How does a transistor amplify current?

How does a transistor amplify current?

Meaning of Transistor & Amplification

Transistor is electronic solid state semiconductor device which regulates electric current flow and acts as a switch or gate for electronic signals. A transistor consists of three layers of a semiconductor material. Those layers are capable of carrying a current. Transistors are devices that can amplify a signal in a circuit. It is normally made of germanium or silicon layers. A transistor requires very little current to operate so, releases very little heat. However, heat also depends upon it configuration. It is used in different things, such as an amplifier, oscillator, rectifier, switch, etc.

Similarly, Amplification is the process of increasing the strength of a SIGNAL. A signal is just a general term used to refer to any particular current, voltage, or power in a circuit. .amplification is the process of increasing the magnitude of a variable quantity, especially the magnitude of voltage, power, or current, without altering any other quality.Amplification is a ratio between two values which does not imply that the output value is greater than the input value.

Transistor amplifying current

Transistors are normally used as amplifiers. Some transistor circuits are current amplifiers, with a small load resistance, other circuits are designed for voltage amplification and have a high load resistance and others amplify power.

Considering the above diagram:

The small current travels from the voltage source into the base of the transistor. A current at the base turns on the transistor. The current is then amplified and travels from the emitter of the transistor to the collector. The amplified current is large enough to turn on and light the LED.A separate power source must be connected to the collector of the transistor because a transistor is an active device, which means it needs power in order to operate.

The amplifier is complex circuit which is exploiting properties of a transistor. It has input node and output node.The output voltage from the amplifier, taken at the collector of Q1 with respect to the emitter, is a negative alternation of voltage that is larger than the input, but has the same sine wave characteristics. During the negative alternation of the input signal, the transistor current increases because the input voltage aids the forward bias.The output for the negative alternation of the input is a positive alternation of voltage that is larger than the input but has the same sine wave characteristics.The direct current flowing through the circuit develops more than just base bias; it also develops the collector voltage (VC) as it flows through Q1 and RL. Thus, the output is a negative alternation of voltage that varies at the same rate as the sine wave input, but it is opposite in polarity and has a much larger amplitude.This permits the collector voltage (VC) to change with an input signal, which in turn allows the transistor to amplify voltage. That is enough voltage on the base, along with ground on the emitter and the large positive voltage on the collector, to properly bias the transistor.This action results in a positive output voltage, which has the same characteristics as the input except that it has been amplified and the polarity is reversed. The input signals in the preceding circuits were amplified because the small change in base current caused a large change in collector current. And, by placing resistor RL in series with the collector, voltage amplification can be gained.

Connecting a Transistor in a Circuit for Amplification:

Experiment with LED

Transistor circuit for amplification

The ciruit to light an LED where the current in the circuit is 40µA, which is not enough to light an LED. In this condition if we place a transistor in the circuit, which has a gain of 100, the signal will be boosted

from 40µA

to

40x100=4mA.

This current will now be sufficient to light our LED in the circuit.

References:

https://www.youtube.com/watch?v=W8hqr5X5ii0

https://www.youtube.com/watch?v=uo2KgRN04XI

https://www.youtube.com/watch?v=XT0M6e1PGcg

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Transistor amplifying current

Connecting a Transistor in a Circuit for Amplification:

Experiment with LED