Types of Diodes

Light Emitting Diode (LED): It is one of the most popular type of diodes and when this diode permits the transfer of electric current between the electrodes, light is produced. In most of the diodes, the light (infrared) cannot be seen as they are at frequencies that do not permit visibility. When the diode is switched on or forward biased, the electrons recombine with the holes and release energy in the form of light (electroluminescence). The color of light depends on the energy gap of the semiconductor.


Avalanche Diode: This type of diode operates in the reverse bias, and used avalanche effect for its operation. The avalanche breakdown takes place across the entire PN junction, when the voltage drop is constant and is independent of current. Generally, the avalanche diode is used for photo-detection, wherein high levels of sensitivity can be obtained by the avalanche process.

Laser Diode: This type of diode is different from the LED type, as it produces coherent light. These diodes find their application in DVD and CD drives, laser pointers, etc. Laser diodes are more expensive than LEDs. However, they are cheaper than other forms of laser generators. Moreover, these laser diodes have limited life.

Schottky Diodes: These diodes feature lower forward voltage drop as compared to the ordinary silicon PN junction diodes. The voltage drop may be somewhere between 0.15 and 0.4 volts at low currents, as compared to the 0.6 volts for a silicon diode. In order to achieve this performance, these diodes are constructed differently from normal diodes, with metal to semiconductor contact. Schottky diodes are used in RF applications, rectifier applications and clamping diodes.

Zener diode: This type of diode provides a stable reference voltage, thus is a very useful type and is used in vast quantities. The diode runs in reverse bias, and breaks down on the arrival of a certain voltage. A stable voltage is produced, if the current through the resistor is limited. In power supplies, these diodes are widely used to provide a reference voltage.

Photodiode: Photodiodes are used to detect light and feature wide, transparent junctions. Generally, these diodes operate in reverse bias, wherein even small amounts of current flow, resulting from the light, can be detected with ease. Photodiodes can also be used to generate electricity, used as solar cells and even in photometry.

Varicap Diode or Varactor Diode: This type of diode feature a reverse bias placed upon it, which varies the width of the depletion layer as per the voltage placed across the diode. This diode acts as a capacitor and capacitor plates are formed by the extent of conduction regions and the depletion region as the insulating dielectric. By altering the bias on the diode, the width of the depletion region changes, thereby varying the capacitance.

Rectifier Diode: These diodes are used to rectify alternating power inputs in power supplies. They can rectify current levels that range from an amp upwards. If low voltage drops are required, then Schottky diodes can be used, however, generally these diodes are PN junction diodes.

Small signal or Small current diode - These diodes assumes that the operating point is not affected because the signal is small
· Large signal diodes - The operating point in these diodes get affected as the signal is large.
. Transient voltage supression diodes - This diode is used to protect the electronics that are sensitive against voltage spikes.

· Gold doped diodes - These diodes use gold as the dopant and can operate at signal frequencies even if the forward voltage drop increases.

· Super barrier diodes - These are also called as the rectifier diodes. This diodes have the property of low reverse leakage current as that of normal p-n junction diode and low forward voltage drop as that of Schottky diode with surge handling ability.

· Point contact diodes - The construction of this diode is simpler and are used in analog applications and as a detector in radio receivers. This diode is built of n – type semiconductor and few conducting metals placed to be in contact with the semiconductor. Some metals move from towards the semiconductor to form small region of p- tpye semiconductor near the contact.

· Peltier diodes - This diode is used as heat engine and sensor for thermoelectric cooling.

· Gunn diode - This diode is made of materials like GaAs or InP that exhibit a negative differential resistance region.

· Crystal diode - These are a type of point contact diodes which are also called as Cat’s whisker diode. This didoe comprises of a thin sharpened metal wire which is pressed against the semiconducting crystal. The metal wire is the anode and the semconducting crystal is the cathode. These diodes are obsolete.  

· Avalanche diode - This diode conducts in reverse bias condition where the reverse bias volage applied across the p-n junction creates a wave of ionization leading to the flow of large current. These didoes are designed to breakdown at specific reverse voltage in order to avoid any damage.  

