Diode Types and Their Uses

There are many different types of diodes that are available for use in electronics design. Different semiconductor diode types can be used to perform different functions as a result of the properties of these different diode types.

Semiconductor diodes can be used for many applications. The basic application is obviously to rectify waveforms. This can be used within power supplies or within radio detectors. Signal diodes can also be used for many other functions within circuits where the "one way" effect of a diode may be required.

Diodes are not just used as rectifiers, as various other types of diode can be used in many other applications. Some other different types of diodes include: light emitting diodes, photo-diodes, laser diodes and more as detailed in the list below.

Many of the different types of diodes mentioned below have further pages providing in-depth information about them including their structures, method of operation, how they may be used in circuits, and precautions and tips for using them in electronics design.



Types of diodes
It is sometimes useful to summarise the different types of diodes that are available. Some of the categories may overlap, but the various definitions may help to narrow the field down and provide an overview of the different diode types that are available.

•Avalanche diode: The avalanche diode by its very nature is operated in reverse bias. It uses the avalanche effect for its operation. In general the avalanche diode is used for photo-detection where the avalanche process enables high levels of sensitivity to be obtained, even if there are higher levels of associated noise.
•Laser diode: This type of diode is not the same as the ordinary light emitting diode because it produces coherent light. Laser diodes are widely used in many applications from DVD and CD drives to laser light pointers for presentations. Although laser diodes are much cheaper than other forms of laser generator, they are considerably more expensive than LEDs. They also have a limited life. See related articles list in left hand margin.
•Light emitting diodes: The light emitting diode or LED is one of the most popular types of diode. When forward biased with current flowing through the junction, light is produced. The diodes use component semiconductors, and can produce a variety of colours, although the original colour was red. There are also very many new LED developments that are changing the way displays can be used and manufactured. High output LEDs and OLEDs are two examples. See related articles list in left hand margin.
•Photo diode: The photo-diode is used for detecting light. It is found that when light strikes a PN junction it can create electrons and holes. Typically photo-diodes are operated under reverse bias conditions where even small amounts of current flow resulting from the light can be easily detected. Photo-diodes can also be used to generate electricity. For some applications, PIN diodes work very well as photo detectors. See related articles list in left hand margin.
•PIN diode: This type of diode is typified by its construction. It has the standard P type and N-type areas, but between them there is an area of Intrinsic semiconductor which has no doping. The area of the intrinsic semiconductor has the effect of increasing the area of the depletion region which can be useful for switching applications as well as for use in photo diodes, etc. See related articles list in left hand margin.
•Point contact diode: This type of diode is one of the most basic forms of diode in terms of its construction but it performs in the same way as a PN junction diode. This type of diode consists of a piece of N-type semiconductor, onto which a sharp point of a specific type of metal wire (group III metal) is placed. As this physical junction is formed, some of the metal from the wire migrates into the semiconductor and produces a PN junction. Point contact diodes have a very low level of capacitance because the resulting junction is very small. As such this type of diode is ideal for many radio frequency (RF) applications. The downside of the small junction is that they cannot carry high levels of current but they have the advantage that they are very cheap to manufacture, although their performance is not particularly repeatable.
•PN Junction: The standard PN junction may be thought of as the normal or standard type of diode in use today. These diodes can come as small signal types for use in radio frequency, or other low current applications which may be termed as signal diodes. Other types may be intended for high current and high voltage applications and are normally termed rectifier diodes. See related articles list in left hand margin.
•Rectifier diode: This definition refers to diodes that are used in power supplies for rectifying alternating power inputs. The diodes are generally PN junction diodes, although Schottky diodes may be used if low voltage drops are needed. They are able to rectify current levels that may range from an amp upwards.
•Schottky diodes: This type of diode has a lower forward voltage drop than ordinary silicon PN junction diodes. At low currents the drop may be somewhere between 0.15 and 0.4 volts as opposed to 0.6 volts for a silicon diode. To achieve this performance they are constructed in a different way to normal diodes having a metal to semiconductor contact. They are widely used as clamping diodes, in RF applications, and also for rectifier applications.
•Signal diode: This for of diode is used for small signal applications where small values of current are drawn. Diodes with the description of signal diode are generally the standard PN junction diode types.
•Step recovery diode: A form of microwave diode used for generating and shaping pulses at very high frequencies. These diodes rely on a very fast turn off characteristic of the diode for their operation.
•Tunnel diode: Although not widely used today, the tunnel diode was used for microwave applications where its performance exceeded that of other devices of the day. See related articles list in left hand margin.
•Varactor diode or varicap diode: This type of diode is used in many radio frequency (RF) applications. The diode has a reverse bias placed upon it and this varies the width of the depletion layer according to the voltage placed across the diode. In this configuration the varactor or varicap diode acts like a capacitor with the depletion region being the insulating dielectric and the capacitor plates formed by the extent of the conduction regions. The capacitance can be varied by changing the bias on the diode as this will vary the width of the depletion region which will accordingly change the capacitance. See related articles list in left hand margin.
•Zener diode: The Zener diode is a very useful type of diode as it provides a stable reference voltage. As a result it is used in vast quantities. It is run under reverse bias conditions and it is found that when a certain voltage is reached it breaks down. If the current is limited through a resistor, it enables a stable voltage to be produced. This type of diode is therefore widely used to provide a reference voltage in power supplies. Two types of reverse breakdown are apparent in these diodes: Zener breakdown and Impact Ionisation. However the name Zener diode is used for the reference diodes regardless of the form of breakdown that is employed. See related articles list in left hand margin.

