Designing of OR gate using transistor

 Ans-:

1.     Introduction-:

 

OR gate gives high at the output when either of the inputs is high or both the inputs are high, otherwise it gives low

INPUT 2 B	OUTPUT A+B
0	0
1	1
0	1
1	1

 Component Required-:

Ø  Two 4.7k resistor

ؠؠTwo toggle switches

ؠؠGeneral purpose LED

ؠؠ5V power supply

ؠؠSome jumper wires

ؠؠBreadboard

ؠؠMultimeter

WORKING OF OR GATE USING TRANSISTOR-:

The transistors are connected in parallel and their bases are used as input. The base of both the transistors act like input and one of the emitters of both the transistors is used to derive the output. Initially, both the switches are in OFF state so none of the transistor bases is getting a power supply. The base to emitter junction and base to collector junction of both the transistors have a voltage lower than 0.65V, which is the practical threshold voltage of the diode. Both junctions are in reverse bias hence both the transistors turn OFF and go into their cutoff state. Therefore the transistors act like an open switch. Since all the current coming from the collector through resistor R4 is blocked by the transistor hence we get a low voltage at the output, which turns off the LED.

In next case when we close the switch 1 then the base of the first transistor is getting a positive value of voltage. The base to emitter junction and base to collector junction of the first transistor have a voltage greater than threshold voltage so both junction are in forward bias. The first transistor reaches into saturation state and act like a short circuit whereas the second transistor is still in the cutoff state due to no power supply base. Hence all current passes through the first transistor to the output and our LED lights up.

Likewise, if we open switch 1 and close switch 2 then the first transistor goes in cutoff while the second transistor in saturation. Now current flows through the second transistor and we get high at the output.

When we close both switches, the junction of both the transistors has a voltage greater than threshold voltage so both junctions are in forward bias. Therefore both transistors are in saturation state and act like a short circuit. The current now gets a short circuit path and flows from both of the transistors which derive high at the output, thereby lighting up the LED.

We can say for OR logic, the transistor is connected in parallel and either of the transistors must be in its conducting state to derive high at the output. If one or both the inputs have high value then at the output we get high, otherwise low.

 

CONCLUSION-:

The function of OR gate is to find the maximum between the inputs which are binary in nature. It is one of the  basic gates used in Boolean algebra and electronic circuit  like transistor- transistor logic and complementary metal oxide semiconductor makes one of it.