· Silicon controlled rectifier - As the name implies this diode can be controlled or triggered to the ON condition due to the application of small voltage. They belong to the family of Tyristors and is used in various fields of DC motor control, generator field regulation, lighting system control and variable frequency drive . This is three terminal device with anode, cathode and third controled lead or gate.

· Vaccum diodes - This diode is two electrode vacuum tube which can tolerate high inverse voltages.                               

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Introduction to the Diodes

                             A two-terminal semiconductor (rectifying) device, that exhibits a nonlinear current-voltage  characteristics. The function of a diode is to allow current in one direction and to block current in the opposite direction. The terminals of a diode arecalled the anode and cathode. There are two kinds of semiconductor diodes: a P-N junction diode,which forms an electrical barrier at the interface between N- and P-type semiconductor layers, and a Schottky diode, whose barrier is formed between metal and semiconductor regions. But this discussion really ought to start with a bit semiconductors as materials. Semiconductors are crystals that, in their pure state, are resistive (that is, their electrical properties lie between those of conductors and insulators) -- but when the proper impurities are added (this process is called doping) in trace amounts (often measured in parts per billion), display interesting and useful properties.

History of Diode :

                               The oldest ancestor of semiconductor devices was the crystal detector, used in early wireless radios. This device (patented by a German scientist, Ferdinand Braun, in 1899) was made of a single metal wire (fondly called a "cat's whisker") touching against a semiconductor crystal. The result was a "rectifying diode" (so called because it has two terminals), which lets current through easily one way, but hinders flow the other way. By 1930, though, vacuum-tube diodes had all but replaced the smaller but much quirkier crystal detector. The crystal and "cat's whisker" were left to languish as a kids' toy in the form of "crystal radios."

                                  The development of radar during World War II did much to revive the fortunes of crystal detectors (and, as a result, that of semiconductors) -- although temperamental, crystals were better than vacuum-tube diodes at rectifying the high frequencies used by radar. So, during the war, much effort was put into improving the semiconductors, mostly silicon and germanium, used in crystal detectors. At about the same time, Russell Ohl at Bell Laboratories discovered that these materials could be "doped" with small amounts of foreign "impurity" atoms to create interesting new properties.

                       Depending on the selection of impurities (often called dopants) added, semiconductor material of two electricallly-different types can be created -- one that is electron-rich (called N-type, where N stands forNegative), or one that is electron-poor (called P-type, where P stands for Positive). Most of the "magic" of semiconductor devices occurs at the boundary between P-type and N-type semiconductor material -- such a boundary is called a P-N junction. Ohl and his colleagues found that such a P-N junction made an effective diode.

Like many components, diodes have a positive side or leg (a.k.a, their anode), and a negative side (cathode). When the voltage on the anode is higher than on the cathode then current flows through the diode (the resistance is very low). When the voltage is lower on the anode than on the cathode then the current does not flow (the resistance is very high).

An easy way to remember this is to look at the symbol for a diode -- the "arrow" in the diode symbol points the direction in which it allows current (hole flow) to flow.

The cathode of a diode is generally marked with a line next to it (on the diode body). You can see a similar line in the schematic symbols, above.                                                                                                        

How Diodes work?

                                    The diode operates when a voltage signal is applied across its terminals. The application of a DC voltage to make the diode operate in a circuit is called as ‘Biasing’. As already mentioned above the diode resembles to that of a one way switch so it can either be in a state of conduction or in a state of non conduction. The ‘ON’ state of a diode is achieved by ‘Forward biasing’ which means that positive or higher potential is applied to the anode and negative or lower potential is applied at the cathode of the diode. In other words, the ‘ON’ state of diode has the applied current in the same direction of the arrow head. The ‘OFF’ state of a diode is achieved by ‘Reverse biasing’ which means that positive or higher potential is applied to the cathode and negative or lower potential is applied at the anode of the diode. In other words, the ‘OFF’ state of diode has the applied current in the opposite direction of the arrow head. During ‘ON’ state, the practical diode offers a resistance called as the ‘Forward resistance’.  The diode requires a forward bias voltage to switch to the ‘ON’ condition which is called Cut-in-voltage. The diode starts conducting in reverse biased mode when the reverse bias voltage exceeds its limit which is called as the Breakdown voltage. The diode remains in ‘OFF’ state when no voltage is applied across it.   