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Gateway 2100 repaired

I felt it was time to post another case history.

Gateway 2100 LCD monitor, the monitor would turn on screen would flicker and then go black. After opening the monitor I found 1 capacitor, 47uF @16V with an ESR of 10 ohms(obviously bad) in the secondary side of the SMPS section of the SMPS/Inverter board. Looking at the inverter section I noticed two puffed and vented electrolytic capacitors both 220uF @16V, locations C301 and C302 that were obviously bad as well. Sorry but I did not record the location of the 47uF capacitor, but you can see where all the capacitors were located in the photos. I also noticed some darkened spots on the component side of the PCB, on the other side, the solder side of the PCB you could see that where the dark spots were is where the inverter circuit MOSFETs were located, U301, U302, U304 and U305.After testing the MOSFETs for shorts between gate to drain and gate to source to my surprise they tested good, but they did have major solder connection problems, the solder on their connections had completely broken down from heat. I re-soldered all the connections and replaced all the bad electrolytic capacitors and checked for any other problems with the monitor. After putting the monitor back together hooking up signal and turning it on, it worked like new.









If you are wondering why the transistors are identified with a U instead of a Q, as normally transistors are labeled with a Q and ICs are labeled with a U, well this is the case on some PCBs the designers will label transistor locations with U instead of Q and instead of labeling ICs as U they will just print IC.

Mail in repair service:
We offer mail in repair service on LCD monitors. We do the repair on the PSU/inverter board from the monitor in this post for $75.00 plus return shipping and handling. Click here to see our mail in repair service page for more information.

Different types of capacitors and their uses

Electronic capacitors are one of the most widely used electronic components. These electronic capacitors only allow alternating or changing signals to pass through them, and as a result they find applications in many different areas of electronic circuit design. There are a wide variety of types of capacitor including electrolytic, ceramic, tantalum, plastic, sliver mica, and many more. Each capacitor type has its own advantages and disadvantages can be used in different applications.

The choice of the correct capacitor type can have a major impact on any circuit. The differences between the different types of capacitor can mean that the circuit may not work correctly if the correct type of capacitor is not used. Accordingly a summary of the different types of capacitor is given below, and further descriptions of a variety of capacitor types can be reached through the related articles menu on the left hand side of the page below the main menu.



Capacitor construction
In essence the construction of an electronic capacitor is very simple, although in practice a lot of research and development has been put into capacitor technology. The basic electronics components consist of two plates that are insulated from one another. In between them there is an insulating medium known as the dielectric. The value of the electronic capacitor is dependent upon the area of the plates, the distance between them and the dielectric constant of the material or dielectric between them. The greater the area of the plates, the closer they are together and the greater the value of the dielectric constant the greater the value of capacitance.

Today, electronic capacitors are able to provide relatively high levels of capacitance within components that occupy a small volume. This is achieved in a number of ways. One is to have several sets of plates, and another is to place the plates very close to one another, having a thin layer of dielectric placed between them. In addition to this special insulating dielectric materials have been developed to enable high levels of capacitance to be achieved.

The method of construction of these electronic components is also important. In some capacitors the plates may be flat, and normally these capacitors will have rectangular, or more exactly cuboid shapes. Some will be tubular and in these capacitors the plates will be wound round on each other. The reasons for these types of construction are normally dependent upon the way in which the capacitors must be manufactured. The final stage in the construction of an electronic capacitor is to place it in a protective casing. In some instances it may be dipped in an insulating coating, in others it may be contained within a metal can.

Some capacitors types are what are termed polar or polarized. When this is the case the electronic capacitor has a positive and a negative connection and it must be placed in circuit so that the voltage across it is in a particular sense. If the voltage is incorrectly placed across the component then it may be damaged. Fortunately many capacitors, and in particular low value ones are non-polar and can be placed in circuit either way round.

