How Diodes, Resistors, Transistors Work + Diagrams

[an error occurred while processing this directive] Diodes, Resistors, and Transistors
This is kinda cool, has diagrams and how PN junctions work (the heart of diodes), resistors, transistors, etc..

Semi-Conductors	P-N Junctions
Atom Structure	Diodes
Covalent Bonding	Transistors
Electron Flow in Semi-Conductors	Resistors
Ions	Capacitors
Electron-Hole Theory

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Semi-Conductors
Ok, before jumping into diodes, I will have to explain how diodes work.
Most use a manufacturing process that creates a "P-N Junction".
Before I can explain how a P-N Junction works, I'll have to start out with the basics...
How Semi-Conductors work.

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Simple Atom Structure
I'm assuming you know what an atom is, so I will just jump in.
An atom is made of 3 parts:

Proton - Positivly Charged - Located in nucleus
Neuton - Neutral (no charge) - Located in nucleus
Electron - Negativly Charged - Orbits around nucleus

A neutrally charged atom has the same number of protons and electrons.
Neutrons don't matter here since they have no charge, all they do is add weight.

The electrons orbit in rings (planes) around the nucleus, but there's a certain number per ring...
Starting from nucleus out, here's how many electrons per ring:

1st ring - 2 Electrons
2nd ring - 8 Electrons
3rd ring - 18 Electrons
4th ring - 32 Electrons

If say there were 14 Electrons (like in the Silicon atom), the rings would be like this:

1st ring - 2 Electrons
2nd ring - 8 Electrons
3rd ring - 4 Electrons

The outermost ring (3rd on Silicon) is called the "Valence Ring".
The Valence ring is the only ring that can shed or gain electrons.

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Covalent Bonding is when there is a cluster (crystal structure) of atoms where the electrons can bond with other electrons (creating a lattice type crystal structure).
In the case of Silicon and Germanium, there are 4 electrons in the Valence ring.
This allows them to bond exactly (8 electrons) with other Silicon or Germanium atoms.
The valence electrons don't move about easily like this.

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Electron flow in Semi-Conductors. At room temperature or lower, semiconductor electrons do not flow easily, so they are insulators. Above room temperature, the electrons start to flow, and it becomes a conductor.

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Ions. When an electron leaves an atom, that atom that was neutral now becomes a positivly charged ion. When an electron arrives at an atom, the atom becomes a negativly charged ion. If the whole structure is a semi-conductor, the whole thing is still neutral due to equal number of protons and neutrons.

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Electron-Hole Theory. It used to be thought that charges moved from positive (+) to negative (-), which is known as Conventional Current Flow. It is now known that it is opposite of that and current flow is from negative (-) to positive (+), known as Electron Flow.
The Electron-Hole Theory is that when an electron leaves an atom (making a positive ion), it creates a hole which another electron can fill, which makes the atom where that electron just left a positive ion, which another electron fills to try to keep everything neutral. So if you get it, current flow is from - to +.

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P-N Junctions
Ok, still have a few more things to explain, so hang on...

Doping is intentionally adding impurities. It makes semi-conductors either P (positive, +) or N (negative, -).

Semi-Conductors doped with either P or N-Type impurities are known as Extrinsic Semi-Conductors.

Remember that semi-conductors have 4 valence electrons, and remember the magic number is 8...

Atoms with 4 Valence electrons (Semi-Conductors) are known as Tetravalent atoms.

Donor Atoms have 5 valence electrons and create N-type when a semi-conductor is doped with it.

N-Type atoms are known as Pentavalent impurities.
Examples: Arsenic, Antimony, Bismuth, and Phosphorus
N-Type atoms when doped into a semi-conductor have extra electrons and make the crystal Negative.

Acceptor Atoms have 3 valence electrons and create P-type when a semi-conductor is doped with it.

P-Type atoms are known as Trivalent impurities.
Examples: Aluminum, Indium, Gallium, and Boron
P-Type atoms when doped into a semi-conductor leave holes and make the whole crystal Positive.

