BJT LED Control Circuit

 BJT LED Control:



Description:

                     This circuit is used to control the current of an LED using a low power voltage source. 

By exploiting the current amplification of the BJT. The voltage source will only need to provide the base current instead of the LED current, which is beta times smaller.

Base current:

                     The Vbe voltage of the transistor sets at 0.7V as it consists of a pn junction, thus the voltage drop across R1 can be easily found, and the base current consequently.

Collector current:

                          This current is the results of the amplification of a Beta factor of the base current and sets the current flowing into the LED.

Max Collector current:

                                     The collector current still needs to be consistent with Ohm's law, which sets the maximum current that can flow in that branch, no matter how high the base current is. 

Vce(sat) is the voltage between collector and emitter when the BJT is in saturation.


QUESTION:

1)What is BJT and its working principle?

Answer:A Bipolar Junction Transistor (BJT) is a three-terminal device which consists of two pn-junctions formed by sandwiching either p-type or n-type semiconductor material between a pair of opposite type semiconductors. The primary function of BJT is to increase the strength of a weak signal, i.e., it acts as an amplifier

2)What is the main function of BJT?

Answer:As with all transistors, the basic function of a BJT is typically to function as a switch or to amplify, filter, and rectify power. Bipolar transistors are current-controlled and operated devices, meaning that a much smaller base current causes a larger current to flow from emitter to collector.

3)What are the two types of BJT?

Answer:A bipolar transistor (bipolar junction transistor: BJT) consists of three semiconductor regions forming two junctions. There are two types of structure: npn and pnp. Products with npn up to 800 V and pnp up to -600 V are available. In addition, there are also bias resistor built-in transistors (BRTs).

4)What are the advantages of BJT?

Answer:Advantages of BJT :

They have a better voltage gain.

They have a high current density.

They have a low forward voltage.

It can be operated in low to high power application.

BJT has a large gain bandwidth.

BJT shows better performance at high frequency.

5)What is meant by BJT?

Answer:A Bipolar Junction Transistor, or BJT, is a solid-state device in which the current flow between two terminals (the collector and the emitter) is controlled by the amount of current that flows through a third terminal (the base).

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