Rectifier

Coding of the diodes according to two standards

The value of the diodes can be indicated in several ways:
maybe in light according to a standardized coding
maybe in code of colors.
Display in light, standard JEDEC or Pro-Electron
No difficulty to read the value of the diode, with less of course than half of the characters was unobtrusive with time or a blade. All in all, two standards for two types of denomination:
The diodes in accordance with the American standard start with 1N and end in a sequence number.
The diodes according to the European standard start with two or three letters and also end in a sequence number.
Display in code of colors

The coding of the value of the diode is carried out with four rings of color. Among these four rings, one or two is broader than the others, which makes it possible to know by where to begin the reading. The side where is the broadest rings corresponds to cathode (K).
Only one ring is broader than the others, we are in the presence of a diode whose marking is standardized according to an American coding, and the name of the diode always starts with 1N.
Two rings are broader than the others, we are in the presence of a diode whose marking is standardized according to a European coding, and the name of the diode starts with three (two plus one) letters.
Correspondence between colors and values

Notation component

Notation "Pro-Electron" (name starting with the letter has, B, C, or R.)
Notation according to standard JEDEC (Joined Electron Device Engineering Council (2N2222).
Japanese notation, with a name starting with xSx (2SAxxxx, 2SCxxxx), according to standard JIS (Japanese Industrial Standard).
Name starting with three letters TIP (Texas Power Instrument). (TIP31A, TIP42)

Notation "Pro-Electron"

Format: 2 letters, ]letter_, Serial number (or Series code), ]Suffix_:
R = ]third letter_
F = second letter
B = first letter
First letter
The first letter indicates material used for the active part of the component
With = Germanium (from now on very little used) or another material whose forbidden band lies between 0,6 and 1,0 eV.
B = Silicon (couremment used nowadays) or another material whose forbidden band lies between 1,0 and 1,3 eV.
C = gallium Arsenure or another material whose forbidden band is higher than 1,3 eV.
D = Salts, such as Sulphurizes cadmium, Antimonide of indium or another material whose forbidden band is lower than 0,6 eV.
R = made up Materials (for example cadmium Sulfide). Application principal: detector of radiations, photograph-conductive cells, generators ⁄ sensors Hall.
Second letter
The second letter indicates the principal function of the component (standard ⁄ application)
With = Diode signal or diode low power.
B = Diode with variable capacity (Varicap).
C = Transistor BF (Low frequency), small signals (low power)
D = Transistor BF of power
E = Diode with tunnel effect
F = Transistor HF (High frequency), low power
G = Devices multiple compounds of dissimilar elements (oscillating or networks of transistors, for example).
H = Diode for measurement of magnetic field (field honest)
K = Component with Hall effect
L = Transistor HF strong power
M = Multiplying and modulating Hall
NR = Optocoupleurs (also called photocoupleurs).
P = Photodiode, phototransistor, photoresistance (LDR), Component sensitive to radiations ⁄ radiations
Q = Generating of radiation ⁄ radiation (LED, for example)
R = commutation and Control device (thermal resistance jb > 15K ⁄ W) low power
S = Transistor of commutation low power
T = commutation and Control device (thermal resistance jb > 15K ⁄ W), triacs, thyristor strong power, Schottky diode, diode PNPN
U = Transistor of commutation strong power
X = multiplying Diode (varactor, diode of recovery)
Y = recovery or rectifier Diode, strong power (often fast)
Z = Diode of reference or voltage regulation (for example Zener). If 3rd letter = W, then diode of chopping.
Code command
The code of command can be made up of three digits or a letter followed by two digits:
3 digits: number ranging between 100 and 999. There does not exist particular logic for the attribution of this number, which remains with the "discretion" of the manufacturer. These three figures indicate that it is about a component rather intended for the general public.
Letter + 2 digits: W, X, Y or Z, followed by a number ranging between 10 and 99, This code indicate that it is about a component intended for the professional or industrial applications. The letter L is reserved for the lasers diode, the letter T is reserved for LEDs three states or trichromatic, the letter W is reserved for the diodes of chopping. The other letters do not have precise significance.
Complementary letter_
This letter, when it exists, indicates a light electric or mechanical variation compared to the basic component. It does not have precise significance, except for the letter R which always indicates an opposite polarity.
A under-classification can be used for products which comprise several alternatives. This suffix depends on the component:
Diode of reference and voltage regulation (Zener): suffix made up of 1 letter and 1 number.
The definite letter the tolerance: To = 1% (E96 series)
B = 2% (E48 series)
C = 5% (E24 series)
D = 10% (E12 series)
E = 20% (E6 series)
The number indicates Zener the typical tension of work. The letter V replaces the decimal point (for example 5V1 for 5,1V).
Diode of chopping: suffix made up of 1 number, which definite the maximum tension reverses uninterrupted (Vr). As for the zener diode, the letter V replaces the decimal point.
Rectifier diode and thyristor: suffix made up of 1 number, which indicates the value of the opposite tension of maximum repetitive peak (Vrrm) or the value of the tension of repetitive peak at the blocked state (Vdrm).
Detectors of radiation : a hyphen (-) followed by a number indicating the width of zone deserted out of micrometers. An additional letter can be added to specify the resolution.
Network of generators and detectors of radiations: a bar of fraction ( ⁄ ) followed by a number indicating of how much elements the network is made up.

