Transistors, Amplifiers, and Electronic Components

Transistors

Transistors
NPN and PNP transistors function as amplifiers or switches. They are used to amplify, control, and stabilize electrical signals. There are two main types: Bipolar and Single pole. Transistors are formed of P-type and N-type materials. The three legs are: emitter, base, and collector.

Operation of an NPN Transistor

If the base-emitter junction is forward biased, the transistor works in the active region. Electrons from the emitter are repelled by the negative pole and move towards the positive pole. When they reach the base, some are attracted, forming the base current (IB). The rest are attracted to the positive collector, forming the collector current (IC). The emitter current (IE) is the sum of the base and collector currents: IE = IB + IC.

The internal resistance of a transistor is a function of the input signal. Transistors regulate the flow through a circuit.

Darlington Pair

Darlington Pair
This configuration amplifies voltage. It is used when a single transistor is not sufficient to achieve the desired amplification.

Coils

Coils
These components are used when a magnetic field needs to be created (e.g., in a clock). Their behavior depends on whether the current is direct or alternating.

Step DC to AC

Step DC to AC
A simple power supply has three stages:

Processing

Using a transformer, the values of voltage and current can be changed without altering the shape of the alternating wave. The power remains the same. The input is modified between the first and second output.

Rectification

Alternating current (AC) is converted into pulsating current using diodes, typically a diode bridge. This lowers the wavelength.

Filtering

A capacitor connected in parallel with the output reduces the ripple wave, resulting in a nearly constant voltage wave.

Stabilization

This involves placing a reverse-biased Zener diode to minimize the output waveform of the rectifier and obtain direct current (DC). If the electronic device requires a very stable voltage, a voltage regulator is added. This regulator replaces the Zener diode and provides a constant output voltage, even if the charging current or network voltage varies. The sequence is: 1st input voltage, 2nd output voltage, and 3rd common.

Operational Amplifier

Operational Amplifier
This integrated circuit includes a differential amplifier with two inputs in phase opposition. With them, we can achieve large voltage gain. It has three stages:

1. Differential amplifier (AD) expanded with a difference in input voltage.
2. Voltage gain.
3. Low output impedance.

Capacitors

Capacitors
Capacitors can store electric charge and use it later. Capacity is the ratio between the electric charge stored by a capacitor and the voltage at which it is measured, in farads. The formula is: C = q / V