Essential Electronic Components and Circuit Functions

Resistors

Resistors slow down and restrict the flow of current. Resistance is measured in Ohms (Ω).

Types of Resistors

There are two main types: fixed and variable.

Variable Resistors

• Potentiometer / Rheostat: A type of resistor whose value can be modified by a movable piece. These can be used as volume controls on audio equipment or light dimmers.
• Thermistors: These are resistors that depend on temperature. There are two types:
  • NTC (Negative Temperature Coefficient): As temperature increases, resistance decreases.
  • PTC (Positive Temperature Coefficient): As temperature increases, resistance increases.
  • Used as temperature detectors in thermostats.
• LDR (Light Dependent Resistor): The resistance varies according to the amount of light the resistor receives. As light increases, resistance decreases. Used in cameras, photocopy machines, position sensors, street light control, night light control, etc.

Capacitors

Capacitors can store electric charge. The value of a capacitor, known as capacitance, is measured in Farads (F).

They can be split into two groups: polarized (electrolytic) and unpolarized. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed.

Semiconductors

Semiconductors are solid materials that, depending on environmental conditions, can act as conductors or as insulators.

• Intrinsic Semiconductors: Pure materials like Silicon (Si) and Germanium (Ge).
• Extrinsic Semiconductors: These contain doping elements. Under research: Carbon and Graphene (grafeno).

Diodes

A diode is formed by joining a P-type crystal (gaps) with an N-type crystal (electrons).

Transistors

Transistors are basic elements in electronic circuits, made from semiconductive materials. They have three leads (terminals): emitter, base, and collector. They operate by a small current flowing into the base and are used to amplify and switch electronic signals and electrical power.

Transistor Types

• Bipolar Junction Transistor (BJT)
• Field-Effect Transistor (FET)

Circuit Operation and Examples

If the circuit is open, there is no current in the base (Ib = 0). Transport is blocked (Ic = 0), and the light bulb remains off. If you close the circuit, there will be current in the base; the transistor will amplify the signal and the light bulb will be on.

In a two-transistor circuit: if the circuit is open (Ib1 = 0), T1 is blocked, which means Ib2 = 0 and T2 is blocked. Consequently, Ic2 = 0 and the bulb is off. If we close the circuit, T1 enters amplification mode, which triggers T2 to amplify as well, turning the light bulb on.

Switch and Capacitor Interaction

When the push button is open, there is no current in the base (transistor blocked) and the capacitor has no charge. If we close the circuit, the transistor will work as an amplifier, the bulb will be on, and the capacitor will charge. When we open the circuit again, the bulb will continue lighting because the capacitor will provide electricity to the base of the transistor.