What Is a Voltage Divider?
A voltage divider is a simple circuit that uses two series resistors to split an input voltage down to a lower output. The output is Vout = Vin × R2 / (R1 + R2). It is used for sensor readings, generating reference voltages and level-shifting down. It is not suitable for loads that draw significant current (the output sags).
A voltage divider is one of the most fundamental circuits: it uses two series resistors to lower an input voltage proportionally. It's the simplest way to get a smaller voltage from a larger one.
How Does It Work?
When two resistors are connected in series, the input voltage is shared across them in proportion to their values. The output is taken across the second resistor (R2). This behavior rests directly on Ohm's law and the series connection.
The Voltage Divider Formula
Vout = Vin × R2 / (R1 + R2)
Worked Example
Let Vin = 12 V, R1 = 10 kΩ and R2 = 5 kΩ. The output voltage is: Vout = 12 × 5000 / (10000 + 5000) = 12 × (1/3) = 4 V. By changing the ratio of the resistors you can set any output you want.
| R1 | R2 | Vin | Vout |
|---|---|---|---|
| 10 kΩ | 10 kΩ | 12 V | 6 V (half) |
| 10 kΩ | 5 kΩ | 12 V | 4 V |
| 1 kΩ | 2 kΩ | 9 V | 6 V |
Where Is It Used?
It's used for sensor reading (e.g. position with a potentiometer), generating a reference voltage and bringing a signal level down to a measurable range.
Common Mistakes
- Forgetting the loading effect: if a load that draws current is connected to the output, Vout drops; a divider is directly suitable only for low-current (high-impedance) loads.
- Using it as a power supply: a voltage divider can't power a load like a motor/LED; that needs a regulator.
- Choosing very low resistances: small resistors waste current (and heat) for nothing; very large ones are prone to noise.
Frequently Asked Questions
What is the voltage divider formula?+
Where is it used?+
Why does it fail under load?+
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