When you join a P-Type material with an N-Type material, you have created a P-N Junction.
Since N-Type can donate and P-Type can accept electrons, they combine and make a Junction Field.
The outer parts still have extra (N-Type side) and missing (P-Type side) electrons.

By placing an electric charge at the N-Type side, the Junction Field remains small and current will cause the electrons on the N-type side to cross over to the P-Type side and out the P-N Junction.
If you reverse the connections and place a charge on the P-Type side (hook the - side of the power source to the P-Type side), the Junction Field will grow larger and not allow current to flow. This is the operating principle of a Diode.

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Diodes
Jump To: General Purpose Zener Diodes SCR's

A Diode is a device that allows current to flow in one direction only.

A Diode is also known as a Rectifier

A diode is simply a P-N Junction (just like above, just add leads), but has a LOT more atoms than pictured.

The Cathode is the P-Type side, Anode is the N-Type.
When current is applied to the Cathode side, the Junction Field remains small and allows the current to flow. Switch and place current on the Anode side, the Junction Field will grow larger and not allow current to flow.

The electrical symbol for a diode is an arrow pointing away from the current flow (reason: the symbol was designed back when conventional current flow was still around) at a line. You could say the line is where current flowing in the direction of the arrow is blocked.

Diodes come 3 ways: General Purpose (above), Zener Diode, and Silicon Controlled Rectifier (SCR).

General Purpose diodes allow current to flow in a single direction.

Forward biased have current to cathode, Junction Field gets smaller, current flows.
Reverse biased have current to anode, Junction Field gets larger, current flow stops.

Zener Diodes are manufactured so reverse biased breakdown voltage can be controlled to a limit.

Biasing allows Zener Diode to have current applied to Anode; Junction Field will get bigger, but only to a point, which will allow voltage leakage of whatever the manufacturer set it at.
Works like G.P. diode when current applied to Cathode.
Used as voltage regulators, voltage dividers, and voltage limiter circuits.

Silicon Controlled Rectifiers (SCR's) work just like G.P. diodes, but have a gate to initiate flow.

Has 3 leads: Cathode, Anode, and Gate.
No current will flow, either direction, until control voltage is applied to Gate.
Once flow has started (Cathode to Anode), will continue even after control voltage at Gate disappears.
Used in rectification circuits (AC to DC, like in a computer power supply).
Also in Motor Controls (3 SCR's replace Magnetic Starter).

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Transistors
Jump To: UJT's J-FET's BJT's

Transistors are made from different arrangements/combonations of P-N Junctions.

Like an SCR, power applied to 1 terminal controls current flow through the other 2 terminals.
Unlike an SCR, Transistors require constant current on this control terminal.
Transistors can also control current, where as an SCR can only turn it on or off.

Unijunction Transistors (UJT's) are specialized transistors.

When control current is applied to Emitter, controlled pulses flow between Base1 and Base2.

Junction Field Effect Transistors (J-FET's) are used as a voltage controlled current source.

J-FET's are either n-channel or p-channel, which is the polarity applied.
J-FET's have 3 terminals: Drain (D), Source (S), and Gate (G).
n-channel JFET's need negative (-) voltage at Gate to operate.
p-channel JFET's need positive (+) voltage at Gate to operate.
J-FET's can be made by other processes than P-N junctions.
Example: by using a metal-oxide semi-conductor process, name changes to
Metal-Oxide Semi-Conductor Field Effect Transistor (MOSFET).

MOSFET's are commonly found in audio amplifiers.

I'm taking an educated guess that low level voltage pulses (like ~4-5V RCA output from head unit) are applied to Gate, then higher current is placed on Source, and Drain is the output to the speakers.

Bipolar Junction Transistors (BJT's) are the most common. Used as current controlled current source.

