Calculator Inputs
Formula Used
For a loaded divider, the lower branch is not only R2. The load is connected in parallel with R2.
Equivalent lower branch: Rlower = R2 || Rload = 1 / (1/R2 + 1/Rload)
Loaded output voltage: Vout = Vin × [Rlower / (Rs + R1 + Rlower)]
Unloaded output voltage: Vout(unloaded) = Vin × [R2 / (Rs + R1 + R2)]
Total current: Itotal = Vin / (Rs + R1 + Rlower)
Load current: Iload = Vout / Rload
Loading error: [(Vunloaded − Vloaded) / Vunloaded] × 100
Thevenin resistance seen by the load: Rth = (R1 + Rs) || R2
How to Use This Calculator
- Enter the source voltage.
- Enter the upper resistor value R1.
- Enter the lower resistor value R2.
- Enter the load resistance connected across the output.
- Optionally add source resistance and tolerance values.
- Press Calculate to show the solved results above the form.
- Review voltage, current, power, loading error, and tolerance range.
- Use the CSV or PDF buttons to save the result table.
Example Data Table
| Vin (V) | R1 (Ω) | R2 (Ω) | Rload (Ω) | Rs (Ω) | Loaded Vout (V) | Loading Error (%) |
|---|---|---|---|---|---|---|
| 12 | 1000 | 2000 | 10000 | 50 | 7.361963 | 6.441718 |
| 9 | 470 | 1000 | 4700 | 10 | 5.902837 | 5.991957 |
| 24 | 2200 | 3300 | 15000 | 100 | 13.566557 | 8.392022 |
Voltage Divider with Load Guide
What This Circuit Does
A voltage divider reduces a higher source voltage to a lower output voltage. It uses two resistors in series. The output is taken across the lower resistor. This idea looks simple. Real circuits make it more practical. They also make it less ideal.
Why the Load Changes the Answer
When a load is attached to the output, it sits in parallel with the lower resistor. That lowers the effective resistance of the bottom branch. Because the lower branch gets smaller, the output voltage drops. The divider ratio also changes. This effect is called loading.
Why Engineers Must Check Loaded Output
Many learners first calculate the unloaded value. That value is useful, but it is not the final design value. Sensors, microcontroller pins, analog inputs, bias networks, and reference nodes all draw current. Even a small current can shift the output. That shift can break accuracy targets.
What This Calculator Solves
This calculator finds the loaded output voltage, unloaded output voltage, loading error, branch currents, power dissipation, and Thevenin values seen by the load. It also checks the lower branch equivalent resistance. That makes the tool useful for circuit analysis, electronics homework, design review, and lab work.
Why Tolerance Matters
Real resistors are not exact. A one percent or five percent part can move the output enough to matter. The tolerance section gives a practical minimum and maximum output estimate. That helps you judge if the divider is still safe for your ADC, transistor bias, or reference input.
Good Design Practice
Choose resistor values that balance current draw and stability. Very large resistor values reduce wasted current, but they make the node easier to disturb. Very small values improve stiffness, but they waste power. Source resistance also matters. If the source is not ideal, include it. That gives a better result.
Best Use Cases
Use this tool when checking a loaded sensor line, planning a bias point, scaling a battery voltage, or verifying a lab circuit. It gives fast, practical numbers. That saves time and reduces design mistakes.
FAQs
1. What is a voltage divider with load?
It is a resistor divider where an external device is connected across the output. That device behaves like a load resistance. The load changes the divider ratio and lowers the output voltage compared with the ideal open-circuit value.
2. Why is loaded output lower than unloaded output?
The load forms a parallel path with the lower resistor. That reduces the effective lower resistance. A smaller lower branch gets a smaller share of the input voltage, so the output drops.
3. When does loading become serious?
Loading becomes serious when the load resistance is not much larger than R2. A common design rule is to keep the load at least ten times larger than the lower resistor when you want a small error.
4. What does source resistance do?
Source resistance acts like an extra series resistor before the divider. It causes additional voltage drop and lowers the available output. Include it when the source is not ideal or when wiring resistance matters.
5. Can I use a divider to power a heavy load?
A divider is usually poor for powering heavy loads. The output changes with load current, and the resistors waste power. Use a regulator or converter when the load needs stable voltage and meaningful current.
6. What is Thevenin resistance here?
Thevenin resistance is the equivalent output resistance seen by the load. It shows how stiff the divider is. A smaller Thevenin resistance usually means the output changes less when the load changes.
7. Why does resistor tolerance matter?
Tolerance shifts the real resistor values away from nominal values. That changes the output voltage and currents. In sensitive analog circuits, even a small tolerance band can create noticeable output variation.
8. Is unloaded voltage ever enough?
Unloaded voltage is enough only when the output is truly open-circuit or the connected load is extremely large. For real design work, loaded output is the safer and more accurate number to use.