Reverse Parallel Resistor Calculator

Reverse Parallel Resistor Formula:

\[ R1 = \frac{R_{total} \times R2}{R2 - R_{total}} \]

Unknown Resistor (R₁): Ω

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1. What is a Reverse Parallel Resistor Calculator?

Definition: This calculator determines the value of an unknown resistor (R₁) needed in parallel with a known resistor (R₂) to achieve a desired total resistance.

Purpose: It helps electronics engineers and hobbyists design circuits with specific parallel resistance values.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ R1 = \frac{R_{total} \times R2}{R2 - R_{total}} \]

Where:

\( R1 \) — Unknown resistor value (ohms)
\( R_{total} \) — Desired total parallel resistance (ohms)
\( R2 \) — Known resistor value (ohms)

Explanation: The formula is derived from the parallel resistance formula rearranged to solve for R₁.

3. Importance of Parallel Resistance Calculation

Details: Accurate parallel resistance calculations are essential for circuit design, current limiting, voltage division, and impedance matching.

4. Using the Calculator

Tips: Enter the desired total resistance and the known resistor value. Note that R₂ must be greater than R_total for a valid solution.

5. Frequently Asked Questions (FAQ)

Q1: Why must R2 be greater than R_total?
A: The total parallel resistance is always less than the smallest resistor in the parallel combination.

Q2: What if I get a negative result?
A: This means your inputs are invalid (R₂ ≤ R_total). Check your values and try again.

Q3: Can I use this for more than two resistors?
A: No, this calculator is for two resistors only. For more resistors, calculate step by step.

Q4: How precise should my resistor values be?
A: Use standard resistor values with appropriate tolerance (1%, 5%, etc.) closest to your calculation.

Q5: Does this account for resistor tolerance?
A: No, consider resistor tolerances in your final circuit design for accurate results.