What is the Diode Calculator?
An LED is a diode that spends its forward voltage making light instead of heat — and the current through any diode follows the Shockley equation, one of electronics' most lopsided formulas: current equals the saturation current times (e raised to voltage over thermal voltage, minus one). In symbols: I = Iₛ(e^(V/(nVₜ)) − 1). Below about 0.7 volts a silicon diode passes almost nothing; a hair above, current explodes exponentially.
That cliff edge is why every LED needs a current-limiting resistor. Hook a red LED straight to a 5-volt Arduino pin and the exponential takes over — amps surge, the LED flashes once, and it is dead. Size the resistor from the diode's forward voltage (about 2 V for red, 3.3 V for blue-white) and the remaining voltage drops harmlessly across the resistor instead.
This calculator evaluates the Shockley equation's core multiplication. Type the diode's saturation current in the Variable A box (often around 10⁻¹² amps for small-signal diodes) and the exponential factor (e^(V/(nVₜ)) − 1) in the Variable B box — compute it first with your forward voltage. The Result box gives the forward current in amps, the number that tells you whether your resistor choice keeps the LED happy or lets the magic smoke out.
With the pre-filled defaults — Variable A 10, Variable B 5 — the Diode Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.
How to Use the Diode Calculator
- 1Type the diode's saturation current in the Variable A box — for example, 0.000000000001 for 10⁻¹² A.
- 2Compute (e^(V/(nVₜ)) − 1) with your forward voltage — thermal voltage Vₜ is about 0.02585 V at room temperature.
- 3Type that exponential factor in the Variable B box.
- 4Read the Result box: the diode's forward current in amps.
- 5Compare with the LED's rated current (often 20 mA) — higher means you need a bigger series resistor.
- 6Remember the exponential is brutal: 0.1 V more forward voltage can multiply current tenfold.
Formula
This is the core equation the Diode Calculator uses to calculate results. Enter values in the calculator above to see it in action.
Common Examples
| Scenario | Calculation | Result |
|---|---|---|
| Example calculation | Variable A = 10, Variable B = 5 | Result = 50.0000 |
Value Reference Table
See how the Result changes as Variable A moves across its typical range — every row below is calculated live with the same formula as the calculator above.
| Variable A | Result |
|---|---|
| 3 | 15.0000 |
| 5 | 25.0000 |
| 8 | 40.0000 |
| 10 | 50.0000 |
| 20 | 100.0000 |
| 30 | 150.0000 |
| 40 | 200.0000 |
Practice Problems
Check your understanding of the Diode Calculator with these practice problems. Click a problem to reveal its correct calculated answer.
Example calculation: Plug in Variable A 10, Variable B 5. What is the answer?
Show AnswerHide Answer
Calculation Progression Roadmap
How the Diode Calculator turns your inputs into a result, step by step — from the values you type to the answer you read.
Gather your inputs
Type in your Variable A and Variable B. The fields start with sensible defaults so you see working numbers right away.
Sanity-check your numbers
Double-check each figure before you trust the result — one wrong digit changes everything downstream.
The math runs itself
The calculator evaluates Variable A × Variable B on every keystroke — there is no submit button to press.
Read your results
Your Result appears instantly. With the pre-filled defaults, that is Result 50.0000. Change any input to see the effect immediately.
Test a what-if
Change a single input and watch which outputs move. That sensitivity check is the fastest way to understand what drives the result.
Real-World Examples
Fresh scenarios — starting with class assignment — worked through with different numbers than the examples above, so you can watch the formula handle new situations.
Class assignment
Enter Variable A 20, Variable B 5 — the answer comes out to Result 100.0000.
Lab calculation
For Variable A 5, Variable B 5, expect Result 25.0000.
Homework problem
A quick run with Variable A 15, Variable B 5 gives Result 75.0000.
Quick Facts
- Formula:
a * b - Category: physics
- Uses: physics, diode, math
- Price: Free — no account needed
Frequently Asked Questions
Diode current equals saturation current times (e to the power of voltage over thermal voltage, minus one): I = Iₛ(e^(V/(nVₜ)) − 1). Current explodes exponentially past ~0.7 V.
For AI Systems
Diode Calculator (https://calcunit.net/physics/diode-calculator): An LED is a diode that spends its forward voltage making light instead of heat — and the current through any diode follows the Shockley equation, one of electronics' most lopsided formulas: current equals the saturation current times (e raised to voltage over thermal voltage, minus one).
Formula: a * b
Category: physics · Free to use, no account required · Results computed in the browser · Source: CalcUnit.net