 A simple p-n juction diode is fabricated by doping p and n type layers on a silicon or germanium wafer. The germanium and silicon materials are prefered for diode fabrication because:

· They are available in high purity.  ·  Slight doping like one atom per ten million atoms of a desired impurity can change the conductivity to a considerable level.· The properties of these materials change on applying heat and light and hence it is important in the devlopment of heat and light sensetive devices.

Diode circuit voltage measurements: (a) Forward biased. (b) Reverse biased.

A forward-biased diode conducts current and drops a small voltage across it, leaving most of the battery voltage dropped across the lamp. If the battery’s polarity is reversed, the diode becomes reverse-biased, and drops all of the battery’s voltage leaving none for the lamp. If we consider the diode to be a self-actuating switch (closed in the forward-bias mode and open in the reverse-bias mode), this behavior makes sense. The most substantial difference is that the diode drops a lot more voltage when conducting than the average mechanical switch (0.7 volts versus tens of millivolts).

This forward-bias voltage drop exhibited by the diode is due to the action of the depletion region formed by the P-N junction under the influence of an applied voltage. If no voltage applied is across a semiconductor diode, a thin depletion region exists around the region of the P-N junction, preventing current flow. (Figure below (a)) The depletion region is almost devoid of available charge carriers, and acts as an insulator:

 Diode representations: (a) PN-junction model, (b) schematic symbol.

The schematic symbol of the diode is shown in Figure above (b) such that the anode (pointing end) corresponds to the P-type semiconductor at (a). The cathode bar, non-pointing end, at (b) corresponds to the N-type material at (a). Also note that the cathode stripe on the physical part (c) corresponds to the cathode on the symbol.

If a reverse-biasing voltage is applied across the P-N junction, this depletion region expands, further resisting any current through it. (Figure below)

Depletion region expands with reverse bias.

Conversely, if a forward-biasing voltage is applied across the P-N junction, the depletion region collapses becoming thinner. The diode becomes less resistive to current through it. In order for a sustained current to go through the diode; though, the depletion region must be fully collapsed by the applied voltage. This takes a certain minimum voltage to accomplish, called the forward voltage as illustrated in Figure below.

Inceasing forward bias from (a) to (b) decreases depletion region thickness.

For silicon diodes, the typical forward voltage is 0.7 volts, nominal. For germanium diodes, the forward voltage is only 0.3 volts. The chemical constituency of the P-N junction comprising the diode accounts for its nominal forward voltage figure, which is why silicon and germanium diodes have such different forward voltages. Forward voltage drop remains approximately constant for a wide range of diode currents, meaning that diode voltage drop is not like that of a resistor or even a normal (closed) switch. For most simplified circuit analysis, the voltage drop across a conducting diode may be considered constant at the nominal figure and not related to the amount of current.

Actually, forward voltage drop is more complex. An equation describes the exact current through a diode, given the voltage dropped across the junction, the temperature of the junction, and several physical constants. It is commonly known as thediode equation:

The term kT/q describes the voltage produced within the P-N junction due to the action of temperature, and is called thethermal voltage, or V_t of the junction. At room temperature, this is about 26 millivolts. Knowing this, and assuming a “nonideality” coefficient of 1, we may simplify the diode equation and re-write it as such:

You need not be familiar with the “diode equation” to analyze simple diode circuits. Just understand that the voltage dropped across a current-conducting diode does change with the amount of current going through it, but that this change is fairly small over a wide range of currents. This is why many textbooks simply say the voltage drop across a conducting, semiconductor diode remains constant at 0.7 volts for silicon and 0.3 volts for germanium. However, some circuits intentionally make use of the P-N junction’s inherent exponential current/voltage relationship and thus can only be understood in the context of this equation. Also, since temperature is a factor in the diode equation, a forward-biased P-N junction may also be used as a temperature-sensing device, and thus can only be understood if one has a conceptual grasp on this mathematical relationship.

