Mutchus

Opto Coupler Opto coupler is a solid state component in which light emitter the light path and light detector are all enclosed within the component and cannot be altered externally. Usually infrared emitting diode (IRED) can be used as a light emitter. Photo transistor can be used as a light detector. Principle: Here is one way transistor of electrical signal from LED (IRED) to photo transistor without any electrical connection between the input and output circuitry. The degree foe solation between input and output depends on the kind of material used in the light path and on the distance between the light emitter and signal light detector. If the distance between emitter and detector is greater, then the isolation is better but current transfer ratio of detector to emitter current is lower. Working: The fig shows the symbol of Opto coupler. The coupler may be operated as a switch in which cause both the LED and photo transistor are normally OFF. A pulse of current through the LED (IR...

Working of UJT 1. If voltage is applied at V BB with emitter open, a voltage gradient is established along the n-type bar. Since the emitter is located nearer to B 2 , more than half of V BB appears between the emitter and B 1 , the voltage V 1 between emitter and B 1 establishes a reverse bias on the pn junction and the emitter current is cutoff. 2. If a positive voltage is applied at the emitter, the pn junction will remain reverse biased so long as the input voltage is less than V 1 . If the input voltage to the emitter exceeds V 1 , the pn junction becomes forward biased. Under these conditions, holes are injected from p-type material in to the n-type bar. These holes are repelled by positive B 2 terminal and they are attracted towards B 1 terminal of the bar. This accumulation of holes in the emitter to B 1 region results in the decrease of resistance in this section of the bar. The result is that internal voltage drop from emitter to B 1 is decreased and hence the emitter curr...

Light Emitting Diode The LESD is basically a device which changes input electrical energy into output optical radiation in the visible or infrared position of spectrum depending on the semiconductor material used. LEDs have replaced incandesced lamp in many applications because of low voltage long life and fast on off switching. He materials used in manufacturing the LEDs are 1.        Gallium Arsenide Phosphide (GaAsP): It provides either red light or yellow light. 2.        Gallium Phosphide (GaP): It provides red or green light. 3.        Gallium Arsenide (GaAs): It provides infrared radiation Principle: When a P-N junction forward biased, charge carrier recombination take place at a junction as electron cross from the n- side and combine with holes on the p- side. Free electrons are in the conduction band of energy level while holes are in the valence band. Therefore electronics are at place ...

Depletion MOSFET Depletion MOSFET may be fabricated from the basic MOSFET structure. An n-type channel is obtained by diffusion between N + type source and drain in an n-channel MOSFET. The below figure shows the structure of depletion MOSFET.     n-channel Depletion MOSFET Working of Depletion MOSFET When the gate source voltage is zero considerable drain current flows. When the gate is applied with negative voltage. Positive charges are induced in the n-channel through the Si O 2 layer of the gate capacitor. The conduction in n-channel FET is due to electrons i.e. the majority carriers. Therefore the induced positive charges make the n-channel less conductive. The drain current therefore gets reduced with increase in the gate bias voltage. The distribution of charges in the channel results in depletion of majority carriers. That is why this type of FET is called depletion MOSFET. The voltage drop due to the drain current causes the channel region nearer to the drain more dep...

Photo transistor (Photo Duo Diode) A photo transistor is similarly to an ordinary bipolar junction transistor except that no base terminal is provided. Instead of base current the input to the transistor is provided in the form of light. Principle   Consider an ordinary transistor with its base terminal open circuited. The collector base leakage current I CBO will acts as base current. Since            I C = βI B + (1 + B) I CBO    And  I B = o since base is open circuited             I C = (1 + β) I CBO In photo transistor I CBO is increased when the collector base junction is illuminated. When I CBO is increased the collector current is also increased therefore for a given amount of illumination on a very small area of the photo transistor provides much largest output current. Therefore the photo transistor is a light detector which combines a photo diode ...