Although there is a large variety that are available the most commonly used are ceramic, plastic film types, electrolytic and tantalum. These names refer to the type of dielectric that is used within the capacitor.

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Different types of resistors

Resistor Types:

Resistors (R), are the most commonly used of all electronic components, to the point where they are almost taken for granted. There are many different resistor types available with their principal job being to "resist" the flow of current through an electrical circuit, or to act as voltage droppers or voltage dividers. They are "Passive Devices", that is they contain no source of power or amplification but only attenuate or reduce the voltage signal passing through them. When used in DC circuits the voltage drop produced is measured across their terminals as the circuit current flows through them while in AC circuits the voltage and current are both in-phase producing 0o phase shift.

Resistors produce a voltage drop across themselves when an electrical current flows through them because they obey Ohm's Law, and different values of resistance produces different values of current or voltage. This can be very useful in Electronic circuits by controlling or reducing either the current flow or voltage produced across them. There are many different Resistor Types and they are produced in a variety of forms because their particular characteristics and accuracy suit certain areas of application, such as High Stability, High Voltage, High Current etc, or are used as general purpose resistors where their characteristics are less of a problem. Some of the common characteristics associated with the humble resistor are; Temperature Coefficient, Voltage Coefficient, Noise, Frequency Response, Power as well as Temperature Rating, Physical Size and Reliability.

In all Electrical and Electronic circuit diagrams and schematics, the most commonly used resistor symbol is that of a "zig-zag" type line with the value of its resistance given in Ohms, Ω

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Testing Silicon Controlled Rectifiers (SCR)

Here is a wonderful article written by my good friend Jestine Yong.


Testing SCR (silicon controlled rectifier) can be done by using an analog multi meter or specialize tester (such as the Peak electronic atlas component analyzer) designed to check semiconductor devices easily. SCR can be found in many electronic circuits. Part numbers such as the FOR3G and MCR 100-6 were very common used in computer monitor. Some called SCR as thyristor but in actual fact the word thyristor should not be associated exclusively with the silicon controlled rectifier. It is in fact a general name given to all four layer PNPN devices including the commonly used SCR. The diac, the Triac, and the SCS are the other popular devices belonging to the family of thyristors.

SCR consists of three pin of Gate (G), Anode (A) and Cathode (C). In order to identify the pin out, one must find it from semiconductor data book such the famous Philips ECG master semiconductor replacement guide. The data book will list out the general specification of the SCR such as the volt and ampere. If you want to know more details about a particular SCR, you can always try to search from the internet. Usually the SCR manufacturers will provide the full datasheet for those who want it.

Once you know the pin outs of the G, A and C legs you can begin to test the SCR. If you have the Peak electronic atlas component analyzer tester, what you need to do is to connect the three small clips to each pin of the SCR (any part number will do). The tester will begin to analyze the SCR and prompt you with the display such as "Sensitive or low power thyristor" before it tells you the exact pin outs of G, A and C. After the first test, the tester will eventually show you the answer at the LCD display. Red is Gate, Green is Cathode and Blue is Anode. It is a simple process and you will know the answer in less than 10 seconds. If there is a problem in the SCR, the tester would not be able to show the results instead it shows a shorted reading.

If you don't have this tester for checking SCR, I'm showing you another easy way on how to test SCR fast. You need an analog meter set to X1 ohm. Place the red probe to the Cathode and black probe to the Anode pin. At this time the meter doesn't show any reading. Now gently move the black probe and touch the Gate pin (the black probe still touching the Anode pin) and you will notice the meter's pointer will kick as shown at the picture (low resistance).

Removing the black probe from the GATE pin (the black probe still touching the Anode pin) you would noticed that the resistance continues to be there (low resistance). This is due to the conduction of SCR as the meter battery is usually able to supply current more than the holding current. If at this stage you removed the black probe from the Anode pin and connect it back, the pointer will dropped back to infinity (high resistance). If the SCR could hold the resistance then the SCR is considered good. If it can't hold then the SCR is faulty.

Conclusion- Practice testing SCR more often to see how's the result like. Try some different part numbers and power SCR-and if the resistance don't hold using X1 ohm, you may try X10 ohm and etc.

Jestine Yong is a electronic repairer and a writer, for more information how you can test electronic components like a professional please visit his website by clicking here.

See original article at ezine by clicking here.

The Silicon-Controlled Rectifier (SCR)

SCR schematic symbol.



Shockley(no not schottky) diodes are curious devices, but rather limited in application. Their usefulness may be expanded, however, by equipping them with another means of latching. In doing so, each becomes true amplifying devices (if only in an on/off mode), and we refer to these as silicon-controlled rectifiers, or SCRs.

The progression from Shockley diode to SCR is achieved with one small addition, actually nothing more than a third wire connection to the existing PNPN structure.

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