Types of Diodes AIM- To study the different type of Diodes.
Apparatus – Various types of diode
INTRODUCTION- Germanium point contact diode P.N junctions diode is formed by combining switch with an N- type S.C the PN junction so formed exhibits the increases in an equal properties of offer in allow resistance to current flow in one direction the P-n junction rectifying characteristics as a vacuum diode and is widely used as the detector in electronic circuit. Including radio and T.V receivers.
A P.N junction can be formed simply putting together a p type and N- type semiconductors the construction of PN junction diode in involves specially manufacturing technique of various type in one method a single crystal is ground from a melt which content sufficient quantities to that of material ground they after is change this is the ground junction diode in the second method a small induction in fuse on a water of N type generation figure shows the as a small signal dives in radio T.V and tape recorder and other electric circuit.
In the circuit symbol the terminal marked anode is connected to the P- type material while that marked cathode is connected to N- type material the arrow need also indicates the of direction conventional current flow in the usually marked by a circular band or action.
Zener diode-: Zener diode are is diodes which down voltage show the typical current voltage characteristic of zener diode behave like a closed switch and the forward current increase the diodes reverse bias a small reverse current flow of remains practically constant with an increase at reverse bias till the zener voltage is reached when this happened the reverse the reverse current opportunities increases to a very high value as a result of a the covalent bond near the junction beak down and releasing a large number of electron hole pairs of in the forms of a vlance break down zener diode are widely used in electronic circuit as voltage regulator and voltage reference standard when the avalanche current flows voltage across the diode remain constant.
Tunnel diode - : A Tunnel diode is a p-n junction device which difference from the junction diode and zener diode in the since that it has high percentage of impurities in its S.C element as result of heavily doping the charge carriers are able to a pass through the deflection layer near the junction by a process called tunneling the device permits both forward and reverse current with the very important feature that it present a –VE resistance region for a specific range of forward voltage in this characteristic of –VE resistance tunnel diode are used as amplifier and oscillator practically at low microwave frequency no avoid radiation effects effects the circuit symbols of tunnel diode is given in figure.
Varactor diode -: A reverse bias diode function be haves like a capacitor because the reverse bias keeps the charger depended away from the capacitor at the junction can controlled by the reverse bias applied to the diode which makes the deflection zone wider or narrow as the reverse bias is varied such a voltage sensitivity a capacitance is called a varactor as time frequency controlled the circuit involve for a varactor is given in the figure.
Varistor diode -: A varasistor consist of two junction diode at opposite polarities connected as show in its circuit symbol in figure varistor is generally used as shunt across the collector in circuit as operation against sudden jump of voltage either of –VE of –VE nature.
L.E.D. -: light emitting diode. P-N junction are made up of certain special material like gallium compounds emit light as result of energy release by the recombination of charge radiation of red, green, yellow, light are emitted when a forward bias the order 1.2v is applied from special types of cell L.E.D units are arranged in segments which area find extensive used in electronic watch and marry electronic meeting devices fig. shows circuit symbol of L.E.D
P-N junction photo Diode -: It is two terminal device which is operated by first reverse biasing the junction and thus illuminative at reverse. Bias P-N junction as a small amount of reverse saturation current is due to the generated electron hole pairs in this , is in range on the No- these minority carries depending the intensity of light incident on the junction when the diode is in a glass package light can reach junction and thus changes the reverse currents.
The basic biasing arrangement construction and symbol of photo diode shown in fig- as soon as hence has been used light up the reverse biased junction.
The active diameter of this device about 2.5 mm but they are mounted instant are to by package with a window to allow may incident light.
The characteristics of figure shown that for given reverse voltage it is increase in the level of illumination the level reverse current can be changed in this way reverse resistance of the diode can be charge by a factor of nearly 20.
A photo diode can turns its current ON /Off at minimum rate applied of a photo diode include.
1) Both visible and invisible. [ De modulation ]
2) Switching.
3) Circuit that required stability and high speed.