Diode
Diode
A diode is a 2-terminal semiconductor electronic component conducting current mainly in 1 direction (asymmetric conductance), at low (often zero) voltage and (ideally infinite) resistance in the other.
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Materials
Materials
Diodes most often use silicon as semiconductors externally, via arsenic at its right layer, in n-type parts [1.6] (excess electrons) and gallium at its left layer, in p-type parts [1.7] (excess holes).
[1.9] hole: in diodes and semiconductor physics, the word refers to electron absences in a semiconductor material's a valence band (like silicon or germanium).
Some other semiconductors used in diodes are:
Germanium
Gallium arsenide
Arsenic is an n-type dopant (donors, gives free electrons: − charge carriers) in semiconductors.
Indium phosphide
Gallium nitride
[1.5] Gallium is a p-type dopant (acceptors, makes "holes": + charge carriers) when added to semiconductors like silicon (Si).
[1.1] dopant: small amount of impurity element added to a material (often semiconductors) to alter its electric properties. This controlled introduction of dopants, known as doping, allows for precise control over the conductivity and other characteristics of the material, which is crucial in the production of electronic devices like transistors and diodes.
Properties
Properties
Diodes have a negative, the cathode (K) and positive, the anode (A) terminals.
A diode symbol's line and a real diode's grey/white bar tells it's cathode (negative) terminal, where the current flows toward to.
Diode logic
Diode logic
Diode logic (or diode-resistor logic) makes AND and OR logic gates via diodes and resistors.
Logic gates
Logic gates
Logic gates evaluate Boolean algebra, often via electronic switches controlled by logical inputs connected in parallel or series. Diode logic can only implement OR and AND, as inverters (NOT gates) needs an active device.
If the diodes are non-ideal (e.g., silicon diodes with ~0.7 V drop), the output is slightly less than the highest input (e.g., +9 V → +8.3 V). However, the principle remains the same: the highest forward-biased diode dominates.
E.g. Of these 3 diodes, the 9 V diode is conducting as the diode of the highest anode voltage dominates and set the cathode voltage. Other diodes (+6 V and -4 V) are reverse-biased as their anode voltages are lower than the 9 V cathode voltage.
Forward and reverse bias
Forward and reverse bias
A diode is forward bias (ON) only if it works: It conducts current, from positive to negative or if anode is more positive than cathode by ~0.7V for silicons or ~0.3V for germanium. Conventional current is from anode to cathode.
A diode is reverse bias (OFF) if it won't conduct and acts as an open/anex switch: Current flows from cathode to anode or if cathode (-) is more positive than anode (+).
A diode starts conducting under ~0.7 V, but current becomes significant ~at that point.
Overall, as current goes through a diode, its voltage drop is 0.7 V.
Their electrical properties are varied in many magnitude: 107 Ω-m resistivity (almost an insulator) or as low as 10–6 Ω-m (almost a conductor).
Semiconductors are mainly put as 2 types: n-type (electrons carry current as usual) or p-type (current acts like it's carried by positive charges, the “holes”).
[8] Gallium is the electron receiver and arsenic is the electron donner.
Electrons (conventional current) only flows from positive to negative in a diode
In forward bias, a battery's positive terminal connects to the p-type semiconductor and its negative terminal connects to the n-type semiconductor.
In n-type semiconductors, free electrons are the most charge carriers and holes are the minorities.
In p-type semiconductors, holes are the majority charge carriers and free electrons are the minority charges carriers.
In forward biased real diode, the majority charge carriers carry most of the electric current. The positive charge carriers from p-side to n-side carry the conventional electric current. However, the free electrons from n-side to p-side carry the actual electric current.
When the forward voltage is applied on the real diode, it does not allow the electric current up to a certain voltage because the depletion region present at the p-n junction block the electric current.
Peak inverse voltage
Peak inverse voltage
[1.10] The peak inverse voltage (PIV) or peak reverse voltage (PRV) is the max voltage a diode resists in reverse bias before it breaks. A crucial parameter in diodes, mainly in rectification circuits, as exceeding PIV damages it.
Reverse breakdown is if by using a big negative voltage (cathode to anode) to a diode causes current to flow in reverse, but at times, and it occurs if voltage exceeds a diode's breakdown voltage.
Ideal diode
Ideal diode
An ideal diode is a theoretical diode perfectly conducting current in a direction (forward bias) and blocks it in the other direction (reverse bias), depicted as zero voltage drop if conducting and infinite resistance if blocked--it acts as a perfect switch, either a closed circuit (conducting) or an open circuit (non-conducting), depending on the applied voltage's direction.
Realistic diode
Realistic diode
A realistic diode (unlike ideal diodes that are said to give zero resistance in forward direction and infinite resistance in reverse direction) have resistance and voltage drop even in forward bias, and let some reverse current flow.
True diodes are estimated by piecewise linear models to simplify analysis while accounting for non-idealities like the forward voltage drop and dynamic resistance.
piecewise linear models are represented by many straight line, each valid over a specific input interval
Approximation
Approximation
Behaviors:
Forward bias (VD > 0 or VD = 0) acts as a perfect short circuit
Reverse bias (VD < 0 or ID = 0) acts as a open circuit
Quick Ideal diodes ignores forward voltage drop and leakage current.
Constant voltage drop model
Constant voltage drop model
[10] The constant voltage drop (CVD) model is a simply way to show a diode behaviors in circuits, assuming that if a diode is forward biased (it's conducting), it has a fixed voltage drop across it, often ~0.7 volts for silicon diodes. This simplifies circuit analysis by allowing you to treat the diode as a voltage source of that fixed value. When the diode is reverse biased (not conducting), it's treated as an open circuit.
Forward bias (VD ≥ Vth) is when a diode conducts via a fixed voltage drop: VD ≈ 0.7 (Si) or 0.3 V.
Reverse bias (VD < Vth) is an open circuit (ID = 0)
it's used in most practical DC analyses (e.g., rectifiers, clipping circuits), but it balances simplicity and accuracy.
Types
Types
[1], [8], [9] Many diode types are based on function/structure/application. As some sources list over 20 types, practical circuit design, a smaller subset is commonly used.
a rectifier diode
[2] A rectifier diode converts AC current into DC current, by leeting current to flow in only a direction, filtering out negative half-cycle of AC, done by its unique semiconductor structure: PN junction, letting current to pass when forward-biased and blocks it if reverse-biased.
rectifier: an electric device converting AC current, that periodically reverses direction, to DC, which flows in only a direction.
rectify: correct/adjust/sort out, right
Avalanche diode
References
References
[1] Wikipedia
[1.1] Dopant
[1.2] Semiconductor
[1.3] p–n junction
[1.4] Silicon
[1.5] Gallium
[1.8] Diode modelling
[1.9] Electron hole
[1.10] Peak inverse voltage
[1.11] Diode logic
[2] https://www.indiamart.com/proddetail/12-v-rectifier-diode-12355891612.html
[3] Britannica
[5] Khan Academy
[9] Types of Diodes and Their Applications – 24 Types of Diodes - ELECTRICAL TECHNOLOGY
[11] https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-diodes
[12] G. Tuttle
[13] All About Circuits
[14] Category page - ElectronicsTutorials
[14.1] The Schottky Diode
[15] ELE8922A Electrical Principles II: Homework-diodes and LED's - (Algonquin College) Canva
[16]
Quizzes
Quizzes
[Q1] Flashcards
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