Notation JEDEC

Format: Quantify, Lettre, Serial number, ]Suffix_
Examples: 2N2222
First figure
Indicate the number of effective electric connections, less one (figure 2 indicates that there are 3 legs). Figures 4,5 and 6 are reserved to the optocoupleurs
Letter
It is always about the letter "NR".
Serial number
The serial number can take a value ranging between 100 and 9999. There either there does not exist particular logic for the attribution of this number, which remains with the "discretion" of the manufacturer. One can however notice that the numerical command corresponds grosso-modo to the order of appearance in time.
]Suffix_
The suffix indicates the fork of gain (hFE) of the transistor, as for the notation Pro-Electron:
With = weak gain
B = average gain
C = high gain
Nothing (no letter) = the gain can be high, average or high (transistor not sorted by the manufacturer)

Japanese notation:

Quantify, 2 letters, Serial number, ]Suffix_
Examples: 2SA494, 2SC690
First figure
Indicate the number of effective electric connections, less one (figure 2 indicates that there are 3 legs).
2 - For a semiconductor recorded under the EIAJ, this letter is always an S
If not, I do not know
3 - Third letter: Polarity and application (use)
4 - Order of application for recording EIAJ.
The serial number can take a value ranging between 10 and 9999.
5 - Level (or degree) of improvement
An improved component can be used instead of a component of the former generation, but the reverse is not forcing possible.
With = Transistor PNP, high frequency
B = Transistor PNP, low frequency
C = Transistor NPN, high frequency
D = Transistor NPN, low frequency
E = Diode
F = Thyristor
G = Gunn Component
H = Transistor UJT (Double-base diode)
J = FET or MOS-FET Channel P
K = FET or MOS-FET Channel NR
M = bidirectional Thyristor
Q = LED
R = rectifier Diode
S = Diode signal
T =?
V = Varicap Diode
Z = Zener diode

Rectifier with diodes

To convert a AC current into an one-way current.
There exist two categories of rectifiers, mainly used into alternate sinusoidal:
Rectifiers mono alternation, for the single-phase currents, or three-phase.
The rectifiers Bi alternation, for the single-phase currents, or three-phase.

Basic rule:

To block the passage of the current for an alternation, the structures mono alternation.
To block the passage of the current and to force it to change direction for each alternation, the structures bi.alternance.
Recall: A diode is a semiconductor dipole. who lets pass the current only in one direction. It is characterized by the bearable maximum current and its electric characteristics Vd, Rd in the busy direction, by the bearable maximum tension in reverse.
Symbol:

Rectifiers mono alternation.

Rectifier in single-phase current:
That is to say the assembly:
Curves obtained:
Characteristic sizes:
Vs max = Ve max - Vd ( 0.7 Vd 1V )
Vs effective Ve effictive ⁄ 2 Vs RMS is measured with a voltmeter or ferromagnetic.
Vs average Ve maxi ⁄ π Vs average is measured with a voltmeter positioned
There exists the possibility for a diode of supporting a short overcurrent because it has a characteristic product I².t (I is the value of overcurrent and T maximum time before breakdown). To refer to the documents manufacturers.

Rectifier in three-phase current


Curves obtained:


The neutral is often joined together with the ground, it is dangerous to touch a phase, there is risk of indirect electrocution. It should be checked if that is the case.

