Write down the symbol and truth table for OR gate

The symbol for the OR gate is shown above. The truth table for the OR gate is as follows A B Y=A+B 0 0 0 0 1 1 1 0 1 1 1 1

What are the majority and minority carriers in a p-type semiconductors

Charge Carriers in p-type Semiconductors: In the p-type semiconductor, the number of holes are completely dominated by the number of acceptor sites. Therefore, the total number of holes is approximately equal to the number of donor sites, Charge neutrality of this semiconductor material is also maintained. The net result is that the number of holes is increased, while the number of conduction electrons is reduced. The imbalance of the carrier concentration in the respective bands is expressed by the different absolute number of electrons and holes. Holes are majority carriers, while electrons are minority carriers in p-type material.

Draw the V - I characteristic curve for forward and reverse bias p-n junction diode ( graph paper not required)

The V-I characteristic of a p-n junction diode in forward bias and reverse bias is given above

What is Zener diode? Explain with a circuit diagram, how a Zener diode regulates the voltage across a load resistance

A Zener diode is a heavily doped silicon semiconductor device that permits current to flow in either a forward or reverse direction. The diode consists of a special, heavily doped p-n junction, designed to conduct in the reverse direction when a certain specified voltage is reached called Zener voltage. It is a diode in which at a critical reverse voltage a large reverse current can flow. Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. When connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. A Zener diode is connected as shown. The output voltage is taken across a load resistance R L . When the input d.c across the diode increases beyond the breakdown voltage, the current through the circuit rises sharply, causing a sufficient increase in voltage drop across load resistance R L . As a result of it, the voltage across the Zener diode remains constant and the output voltage lowers back to normal. When the input d.c. voltage across Zener diode decreases, the current through the circuit goes down sharply causing a sufficient decrease in the voltage across dropping resistance, hence the output voltage across the resistor is raised to normal. Thus, the output voltage remains constant.

Explain with a circuit diagram the action of a transistor as a switch.

A switch is a device which can turn ON and OFF current is an electrical circuit. The circuit for use of a transistor as a switch is shown below: V BB and V CC are two dc supplies which bias base-emitter and emitter collector junctions respectively. Let V BB be the input supply voltage. This is also input dc voltage V C The dc output voltage is taken across collector-emitter terminals, R L is the load resistance in the output circuit. The output characteristic curve is shown below: When the transistor is non-conducting I C = 0 , it is said to be ‘switched off’ but when it is conducting I C ≠ 0 ; it is said to be ‘switched ON. As long as the input voltage V i is low and unable to overcome the barrier voltage of the emitter base junction, V o is high ( I C = 0 and V o = V CC ), so the transistor is ‘switched OFF’ and if it is high enough to derive the transistor into saturation I C ( is high and so V 0 = V CC - I C R L is low, very near to zero, so the transistor is ‘switched ON’. Thus we can say low input switches the transistor is OFF state and high input switches it ON. The switching circuits are designed in such a way that the transistor does not remain in active state.