-n junction: The place where the p-type and n-type materials meet inside the diode is called the p-n junction. This area plays a very important role in controlling how the diode works.
Terminals: A diode has two ends or terminals. One end is called the anode, which is connected to the p-type material, and the other end is the cathode, connected to the n-type material. These terminals help connect the diode into a circuit.
Diode Bias
Bias definition: The word “bias” in electronics means how we connect a voltage across the diode. This voltage direction affects whether the diode lets current through or not.
Forward Bias
Connection in forward bias: In forward bias, the battery’s positive end is connected to the diode’s anode (p-type side), and the negative end to the cathode (n-type side). This setup allows current to flow.
Depletion layer narrowing: There is a small area between the p-type and n-type called the depletion layer. In forward bias, this layer becomes thinner, making it easier for current to pass through the diode.
Current flow mechanism: In this state, the free electrons from the n-type material move across the junction and fill the holes in the p-type material. This movement of charges creates a flow of electric current.
Resistance state: When forward biased, the diode has very low resistance, meaning it does not stop the current much, so electricity flows easily.
Reverse Bias
Connection in reverse bias: In reverse bias, the battery is connected the opposite way—the negative terminal goes to the anode, and the positive to the cathode. This setup tries to push charges away from the junction.
Depletion layer widening: In this setup, the depletion layer gets wider, which makes it very difficult for any current to flow through the diode.
Charge carrier movement: Electrons and holes are pulled away from the p-n junction, so they cannot meet and allow current to flow. This increases resistance in the diode.
Resistance state: In reverse bias, the diode acts like an insulator. It has very high resistance and stops almost all current from flowing through it.
Uses of Diodes
Primary application: One of the most common uses of diodes is to change alternating current (AC) into direct current (DC). This is done using a special circuit called a rectifier.
Rectification
Definition of rectification: Rectification is the process of turning AC, which changes direction all the time, into DC, which flows in only one direction.
Diode role in rectification: Diodes are perfect for this job because they only let current go one way, blocking the other direction. This makes them essential in rectifier circuits.
Half-wave Rectification
Basic operation: In a half-wave rectifier, we use just one diode. It only allows one half (the positive half) of the AC signal to pass through, and blocks the other half.
Positive cycle: When the AC voltage is in its positive half-cycle, the diode turns on and lets current flow to the output.
Negative cycle: When the AC voltage goes into its negative half-cycle, the diode turns off and blocks the current. This makes the output look like bumpy or pulsating DC.
Full-wave Rectification
Bridge configuration: In full-wave rectification, we use four diodes in a bridge arrangement. This clever setup lets both halves of the AC signal be used.
Output quality: Because both halves of the AC signal are turned into current that flows in the same direction, the result is a much smoother and more continuous DC.
Diode behavior in cycles: During the positive half-cycle, two of the four diodes conduct (allow current through), while the other two block it. During the negative half-cycle, the roles switch, and the other two diodes conduct instead.
Smoothing
Purpose of capacitor: After rectification, the current is still a bit bumpy. A capacitor is added to help smooth out the voltage and make it more steady.
Charge storage: The capacitor works by storing electric charge when the voltage is high, and then releasing it when the voltage drops. This keeps the voltage from going up and down too much.
Stabilization effect: Because the capacitor fills in the dips and cuts the peaks, the result is a more constant and stable DC output, which is better for powering electronic devices.