Characteristic sizes:

Vs maxi = Ve maxi - Vd ( 0.7 Vd 1V ) Vs is measured with an oscilloscope.
Vs mini = Ve maxi ⁄ 2 - Vo Vs is measured with an oscilloscope.
The diodes lead to T ⁄ 6,3T ⁄ 6,5T ⁄ 6, 7T ⁄ 6  
Vs average 1.013. Ve (eff) Vs average is measured with a voltmeter set to DC.
Vs effective Ve (eff) . 1.17 Vs effective is measured with a voltmeter set to AC

Features necessary for the diode:

To be able to support:
Tension inverse ≈ Ve maxi √3 = Ve effective * √6
because two phases provide a made up power:
Ve effective between phase and neutral * √3
Maximum intensity crossing the load. There exists the possibility for the diodes of supporting a short overcurrent because it has a characteristic product I² .t (I is the value of overcurrent and T maximum time before breakdown.

Rectifiers Bi alternation.

Rectifiers single-phase current bialternance:
There exist two assemblies of bases:
The structure with bridge of GRAETZ and the structure at point medium, of which the curves characteristic appear Ci below.

Assembly with bridge of GRAETZ.

Characteristic sizes:

Vs max = Ve max - 2 . Vd(0.7 Vd 1V ) Two diodes work by alternation.
Vs is measured with an oscilloscope.
Vs mini = 0V Vs is measured with an oscilloscope.
Vs effective Ve maxi ⁄ √2 Effective Vs is measured with a voltmeter
RMS or ferromagnetic.
Vs average = 2 * Ve maxi ⁄ π Average Vs is measured with a voltmeter
positioned in DC

Features necessary for the diode:

To be able to support
A tension reverses³ maximum Ve and the maximum intensity crossing the load.
There exists the possibility for a diode of supporting a short overcurrent, because it has a characteristic product I² .t (I is the value of overcurrent and T maximum time before breakdown). To refer to the documents manufacturers.

Rectifiers at point medium.

The results and curves obtained are strictly identical to the preceding assembly. The differences are:
Only one Vd tension is to be cut off instead of two.
Two diodes instead of four. The assembly was imagined starting from the rectifier mono alternation single-phase current.
The source must provide two strictly identical feedings with Ve.
Both Ve must be referred at a point common medium.
Structure:

Characteristic sizes:

Vs maxi = Ve maxi -Vd (0.7 Vd 1V ) Vs is measured with an oscilloscope.
Vs mini = 0V Vs is measured with an oscilloscope.
Vs effective Ve maxi ⁄ √2 Vs effective is measured with a voltmeter
RMS or ferromagnetic.
Vs average = 2 * Ve maxi ⁄ π Vs average is measured with a voltmeter
positioned DC

Features necessary for the diode

To be able to support:
A tension reverses³ maximum Ve and the maximum intensity crossing the load.
There exists the possibility for a diode of supporting a short overcurrent, because it has a characteristic product I² .t (I is the value of overcurrent and T maximum time before breakdown). To refer to the documents manufacturers.

Rectifiers Three-phase current Bi alternation:

That is to say the following assembly: (The neutral is not used)
The neutral is often joined together with the ground, it is dangerous to touch a phase, there is risk of indirect electrocution. It should be checked if that is the case.

Curves obtained


Characteristic sizes:
Vs max= (Ve maxi * √3) - 2 * Vo
Ve measured between phase and neutral.
Two diodes working alternately.
Vs is measured with an oscilloscope.
Vs mini 90 % de Vs maxi Vs is measured with an oscilloscope.
Vs average 3 * Ve maxi * √3 ⁄ π ≈ V entre phase * 0.95
Ve measured between phase and neutral.
Vs average is measured with a voltmeter set to DC
Vs effective Vs average Vs effective is measured with a voltmeter set to AC.
The output voltage can be used directly without filtering.

Features necessary for the diodes:

To be able to support:
A tension reverses³ and the maximum intensity crossing the load.
There exists the possibility for a diode of supporting a short overcurrent because it has a characteristic product I² .t (I is the value of overcurrent and T maximum time before breakdown). To refer to the documents manufacturers.

Presentation

The diode Zener (also called diode of regulation) behaves a little like a traditional diode, since it leads in only one direction (direct direction) as soon as the tension present at its terminals exceeds the direct tension of threshold, which is about 0,6 V. But there stops the resemblance, because a zener diode can also lead in the other direction (opposite direction) as soon as the value of the opposite tension exceeds a certain threshold, called tension of Zener. It is the case also diodes traditional, you will think, except that for these last, one avoids reaching this threshold of opposite tension, because the diode high risk of claquer of a blow and this in an irreversible way. Whereas for the zener diode, the attack of the tension of Zener is the required effect.

