Passive and Active Electronic Components: A Comprehensive Guide
Unit 4: Building Blocks
1. Passive Components
Passive components transmit active electrical signals and provide links between them.
1.1. Resistance
These electrical components, made of ceramic or iron, produce voltage drops or reduce the current consumed by a load. Their resistance value, measured in ohms, depends on the color code painted on the exterior. The power they can dissipate (without burning) depends on their size.
Linear Resistors
Their resistance value is constant and predetermined by the manufacturer.
- Applications:
- Two-speed electro-fans
- Voltage reduction to 12V
Variable Resistors
Their resistance value can vary within limits. A third terminal connected to a movable contact slides over the resistive element, providing resistance variation. This third terminal can be displaced or rotated.
Potentiometer
A potentiometer is a resistor with a sliding cursor that divides it into two resistors with a constant sum. Its value can be adjusted between the cursor pin and one end. Varying the cursor position changes the output voltage.
- Applications:
- Fuel flow regulation
- Picture brightness control
Thermistor
Thermistors are resistors that vary significantly with temperature.
- PTC (Positive Temperature Coefficient): Resistance increases with increasing temperature. Applications include diesel engine preheating plugs, heating tube locks.
- NTC (Negative Temperature Coefficient): Resistance decreases with increasing temperature. Applications include engine temperature and outside air suction temperature measurement.
- VDR (Voltage Dependent Resistor): Resistance decreases with increasing applied voltage. Used to suppress voltage surges (e.g., in drills).
- LDR (Light Dependent Resistor): Resistance decreases with increasing light intensity.
1.2. Inductors
Inductors create stronger magnetic fields than a single conductor. They form a loop or multiple loops (coil), often with a ferromagnetic core to increase inductance.
Transformer
Transformers transport energy or change voltage and current levels between circuits. They consist of a closed iron core with two coils (primary and secondary) with different numbers of turns.
1.3. Capacitor
A capacitor is an open circuit that stores electric charge when voltage increases (charging) and releases it when voltage decreases (discharging). Its capacitance, measured in Farads, is proportional to the voltage.
1.4. Relay
A relay is an electromechanical switch controlled by an electric circuit. A coil and electromagnet activate one or more contacts that open or close other independent electrical circuits. It allows control of high voltage or high power circuits with small control voltages.
2. Active Components
2.4. Diode
A diode is a semiconductor device that allows current flow in only one direction, similar to a switch. Its characteristic curve has two regions: below a certain voltage, it behaves like an open circuit; above it, like a closed circuit with low resistance. Diodes are often called rectifiers because they suppress the negative part of a signal, a first step in converting AC to DC.
Zener Diode
A special diode always used in reverse bias. In forward bias, it behaves like a regular diode; in reverse bias, it maintains a constant voltage.
Varicap
A variable capacitance diode that behaves like a capacitor with voltage.
Photodiode
A light-sensitive diode whose reverse saturation current increases with light intensity.
LED (Light Emitting Diode)
Emits light when forward biased. Brightness increases with current.
2.5. Transistor
A three-terminal semiconductor component that amplifies or switches electronic signals. A small current at the base controls a larger current between the collector and emitter. It can act as a switch (like a relay) or an amplifier.
- PNP: Emitter and collector are P-type, base is N-type.
- NPN: Emitter and collector are N-type, base is P-type.
Darlington Transistor
Two transistors combined. The emitter of the first transistor controls the base of the second, allowing a very small current to control a much larger one.