Voltage Divider Calculator
Calculate the output voltage of a resistive voltage divider circuit.
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Result
How It Works
A voltage divider splits the input voltage proportionally based on the ratio of R2 to the total resistance (R1 + R2). Adding a load resistor (RL) in parallel with R2 reduces the output voltage.
Understanding Voltage Dividers
A voltage divider is one of the most fundamental circuits in electrical engineering. It uses two resistors in series to produce an output voltage that is a fraction of the input voltage. The output voltage depends on the ratio of the two resistances.
The Voltage Divider Formula
The basic voltage divider equation for an unloaded circuit is:
When a load resistance (RL) is connected in parallel with R2, the effective lower resistance becomes:
This reduces the output voltage. For accurate results, RL should be at least 10× larger than R2.
Engineering Applications
- Sensor interfacing: Reduce sensor output voltages (e.g., 0–5V) to match ADC input ranges (e.g., 0–3.3V) on microcontrollers.
- Bias circuits: Set the operating point (bias) of transistors and op-amps in amplifier circuits.
- Level shifting: Convert 5V logic signals to 3.3V levels for compatibility between different IC families.
- Reference voltages: Create stable reference voltages for comparators and measurement circuits.
- Battery monitoring: Scale battery voltages down to measurable ranges for battery management systems.
Important Design Considerations
Voltage dividers are simple but have limitations. They are not voltage regulators — the output changes with load current. For stable voltage under varying loads, use a voltage regulator IC instead. Also, the current flowing through the divider is wasted as heat, so choose resistance values high enough to minimize power consumption, but low enough to avoid noise pickup.
Frequently Asked Questions
Can I use a voltage divider as a power supply?
No. A voltage divider is not suitable as a power supply because its output voltage changes significantly with load current. For power applications, use a voltage regulator (such as a 7805 or LM317) or a buck/boost converter instead.
How do I choose resistor values for a voltage divider?
A common rule of thumb is to make the current through the divider at least 10 times the current drawn by the load. For example, if your load draws 1 mA, the divider should carry at least 10 mA. This keeps the output voltage stable. Typical divider resistances range from 1 kΩ to 100 kΩ.
What is the effect of load resistance on the output?
Adding a load in parallel with R2 reduces the effective lower resistance, which decreases the output voltage. The heavier the load (lower RL), the more the output drops. This calculator accounts for load resistance when you provide an RL value.
Why does my voltage divider output not match the calculation?
Common reasons include: resistor tolerance (5% or 1% resistors may be slightly off), load effects (any connected device draws current), and input impedance of measuring instruments. Always use 1% tolerance resistors for precision applications.
Reference Standards
IEC 60364 — Low-voltage electrical installations. NEC Article 210 — Branch Circuits. When designing voltage dividers for measurement circuits, follow IEC 61010 safety requirements.