Standardized values

Certain zener diodes is more répendues that others, it is the case for example of those which constitute series BZX55C (series C, tolerance +-5%). The values which one can record in this category are those of the E24 series of 2,4 V with 75 V. In fact, one finds values being low (0,7 V) and much higher (200 V or more). That of 0,7 V to the characteristic to have to be connected "with back" because it functions in direct direction.

Tolerance on the displayed tension

The tolerance on the Zener tension is rather broad, and a marked diode 6,8 V can - with the same ambient temperature of 25 °C - present very well a tension ranging between 6,4 V and 7,2 V. In the same way, a Zener marked 82 V can present a tension ranging between 77 V and 87 V. the tolerance correspond normally to the E24 series which specifies an accuracy of 5%. Normally, the manufacturers indicate in their technical papers for which current the displayed tension is valid.

Resistance interns (dynamic) diode

The internal resistance (dynamic) of the diode is not null, and from this fact the tension present at its terminals varies according to the current which crosses it. The value of this internal resistance is not fixed and depends on the current which crosses the diode, as of the frequency of the current if this last "is modulated" (to 1 Khz, dynamic resistance is lower than uninterrupted). Certain manufacturers indicate the various values of dynamic resistance according to the current and at a given frequency. For example dynamic resistance lower than 50 ohms with 1 Khz and lower than 1000 ohms uninterrupted, with a current of 5 my in both cases.

Maximum current

When one buys a zener diode, one sees only seldom the value maximum of the current which can cross it. Instead of that, the manufacturer (and the retailer) indicate the tension and the power of the zener diode. It is with these two values that one deduces the maximum current, with the following formula: Imax = Pmax/Uzener
For a zener diode of 12 V belonging to a series of power 400 MW, the calculation of the current max give this: Imax = 0,4 ⁄ 12 = 33 my
And for a zener diode of 12 V belonging to a series of power 1,3W, the calculation of the current max gives this: Imax = 1,3 ⁄ 12 = 108 my
These values are values accepted in continuous mode. If the diode is welded onto the circuit with legs remained rather long and if that lasts little of time (10 ms with more), the maximum current can reach a double value or triple. Let us note that like the current max depends on the tension of Zener, one will quite naturally have in the same series of power (for example 1,3 W) a current max which will go reducing itself as the Zener tension increases. Thus in same series BZX85C, a zener diode of 3,6 V agrees to function with a current of 290 my (2,6 has max during a very short time), whereas with a zener diode of 62 V one should not exceed 16 my (180 my max during a very short time).

Use in voltage regulation

A zener diode is mainly used in the regulation of feeding, where it can be used as a recluse or coupled with a transistor of average or large power.

Regulation of supply recluse

The zener diode can be placed in parallel on the terminals of feeding, with a resistance upstream intended to limit the current which can cross it (especially when nothing is connected at output and that it is the Zener who must absorb all the current):
It is about the way simplest to use a zener diode to control a tension, but the resistance of limitation of R1 current must hold account: current which crosses the Zener: it must however have a rather low value so that the diode makes its job of regulation well, but not too low so that the diode does not roast), of the current absorptive by the load (the fed circuit). This type of circuit is hardly appropriate when one does not know the current consumed at output, and even less when the consumed current can vary in great proportions.

Regulation of feeding supported by a buddy strapping man

The zener diode can also be associated with a "ballast" (transistor of power) to amplify the current délivrable by the feeding:
With this assembly, current criterion the "of output" is much less critical, because the current fluctuations at output are reflected with a factor of division equal to the gain of the transistor: for example, if the transistor with a gain while running from 100, a current fluctuation at output of 100 my to 200 my results in a variation on its basis reduced to an amplitude of 1 my. But it is necessary all the same to think of taking into account the voltage drop base-transmitter of the transistor, who is about 0,6 V (1,2 V if it is about a transistor darlington). If you wish to obtain a output voltage of 5 V with a traditional bipolar transistor (2N1711 for example), you must use a zener diode of 5,6 V (that falls well, such a diode exists). If you employ a zener diode of 12 V, the output voltage will be reduced to 11,4 V approximately.
Nothing prevents you cabling several zener diodes and from commutating one of them among all, to profit from adjustable output voltage an "fixes", as shows it the following diagram:

Easy to use

but not perfect, the zener diode constitutes simple means of being made a small controlled feeding, but presents the main drawback of a bad stability of its nominal voltage according to the ambient temperature and of the current which crosses it. It is thus appropriate for the assemblies of which the stability of the supply voltage is not critical (small radio for example) or for the assemblies whose consumption varies very little. Zener diodes of power are sometimes used in parallel on the bulbs of some two wheels motorized equipped with battery, to protect them from overpressures.