A reverse-biased diode prevents current from going through it, due to the expanded depletion region. In actuality, a very small amount of current can and does go through a reverse-biased diode, called the leakage current, but it can be ignored for most purposes. The ability of a diode to withstand reverse-bias voltages is limited, as it is for any insulator. If the applied reverse-bias voltage becomes too great, the diode will experience a condition known as breakdown (Figure below), which is usually destructive. A diode’s maximum reverse-bias voltage rating is known as the Peak Inverse Voltage, or PIV, and may be obtained from the manufacturer. Like forward voltage, the PIV rating of a diode varies with temperature, except that PIV increases with increased temperature and decreases as the diode becomes cooler—exactly opposite that of forward voltage.

Diode curve: showing knee at 0.7 V forward bias for Si, and reverse breakdown.

Typically, the PIV rating of a generic “rectifier” diode is at least 50 volts at room temperature. Diodes with PIV ratings in the many thousands of volts are available for modest prices.

                                                                                                                                                                         #Team Circuitready

Inductor (L)

Inductor

Inductor is an electrical component that stores energy in magnetic field.

The inductor is made of a coil of conducting wire.

In an electrical circuit schematics, the inductor marked with the letter L.

The inductance is measured in units of Henry [L].

Inductor reduce current in AC circuits and short circuit in DC circuits.

Inductor symbols

Inductor
Iron core inductor
Variable inductor

Inductors in series

For several inductors in series the total equivalent inductance is:

L_Total = L₁+L₂+L₃+...

Inductors in parallel

For several inductors in parallel the total equivalent inductance is:

Inductor's voltage

Inductor's current

Energy of inductor

AC circuits

Inductor's reactance

X_L = ωL

Inductor's impedance

Cartesian form:

Z_L = jX_L = jωL

Polar form:

Z_L = X_L∠90º

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What is a Capacitor (C)..?

What is capacitor

Capacitor is an electronic component that stores electric charge.                                                                                                                       The capacitor is made of 2 close  conductors (usually plates) that are separated by a dielectric material. The plates accumulate electric charge when connected to power source. One plate accumulates positive charge and the other plate accumulates negative charge.

The capacitance is the amount of electric charge that is stored in the capacitor at voltage of 1 Volt.

The capacitance is measured in units of Farad (F).

The capacitor disconnects current in direct current (DC) circuits and short circuit in alternating current (AC) circuits.

Capacitor symbols

Capacitor
Polarized capacitor
Variable capacitor

Capacitance

The capacitance (C) of the capacitor is equal to the electric charge (Q) divided by the voltage (V):

C is the capacitance in farad (F)

Q is the electric charge  in coulombs (C), that is stored on the capacitor

V is the voltage between the capacitor's plates in volts (V)

Capacitance of plates capacitor

The capacitance (C) of the plates capacitor is equal to the permittivity (ε) times the plate area (A) divided by the gap or distance between the plates (d):

C is the capacitance of the capacitor, in farad (F).

ε is the permittivity of the capacitor's dialectic material, in farad per meter (F/m).

A is the area of the capacitor's plate in square meters (m²].

d is the distance between the capacitor's plates, in meters (m).

Capacitors in series

 

The total capacitance of capacitors in series, C1,C2,C3,.. :

Capacitors in parallel

The total capacitance of capacitors in parallel, C1,C2,C3,.. :

C_Total = C₁+C₂+C₃+...

Capacitor's current

The capacitor's momentary current i_c(t) is equal to the capacitance of the capacitor,

times the derivative of the momentary capacitor's voltage v_c(t):

Capacitor's voltage

The capacitor's momentary voltage v_c(t) is equal to the initial voltage of the capacitor,

plus 1/C times the integral of the momentary capacitor's current i_c(t) over time t:

Energy of capacitor

The capacitor's stored energy E_C in joules (J) is equal to the capacitance C in farad (F)

times the square capacitor's voltage V_C in volts (V) divided by 2:

E_C = C × V_C ² / 2

AC circuits

Angular frequency

ω = 2π f

ω - angular velocity measured in radians per second (rad/s)

f  - frequency measured in hertz (Hz).

