To choose the right resistor, you need to determine the required resistance value (using Ohm’s Law: R = V/I), the power dissipation (P = V*I), and the desired tolerance.
Here’s a breakdown of the process:
1. Determine the Required Resistance:
Ohm’s Law:
The fundamental equation for calculating resistance is R = V/I, where:
R = Resistance (in Ohms)
V = Voltage (in Volts)
I = Current (in Amps)
Example:
If you need 5 volts across a component and the component draws 0.1 amps (100mA), then the required resistance is R = 5V / 0.1A = 50 Ohms.
2. Calculate Power Dissipation:
Power Formula:
The power dissipated by a resistor is calculated as P = V*I, where:
P = Power (in Watts)
V = Voltage (in Volts)
I = Current (in Amps)
Example (using the previous example):
If the resistor has 5 volts across it and 0.1 amps flowing through it, the power dissipated is P = 5V * 0.1A = 0.5 Watts.
Safety Margin:
Always choose a resistor with a power rating higher than the calculated power dissipation to prevent overheating and ensure reliability. A common practice is to use a resistor with a power rating at least double the calculated power.