Regulation of improved feeding

Since the terminal voltage of a zener diode depends to a certain extent current which crosses it, one can make so that this current varies little, even when the tension upstream of the regulation varies much. That is possible thanks to the use of a generator of constant current, which one can work out with a pair of bipolar transistors, a single transistor FET or with an integrated voltage regulator.
The diagram which follows watch an example of such a structure, with a field-effect transistor (FET) of 2N3819 type.
This type of assembly functions very well, the current crossing the zener diode lies between 5 my and 15 my, and depends much on the FET used. By using two FET of the same model coming from the same manufacturer, you can belong to the important variations. But that is not critical in this case, because the important thing is that the current stable remainder, even if its value is not known (or foreseeable) with an greater accuracy. An assembly where the current is more easily skeletal and "foreseeable" is presented hereafter. It implements an integrated voltage regulator of type LM317 assembled out of generator of constant current.
As the tension presents between the output of the regulator (limits 2) and its Ajust input (1 limits) is always of 1,25 V, the current which circulates in R1 depends only on the value of this resistance. Thus, if R1 is worth 120 ohms, the generated constant current will be of: Iconst = 1.25 ⁄ 120 = 10 my.

Warning

On the last three assemblies proposed, which call all upon a transistor of power, the current consumed by the transistor itself through its basic connection, cannot be been unaware of, especially if the apparatus to be fed is large-scale consumer of current. Admit that one uses a transistor of power having a gain of 50, which delivers via its transmitter a current of 1 has, that means that its base absorbs a current from approximately 20 my.
This case can seem extreme but however thus think well of dimensioning the generator of constant current to enable him to meet the needs for the zener diode and the transistor. Another thing: this kind of preliminary calculation applies for a load connected at output permanently. If you envisage a fort running in the base of the transistor (extremely compared to the current crossing the zener diode itself), think so that the diode will owe subire if the load is disconnected (following breakdown or fusible fusion of protection).
The solution making it possible to free itself from this kind of consideration is to use a transistor with greater gain (a single transistor darlington or several traditional transistors assembled in darlington). In this case, the effect of the output current on the base of "the first" transistor is less and the possible variations of current, weaker, pose much less problems. But of course, the voltage drop "base-transmitter" becomes more important and there it is necessary still to hold account of it.

Other uses

The zener diode can also be employed where a reference voltage standard is necessary, in the comparison of tension compared to one or more fixed values, or even in the "subtraction" of a tension.

Comparison of tension

Employee with a comparator of tension (or a AOP assembled like such), the zener diode can constitute stable a enough reference for many applications (level gauge weak, or indicating battery of going beyond of threshold of a tension under monitoring, for example). The diagram which follows met of work a diode Zener (D1) like reference voltage standard:

"Subtraction" of a tension

A Zener placed in series in a circuit, can allow to shift a fixed voltage or variable. It is necessary obviously that the tension "to be attenuated" has a sufficient amplitude compared to the tension of Zener, unless the required effect is "to cut" the signal in lower part of a certain threshold. The zener diode can in the same spirit, to prevent the release of a circuitery when a tension of command presents a too important electrode bias.
For example, a tension of command of 2,5V at rest and 12V to work, can be brought back to a tension of 0V at rest and of 8,7V to work, by putting in series a zener diode of 3V3 (by connecting it in the opposite direction, because in the direct direction, the voltage drop would be only of 0,6V). The diagram which follows met of work a diode Zener (D1) like subtracter of tension:
In this assembly, the tension at "output" of the zener diode (on the basis of Q1) is equal to the tension applied to its "input" (cursor of RV1), from which one withdraws the value of the Zener tension.