Have Base (B), Collector (C), and Emitter (E).
I_CE indicates current flow (I) through Collector (C) and Emitter (E).
I_BE indicates current flow (I) through Base (B) and Emitter (E).
B-E path is forward-biased (current may flow), and C-B path is reverse-biased (no current flow).
When BJT's are used as amplifiers, I_C will be a multiple of I_B.

This multiple is called GAIN and specified as h_FE.
Example: A transistor with h_FE=20 means that I_C=20xI_B.

Current through Emitter (E) is the sum of I_C+I_B.

This is why a small current through B-E path can control a larger current through C-E path.
Gain (h_FE) varies. Low Gain makes better high frequencies (tweeters), High Gain makes better low frequencies (subwoofers).

PNP and NPN indicates the process how the BJT was constructed.

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Resistors
Jump To: Fixed Potentiometer Rheostat Color Codes

Resistors are made to oppose current flow. Resistance of is represented in Ohms (Ω).

Fixed Resistors have a set value of resistance (within a tolerance range).

Chemical composition of determines ohmic value. Usually they are a molded composition (Carbon).
Physical size determines Wattage rating (the ability to give off heat.

Carbon resistors change value as they age and have limited power handling.

Variable Resistors are able to change the value of resistance.

A Potentiometer controls voltage by varying resistance. Has 3 terminals.

Varying voltage is available at the terminal with the arrow (see figure), which is movable along the resistor.

A Rheostat controls current by varying resistance. Only has 2 terminals.

The arrow moves along the resistor, and provides varying current at the terminal it's connected to.

This resistor has 27,000Ω (27kΩ) of resistance.

This is calculated by looking at the bands on the resistor body and comparing with the charts below.

1st band is 1st significant digit, in this case RED which means 2.
2nd band is 2nd significant digit, in this case VIOLET which means 7.
3rd band is multiplier, in this case ORANGE which means 1,000.
4th band is tolerance, may or may not be present, here is SILVER or 10%.
5th band is failure rate, may or may not be present, here is GOLD or 0.001%.

You then join the values for Bands 1 and 2 (2 and 7 = 27), then multiply by the mulitplier (27x1,000=27,000).

This resistor is rated at 27,000Ω (27kΩ), has a tolerance of 10% (may vary between 24,300Ω - 29,700Ω).
This particular resistor has a reliability level per 1000 hours, or failure rate, of 0.001%, so very good.

Resistor Color Codes (Bands 1-3)
Color	Significant Figures (Bands 1-2)	Multiplier (Band 3)
Black	0	1
Black
Brown	1	10
brown
Red	2	100
Red
Orange	3	1,000
Orange
Yellow	4	10,000
Yellow
Green	5	100,000
Green
Blue	6	1,000,000
Blue
Violet	7	10,000,000
Violet
Gray	8	100,000,000
Gray
White	9	1,000,000,000
White

Resistor Color Codes (Bands 4 and 5)
Color	Resistance Tolerance (Band 4)	Reliability Level per 1000hrs (Failure Rate - Band 5)
Brown	1%	1%
Brown
Red	2%	0.1%
Red
Orange	3%	0.01%
Orange
Gold	5%	0.001%
Gold
Silver	10%	-
Silver
No Color	20%+	-
-

Capacitors have 2 plates with Di-Electric material between them.

Plates are either soft or hard metal.
Di-Electric material is wax paper, mica, air, oil, glass, or a chemical paste.

Capacitors have 4 states: Charging, Charged, Discharging, and Discharged.
Ability to store charge is determined by size of plates, distance between plates, and dielectric material.
Amount of charge stored is called Capacitance and measured in Farads named after Michael Faraday.

If voltage of capacitor is exceeded, it will punch through the di-electric material and create a short-circuit.

Used in cameras (the high pitched noise after flash), electric fences, computers, etc.

As of Sep 5, 2004, finshed unless I find more to add, which means:
>>>Still under construction<<<

All this was done in Windows

, yay!
Email me at kaneo666@yahoo.com if you would like to use these pictures, thanks.
Last Modified: Monday, 06-Sep-2004 00:14:01 EDT.
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