Capacitor's reactance

Capacitor's impedance

Cartesian form:

Polar form:

Z_C = X_C∟-90º

Capacitor types

Variable capacitor	Variable capacitor has changeable capacitance
Electrolytic capacitor	Electrolytic capacitors are used when high capacitance is needed.  Most of the electrolytic capacitors are polarized
Spherical capacitor	Spherical capacitor has a sphere shape
Power capacitor	Power capacitors are used in high voltage power systems.
Ceramic capacitor	Ceramic capacitor has ceramic dielectric material. Has high voltage functionality.
Tantalum capacitor	Tantalum oxide dielectric material. Has high capacitance.
Mica capacitor	High accuracy capacitors.
Paper capacitor	Paper dielectric material.

                                                                                                                         

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What is a Resistor (R)...?

Resistor is an electrical component that reduces the electric current.
The resistor's ability to reduce the current is called resistance and    is measured in units of ohms (symbol: Ω).
If we make an analogy to water flow through pipes, the resistor is
a thin pipe that reduces the water flow.

Ohm's law

The resistor's current I in amps (A) is equal to the resistor's voltage V in volts (V)
divided by the resistance R in ohms (Ω):


The resistor's power consumption P in watts (W) is equal to the resistor's current I in amps (A)
times the resistor's voltage V in volts (V):

P = I × V

The resistor's power consumption P in watts (W) is equal to the square value of the resistor's current I in amps (A)
times the resistor's resistance R in ohms (Ω):

P = I ² × R

The resistor's power consumption P in watts (W) is equal to the square value of the resistor's voltage V in volts (V)
divided by the resistor's resistance R in ohms (Ω):

P = V ² / R

Resistors in parallel

The total equivalent resistance of resistors in parallel R_Total is given by:

So when you add resistors in parallel, the total resistance is decreased.

Resistors in series

The total equivalent resistance of resistors in series R_total is the sum of the resistance values:

R_total = R₁+ R₂+ R₃+...

So when you add resistors in series, the total resistance is increased.

Dimensions and material affects

The resistance R in ohms (Ω) of a resistor is equal to the resistivity ρ in ohm-meters (Ω∙m) times the resistor's length l in meters (m) divided by the resistor's cross sectional area A in square meters (m²):

Resistor symbols

	Resistor (IEEE)	Resistor reduces the current flow.
	Resistor (IEC)
	Potentiometer (IEEE)	Adjustable resistor - has 3 terminals.
	Potentiometer (IEC)
	Variable Resistor / Rheostat (IEEE)	Adjustable resistor - has 2 terminals.
	Variable Resistor / Rheostat (IEC)
	Trimmer Resistor	Presest resistor
	Thermistor	Thermal resistor - change resistance when temperature changes
	Photoresistor / Light dependent resistor (LDR)	Changes resistance according to light

Resistor color code

The resistance of the resistor and its tolerance are marked on the resistor with color code bands that denotes the resistance value.
There are 3 types of color codes:

• 4 bands: digit, digit , multiplier, tolerance.
• 5 bands: digit, digit, digit , multiplier, tolerance.
• 6 bands: digit, digit, digit , multiplier, tolerance, temperature coefficient.

Resistance calculation of 4 bands resistor

R = (10×digit₁ + digit₂) × multiplier

Resistance calculation of 5 or 6 bands resistor

R = (100×digit₁ + 10×digit₂+digit₃) × multiplier

Resistor types

Variable resistor	Variable resistor has an adjustable resistance (2 terminals)
Potentiometer	Potentiometer has an adjustable resistance (3 terminals)
Photo-resistor	Reduces resistance when exposed to light
Power resistor	Power resistor is used for high power circuits and has large dimensions.
Surface mount (SMT/SMD) resistor	SMT/SMD resistors have small dimensions. The resistors are surface mounted on the printed circuit board (PCB), this method is fast and requires small board area.
Resistor network	Resistor network is a chip that contains several resistors with similar or different values.
Carbon resistor
Chip resistor
Metal-oxide resistor
Ceramic resistor	#Team Circuitready