Presentation

A diode component is said active, which belongs to the family of the semiconductors. By definition, a diode refers to any electronics component equipped with two electrodes. It is about a polarized component which thus has two electrodes, an anode and a cathode. Cathode (sometimes called K, for Kathode) is located by a ring of location.
A diode does not let pass the current in the same way according to whether one connects it in a direction or the other. This characteristic makes it possible the diode to be used to rectify a AC current, that is to say to let pass only the positive half-wave or that negative half-wave (according to the orientation of the diode). The material more used to manufacture the diodes "standard" is to date silicon, germanium from now on being much less used than in the past.

Main features of a diode

There exists a multitude of diodes, to see paragraphs which follow. The type of diode to be used depends on the application: detection of signals RF in a radio receiver, rectification in a linear feeding, speed improvement of commutation of transistors of power in a feeding with cutting, overpotential protection, for example.

The tension of threshold

Corresponds to the tension from which the diode starts to lead when it is polarized in the busy direction. Known as differently and in manner undoubtedly just: a diode leads only when its anode is carried to a potential more positive than its cathode, and than the potential difference between anode and cathode reaches the tension of threshold.
The two diagrams which follow use two different diodes which are traversed by a different current, and show the voltage drops introduced by these diodes. One can thus say that the tension of threshold corresponds to the minimal tension of operation below which the diode cannot be used. This tension of threshold also corresponds to the tension of waste, that is to say the tension which will be lost because of the use even of the diode. The more important the current which crosses the diode is, and the more important the voltage drop is. The evolution of the voltage drop remains however rather weak compared with the evolution of the current.

The diode used here is a traditional diode known as of commutation, models 1N4148. The voltage drop which it introduces is of some dizièmes of volts, when the current which it cross-piece is of some my.

The diode used here is a traditional diode known as of rectification, models 1N4007. The voltage drop which it introduces is about the volt, when the current which it cross-piece is of a few hundreds of my.
Note: the resistances placed on the preceding diagrams represent the load, that is to say the circuit which is fed through the diodes. In the first case, the value of resistance is higher because a commutation diode is in general not used for important currents, whereas a rectifier diode can be crossed by currents of several hundred milliamperes or several amps.

The opposite tension

Also called tension of breakdown. A "normal" diode is likely to roast when this maximum opposite tension is exceeded, but certain diodes support this operation and were even designed to work in this way.
The zener diodes, for example, behave as normal diodes when one connects them in the direct direction, and present a tension rightly called tension of Zener, when one connects them in the opposite direction. This opposite tension (of Zener) is used as reference of tension, for regulation of feeding for example.

The forward current

It is about the maximum intensity which can traverse the component continuously when he is polarized in the busy direction, without this last not roasting. The diode can in general support an current surge (very brêve) quite higher than the maximum current.

Diodes VHV

Diodes VHV are diodes able to work under very high voltages (THT), several Kv with several tens of Kv. It is rather rare to find a diode which only allows that it. Most of the time, it acts several diodes assembled in series, in the same case. Besides one calls sometimes this type of component a bar of diodes. The representation of this type of diode in an electronic assembly is often made by several diodes stuck between them, in series:

Diode of detection

The diodes of detection are used for detection (demodulation) RF in the stages of input of receiver of radio. This type of diode, generally out of germanium, presented a weaker threshold of conduction (0,2V with 0,3V) that those of the diodes to silicon (0,6V with 0,7V) and thus had the advantage of being more sensitive and thus of better functioning with low levels of reception.

Networked diodes

Plusieures diodes are assembled in the same case.
Either they are completely isolated the ones from the others, or they have one of their shared leg (network with common cathode or common anode). When one speaks about networked diodes, it is generally about a case comprising four, seven or eight diodes. But there exist also cases comprising only two diodes, rises head-digs, that one finds in particular in the field of the rectification of power (out of case TO220), or in the field HF with the diodes varicaps.

Zener diode

The zener diodes are mainly used for the voltage regulation of feeding.

Diodes of reference of tension

These diodes have similar features with the zener diodes, but are characterized by a temperature coefficient much lower. The tension on their terminals, for a given current, thus varies less according to the ambient temperature. One uses them mainly in the field of the instrumentation, notement as far as temperature or more simply still of tensions (voltmeters).

