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

varactor diode

A varicap diode is a type of diode which has a variable capacitance that is a function of the voltage impressed on its terminals

Varactors are operated reverse-biased so no current flows, but since the thickness of the depletion zone varies with the applied bias voltage, the capacitance of the diode

 

can be made to vary. Generally, the depletion region thickness is proportional to the square root of the applied voltage; and capacitance is inversely proportional to the depletion region thickness. Thus, the capacitance is inversely proportional to the square root of applied voltage.

varicap diodes are a particularly useful form of semiconductor diode. Finding uses in many applications where electronically controlled tuning of resonant circuits is required, for items such as oscillators and filters

Diode bridge

There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is one of them and it is available in special packages containing the four diodes required. Bridge rectifiers are rated by their maximum current and maximum reverse voltage. They have four leads or terminals: the two DC outputs are labelled + and -, the two AC inputs are labelled

The diagram shows the operation of a bridge rectifier as it converts AC to DC. Notice how alternate pairs of diodes conduct

Tunnel diodes

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

SCHOTKKY DIODES

This type of diode is ideally suited for low voltage, high frequency rectification, or as a free wheeling and polarity protection diode.

This diode employs the Schottky Barrier principle with barrier metal that produces optimal forward voltage drop-reverse current tradeoff.

These diodes looks similar to the standard rectifier diode, so CARE SHOULD BE TAKEN when you are inserting these diodes, ALWAYS READ the part number written on the face of the component to be sure that the part you are inserting is the real one.

The Schottky Diode is best used for high frequency rectification commonly used in Switched Mode Power Supplies (SMPS)

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 photodetectors. See related articles list in left hand margin

Light Emitting Diode : LED

LEDs are so popular in electronics. They are used in many applications from toys, flashlights, computer peripherals, digital cameras, cellphones, etc.

My first electronic circuit was to light an LED and sadly It was destroyed because of high voltage. That was before, but now I know how these little things work and I'm enjoying every thing about it.

The figure on the left(top) is the schematic diagram representation on an LED.

LEDs comes in various colors the photo on the left(bottom) shows three different colors of leds. The clear LED can be thought of as a white LED, infact it's just casing. The clear LED can have other variations of color like bright red, blue, bright green.

The clear/transparent LEDs gives a much brighter intensity of light that it emits.

The color that an LED emits depends on the gas used inside it

Zener diode

Zener diode is a type of diode that permits current in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage"

A reverse-biased Zener diode will exhibit a controlled breakdown and allow the current to keep the voltage across the Zener diode at the Zener voltage. For example, a diode with a Zener breakdown voltage of 5.1 V will exhibit a voltage drop of 5.1 V if reverse bias voltage applied across it is more than its Zener voltage. However, the current is not unlimited, so the Zener diode is typically used to generate a reference voltage for an amplifier stage, or as a voltage stabilizer for low-current applications

Zener Diode Voltage Regulator Circuit

A zener diode can be used to make a simple voltage regulation circuit as pictured above. The output voltage is fixed at the zener voltage of the zener diode used and so can be used to power devices requiring a fixed voltage

Diodes

A diode is an electrical device allowing current to move through it in one direction with far greater ease than in the other. The most common type of diode in modern circuit design is the semiconductor diode, although other diode technologies exist. Semiconductor diodes are symbolized in schematic diagrams as such

Permitted direction of electron flow


When placed in a simple battery-lamp circuit, the diode will either allow or prevent current through the lamp, depending on the polarity of the applied voltag

Current permitted -Diode is forward-biased

Current prohibited -Diode is reverse-biased

When the polarity of the battery is such that electrons are allowed to flow through the diode, the diode is said to be forward-biased. Conversely, when the battery is "backward" and the diode blocks current, the diode is said to be reverse-biased. A diode may be thought of as a kind of switch: "closed" when forward-biased and "open" when reverse-biased

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 equal for a wide range of diode currents, meaning that diode voltage drop not like that of a resistor or even a normal (closed) switch. For most purposes of circuit analysis, it may be assumed that the voltage drop across a conducting diode remains constant at the nominal figure and is not related to the amount of current going through it.


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

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.


REVIEW:

A diode is an electrical component acting as a one-way valve for current.

When voltage is applied across a diode in such a way that the diode allows current, the diode is said to be forward-biased.

When voltage is applied across a diode in such a way that the diode prohibits current, the diode is said to be reverse-biased.

The voltage dropped across a conducting, forward-biased diode is called the forward voltage.
Forward voltage for a diode varies only slightly for changes in forward current and temperature, and is fixed principally by the chemical composition of the P-N junction.

Silicon diodes have a forward voltage of approximately 0.7 volts.

Germanium diodes have a forward voltage of approximately 0.3 volts.

The maximum reverse-bias voltage that a diode can withstand without "breaking down" is called the Peak Inverse Voltage, or PIV rating