Voltage Divider
A voltage divider is one of the most widely used resistor circuits in electronics. It uses two or more resistors connected in series to produce an output voltage that is a fraction of the input voltage. Voltage dividers are used in power supplies, analogue sensors, amplifier biasing, reference voltage generation, battery monitoring and countless other electronic circuits.
What Is a Voltage Divider?
A voltage divider consists of two or more resistors connected in series across a voltage source.
The output voltage is taken from the junction between two resistors. Since the resistors share the supply voltage, the junction provides a lower voltage than the source.
Basic Circuit
The simplest voltage divider uses two resistors.
Vin │ [R1] │──── Vout [R2] │ GND
Voltage Divider Formula
The output voltage depends on the resistor values.
VOUT = VIN × R2 ÷ (R1 + R2)
| Symbol | Meaning |
|---|---|
| VIN | Input voltage. |
| VOUT | Output voltage. |
| R1 | Upper resistor. |
| R2 | Lower resistor. |
Worked Example 1
Determine the output voltage using:
- VIN = 12 V
- R1 = 1 kΩ
- R2 = 1 kΩ
VOUT = 12 × 1000 ÷ (1000 + 1000) VOUT = 6 V
Equal resistor values divide the voltage equally.
Worked Example 2
Given:
- VIN = 12 V
- R1 = 2 kΩ
- R2 = 1 kΩ
VOUT = 12 × 1000 ÷ (2000 + 1000) VOUT = 4 V
Current Through the Divider
The current through both resistors is the same because they are connected in series.
I = VIN ÷ (R1 + R2)
The current should be significantly greater than the current drawn by the connected load to minimise errors.
Loaded Voltage Dividers
When a load is connected to the output, it effectively appears in parallel with the lower resistor.
This reduces the effective resistance and lowers the output voltage.
For accurate voltage dividers, the load resistance should normally be at least ten times greater than the lower resistor.
Choosing Resistor Values
- Use higher values to reduce power consumption.
- Use lower values when driving heavier loads.
- Avoid unnecessarily low resistances that waste power.
- Choose precision resistors for accurate output voltages.
- Consider resistor tolerance in precision applications.
Applications
- Microcontroller analogue inputs.
- Battery voltage monitoring.
- Reference voltage generation.
- Biasing transistor amplifiers.
- Operational amplifier circuits.
- Sensor interfaces.
- Audio attenuation.
- Signal conditioning.
- Power supply feedback networks.
- Voltage measurement circuits.
Real-World Examples
| Application | Purpose |
|---|---|
| Arduino | Reduce 12 V to a safe ADC voltage. |
| ESP32 | Battery voltage measurement. |
| UC3842 SMPS | Feedback voltage sensing. |
| Audio Amplifier | Input attenuation. |
| Comparator Circuit | Reference voltage generation. |
Advantages
- Simple and inexpensive.
- Requires only two resistors.
- Provides predictable output voltage.
- Easy to design and calculate.
- Suitable for low-current applications.
Limitations
- Output voltage changes if the load changes.
- Not suitable as a power supply.
- Wastes some power continuously.
- Output current is limited.
Common Mistakes
| Mistake | Result |
|---|---|
| Ignoring the load resistance. | Incorrect output voltage. |
| Using very high resistor values. | Noise and poor regulation. |
| Using very low resistor values. | Excessive power consumption. |
| Ignoring resistor tolerance. | Output voltage error. |
Key Points
- A voltage divider produces a fraction of the input voltage.
- It consists of resistors connected in series.
- The output voltage depends on the resistor ratio.
- Load resistance affects the output voltage.
- Voltage dividers are used extensively throughout analogue and digital electronics.