Varicap diode


Notation symbolic of a diode varicap
A diode varicap (of variable English capacity), also named varactor (acronym of variable reactor) or diode with variable capacity is a type of diode which has the effect of behaving as a capacitor whose value of the capacity varies with the opposite tension applied on its terminals. This diode can be regarded as a variable capacitator. This type of diode is often used in assemblies radio frequency (RF) but also for applications to very high frequencies.
Operation
When the diode varicap is polarized in reverse (blocked direction), it functions as a capacitor whose capacity is adjustable according to the tension (negative) applied to the diode. That results from the variation of the zone of déplétion (or zone of space charge) according to the terminal voltage of the diode, because the variation of the width of this zone involves a variation of the capacity of the diode. Generally, the width of the zone of déplétion is proportional to the square root of the tension applied and the capacity is inversely proportional to this width. Thus the capacity of the diode is inversely proportional to the square root of the tension applied.
All the diodes have this property more or less, but the diodes varicap are optimized so as to obtain the desired capacity and a good variability of this one. Whereas in a traditional diode the capacity is reduced to the maximum.
However all the diodes varicaps are not diodes. In technology COMPLEMENTARY METAL OXIDE SEMICONDUCTOR, the varicaps can be formed in a way similar to transistors NMOS. that is to say with a strongly positively doped area (P+) placed inside a slightly negatively doped zone (NWELL), this type of varicap has a capacity similar to that of transistors NMOS; those comprise a strongly negatively doped zone (N+) located inside a zone slightly positively doped (PWELL) so as to form a jonctionP-N.
Uses
The diodes varicap are used in the circuits of agreement of the radio receivers and the television sets: they make it possible to vary the capacity of the circuit of agreement, and thus its frequency of resonance, by changing the tension of command applied to the diode (which comes from a potentiometer connected in general between the pole + and the pole - feeding).
In the receivers superheterodynes, they are at the same time used in the circuit of agreement of the stage of input and in the circuit of agreement of the local oscillator.
The diodes varicap gradually replaced the variable capacitators:
they are much smaller,
they are less expensive,
they do not wear (contrary to the variable capacitator which wears during the displacement of the blades).
They make it possible to carry out receivers with digital display: the tension of command comes from a digital-analog conversion of the selected frequency.
They have an small inconvenience: to cover a broadband, as the tape FM (88-108 MHz), they require a variation of high tension (typically 28 V). To obtain this tension starting from the supply voltage of the receiver (often 9 or 12 V), one can use a pump converter of load).
This type of diode is frequently used in assemblies RF to carry out a frequency modulation, or to ensure an agreement. But there exist also diodes varicap of power used to carry out multipliers of frequency to weak losses, and diodes varicap where the gallium arsenide is preferred with silicon for applications in very high frequency. In certain applications, it is necessary to use two assembled diodes varicap head-digs, which must have close characteristics. Certain manufacturers thus propose double or appairées diodes, and where the difference in capacity between the two diodes does not exceed 2,5%

Diode of protection

The Transil diode is the name given by Thomson to the Transzorb diode. This type of diode is of type "with avalanche" It is put in parallel on the feeding, and absorbs any overpressure. The main drawback of this type of diode is that a very strong overpressure puts it in short-circuit. There, it is sure that it protects still best the equipment which follows, but the fuses and circuit breakers which precede do not like that, and play their part well.

Electroluminescent diode (LED or LED)

A LED is a diode which emits visible radiations.


Photodiode

this type of diode is comparable to the photoresistive cells, in the direction or it is more or less conducting according to the intensity of the light which it receives. It can be in the form of a discrete component with two legs, or be integrated in a opto-coupler.

The photodiode PINE is a high-speed photodiode mainly used in the field of optics (infra-red notemment).

Diode Tunnel

The diode tunnel or Esaki diode is obtained starting from a degenerated layer P (NA > 1019 cm-3) and from a degenerated layer NR (ND > 1019 Cm3). Junction P+N+ thus obtained must be very abrupt and the ZCE present a very low thickness (qq tens of A°).
Under these conditions of the carriers can cross the barrier of potential by tunnel effect. The analysis specifies this effect requires the knowledge of quantum mechanics:

To obtain a tunnel effect it is necessary that:
the level of FERMI is located in BdV on the side P and BdC on the side NR
the thickness of ZCE is small so that the transition probability per tunnel effect is sufficient
with the same energy of the electrons are available in BdC and of the holes in BdV.
Consider a diode P+N+ unpolarized 0 K. This temperature is selected because all the levels in lower part of the level of FERMI are occupied, all the levels with the top are empty (figure a). Under these conditions, there is no effect of junction. the current which crosses the barrier is null because the number of electrons which go from P towards NR is the same one as the number of electrons which go from NR towards P.
In polarization (figure b), the current tunnel created by the electrons reverses which go from P towards NR is important., the diode does not block, the reverse current is important.
For the weak direct tensions (figure c), the current tunnel is generated by the electrons which go from NR towards P. But as the direct tension increases, the levels occupied in BdC will be found in front of levels of BI, the current tunnel will decrease (figure d).
For the intermediate direct tensions, the occupied levels of BdC find all in front of levels of BI and the current tunnel is dried up (figure E). The only possibility for the electrons of joining the side P of the junction is to cross the barrier of potential, one is found in the traditional case of on line polarized junction PN.
For the traditional direct tensions, the current tunnel is completely disappeared but the diffusion current is now notable and one finds the form characteristic of direct polarization.
Characteristic I (V) of this device thus presents on a small range of direct tensions a negative slope (the current decreases when the tension increases). The diode tunnel has a negative differential resistance (RDN).
As the time of transit per tunnel effect in the ZCE is very small, the RDN is independent of the frequency, diode ESAKI is very much used for the realization of oscillators, multivibrators, fast logical circuits and amplifiers ultra high frequencies low noise.

Backward diode

Also called Unitunnel diode. This diode is similar to the Tunnel diode in its total behavior, excluded that the portion "resistance negative" does not exist in the latter. This type of diode is particularly used for the rectification of signals of low amplitude and very high frequency

Schottky diode

A Schottky diode is a diode which has a maximum of direct tension very low and a very long switching time. This allows the detection of the weak signals HF and ultra high frequencies, making it useful for example in radioastronomy. One also uses it for his capacity to be let multiply by ten relatively strong intensities for the rectification of power.
 
 
History
The ancestor of the Schottky diode used two "natural" materials (a steel point and a crystal crystal), in the station with crystal.
Among the most current Schottky diodes, one finds the 1N5817, and of the junctions Schottky metal-semiconductor are present in the logical components of the 74S families, 74LS, 74F and 74AF for their switching speed high and their weak voltage drop.
Description and characteristics
A Schottky diode uses a junction metal-semiconductor (instead of a junction p-n like the conventional diodes). Whereas the standard silicon diodes have a tension of threshold of approximately 0.6 volt, the Schottky diodes have a tension of threshold (for a current of direct polarization from approximately 1 my) in the range of 0.15V with 0.45 V, which makes them useful in limitation of tension and prevention of saturation of the transistors. They also are very appreciated like commutation diodes (electronic of power) because of complete absence of opposite phenomenon of recovery of load.
The disadvantages of these diodes compared to the diodes with junction p-n are a tension of breakdown in weaker reverse, a current in polarization reverses higher, as well as an operating range in less important temperature. In spite of progress carried out, these diodes are thus more fragile under these conditions
Static protection (ESD)
A current use of the Shottky diodes is to protect the inputs from the components sensitive to the ESDs. In this assembly, two diodes in series between more and masses it with the input to be protected connected between the two diodes makes it possible to limit the tension on the input Vcc+Vseuil and GND-Vseuil. Their weak tension of threshold and their speed of commutation make them interesting for this kind of applications. However, they do not protect against from the events about the nanosecond or less.

Gunn diode

Oscillator microwave with negative resistance functioning according to the principle of the Gunn effect. It is about a diode made up of producing gallium arsenure of the oscillations coherent microwaves when fields electric important is applied to him.

Diode Pine


This type of diode can be used to ensure the optical detection of modulation (photodiode PINE at the entry of a receiver of a connection fiberoptic for example). It can also be used as element attenuator ordered in a stage HF, or like element of commutation for router of the signals HF.

Regulating diode of current

Diode with field effect whose characteristic is to generate a constant current, of which the value is independent of the tension applied on its terminals

Diac

A diac is a symmetrical diode made up of two assembled diodes of the Shockey type head-digs, and presents the caréctéristique one to be able to lead in the two directions, but only starting from one certain tension (between 25V and 40V, often 32V). This type of component is often used in series with the trigger of a thyristor or a triac

Several symbols were used to represent a diac. The symbol currently used that of the three is on the right represented on the left. This last is sometimes surrounded by a circle.

A diac does not have an inscription on its body. One recognizes it by a small tape (ring) right in the middle of the component. To compare with a diode whose ring is placed more close to an end.

Thyristor and Triac

The thyristor and the triac are in fact of the diodes ordered using a called additional electrode Gachette.

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