Electronic resistors are passive components that limit the flow of electric current in a circuit. They are fundamental to various electronic devices and circuits, playing a critical role in controlling voltage and current levels.
Basic Principles of Resistors
Ohm’s Law
Resistors operate based on Ohm’s Law, which states that the current (I) flowing through a resistor is directly proportional to the voltage (V) across it and inversely proportional to the resistance (R).
Resistance is always equal to your voltage divided by the current or R = V/I. You can also say that your voltage is equal to your current multiplied by your resistance, or V = I x R in equation form
Resistance
The resistance of a resistor is measured in ohms (Ω). It quantifies how strongly the resistor opposes the flow of electric current.
Types of Resistors
Resistors come in various types, each suited for specific applications:
Fixed Resistors: These resistors have a constant resistance value and are the most common type. They are typically made from carbon composition, metal film, or wire wound.
Variable Resistors: Also known as potentiometers or rheostats, these allow the resistance to be adjusted manually or electronically.
Specialty Resistors
Thermistors: Temperature-sensitive resistors that change resistance with temperature.
Photoresistors (LDRs): Change resistance based on light intensity.
Metal Oxide Varistors (MOVs): Protect circuits from voltage spikes by changing resistance with voltage.
Characteristics
Power Rating: Resistors are rated for the maximum power they can dissipate without damage, typically measured in watts (W). Exceeding this rating can cause overheating and failure.
Tolerance: This indicates how much the actual resistance can vary from the stated value, expressed as a percentage. Common tolerances include ±1%, ±5%, and ±10%.
Temperature Coefficient: This measures how much a resistor’s value changes with temperature. It is often specified in parts per million per degree Celsius (ppm/°C).
Noise: Resistors can generate electrical noise, which may affect sensitive circuits. This is particularly important in audio and radio frequency applications.
| Color | 1st band | 2nd band | 3rd band |
|---|---|---|---|
| Black | 0 | 0 | 0 |
| Brown | 1 | 1 | 1 |
| Red | 2 | 2 | 2 |
| Orange | 3 | 3 | 3 |
| Yellow | 4 | 4 | 4 |
| Green | 5 | 5 | 5 |
| Blue | 6 | 6 | 6 |
| Violet | 7 | 7 | 7 |
| Gray | 8 | 8 | 8 |
| White | 9 | 9 | 9 |
| Color | Multiplier | Tolerance | Temp. Coefficient |
|---|---|---|---|
| Black | x 1 Ω | ||
| Brown | x 10 Ω | ± 1% | 100ppm |
| Red | x 100 Ω | ± 2% | 50ppm |
| Orange | x 1K Ω | 15ppm | |
| Yellow | x 10K Ω | 25ppm | |
| Green | x 1000K Ω | ± 0.5% | |
| Blue | x 1M Ω | ± 0.25% | |
| Violet | x 10M Ω | ± 0.1% | |
| Grey | ± 0.05% | ||
| White | |||
| Gold | x 0.1 Ω | ± 5% | |
| Silver | x 0.01 Ω | ± 10% |
Applications
Voltage Division: Resistors can be used in voltage divider circuits to produce a specific output voltage from a larger input voltage.
Current Limiting: They protect sensitive components by limiting the amount of current that can flow through them.
Biasing: In transistor circuits, resistors are often used to set the operating point, or bias, of the transistor.
Signal Processing: They are used in filters, oscillators, and various analog circuit designs to shape and control signals.
Pull-up and Pull-down: Resistors are used in digital circuits to ensure that inputs to logic gates settle at expected logic levels when no active device is driving the line.
Using Resistors with LEDs
LEDs (light emitting diodes), are semiconductors that convert electricity into light, such as blinking lights on a circuit board. a LED usually has to have a resistor in the circuit to limit the amount of current flowing through the LED. To determine the correct resistor to use with a LED, you ned to calculate the resistance value based on the supply voltage, the voltage drop across the diode, and the desired current (from LED’s spec sheet), using the formula R = (supply voltage – diode’s voltage drop)/ desired current. essentially, the resistor is chosen to limit the current flowing through the diode to a safe level.
Conclusion
These electronic components are essential components in virtually all electronic circuits. Their ability to control and manage current flow makes them crucial for circuit design, enabling engineers to create functional, reliable electronic devices across a wide range of applications.