A voltage divider is an electrical circuit that converts a higher voltage into a lower one by using a pair of resistors (or sometimes other components). It divides the input voltage into smaller parts based on the ratio of the resistances.
Voltage Divider Calculation
In electronics the voltage divider is on of the simplest yet most widely used circuits. Whether you are biasing a transistor, reading a sensor with a microcontroller, or creating a reference voltage for an analog circuit, voltage dividers play a central role.
The operation of a voltage divider is based on Ohm's Law and the concept of series circuits. In series, current is the same through all components where the voltage across each resistor depends on its resistance value.
So, if current I flow through the series resistors: I = VIn / (R1 + R2)
The voltage across R2 (which is the output) is: VOut = I x R2
Substituting I: Vout = VIn x R2 / (R1 + R2)
This is the voltage divider formula which is tells you how much voltage develops across the second resistor.
Design Rules for Voltage Divider
Rule 1: Voltage divider should not drive heavy load. A major limitation is it cannot supply current to high-power loads. If you connect a load resistance RL across R2, it forms a parallel network.
RParallel = R2 x RL / (R2 + RL)
This changes the output voltage, often drastically.
Rule 2: Load resistance must be much higher. A good design rule RL ≥ 10 x R2. This ensures the voltage divider remains accurate.
Voltage Divider Practical Applications
Voltage dividers are found in almost every electronics circuit. Some major uses includes:
Sensor Interfacing: Many sensors change resistance with temperature, light, or pressure. Using a voltage divider, this resistance changes a voltage that can be measured.
ADC Scaling: Microcontroller Analog-to-Digital Converter (ADC) pins usually accept 0-3.3V to 0-5V. A voltage divider reduces higher signals to this safe range.
Biasing Transistor: BJT bias networks use two resistors as a voltage divider to set the base voltage.
Level Shifting: Use to shift 5V logic to 3.3V to microcontrollers.
Reference Voltage Generation: Op-ams and analog circuits need stable reference voltages.
Measuring High Voltages: Large resistors divide mains voltage (230V to millivolts) for safe measurement.
Potentiometers: A potentiometer is essentially a variable voltage divider.
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