Photodiode Current
Iph = S × E × A
Quick answer
This calculator solves Iph = S × E × A for Photocurrent. With Responsivity 0.5 A/W, Irradiance 1.1 W/m², Active Area 10 mm², the result is 5.5 µA. It solves in 4 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
A photodiode generates current proportional to the incident optical power. The responsivity S relates the photocurrent to the optical power at a specific wavelength, typically peaking at 0.4-0.6 A/W for silicon photodiodes in the 800-900 nm range. The total optical power on the detector is the irradiance (power per unit area) multiplied by the active area of the photodiode. This relationship is fundamental to fiber optic receivers, light meters, optical encoders, and any system that converts light to an electrical signal.
Variables
- Iph — Photocurrent generated by the photodiode (A)
- S — Spectral responsivity at the wavelength of interest (A/W)
- E — Irradiance (optical power density) at the detector surface (W/m²)
- A — Active (photosensitive) area of the detector (m²)
Practical Notes
Responsivity varies with wavelength: silicon photodiodes work from 200-1100 nm, InGaAs from 800-1700 nm. Dark current (leakage with no light) sets the minimum detectable signal. Transimpedance amplifiers convert the photocurrent to voltage for processing. For precision measurements, operate the photodiode in photovoltaic mode (zero bias) for lowest noise, or photoconductive mode (reverse bias) for fastest speed.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| Iph | Photocurrent | µA | pA, nA, µA, mA, A, kA |
| S | Responsivity | — | A/W |
| E | Irradiance | — | W/m² |
| A | Active Area | mm² | mm², cm², m² |
Step by step
- 1. What you know: Responsivity 0.5 A/W, Irradiance 1.1 W/m², Active Area 10 mm²
- 2. The relation: Iph = S × E × A
- 3. Substitute: S = 0.5 A/W, E = 1.1 W/m², A = 10 mm²
- 4. Result: Photocurrent = 5.5 µA
Worked examples
Minimum range
Given: Responsivity 0.025 A/W, Irradiance 0.055 W/m², Active Area 0.1 mm²
Result: Photocurrent = 137.5 pA
Low range
Given: Responsivity 0.25 A/W, Irradiance 0.55 W/m², Active Area 1 mm²
Result: Photocurrent = 137.5 nA
Typical
Given: Responsivity 0.5 A/W, Irradiance 1.1 W/m², Active Area 10 mm²
Result: Photocurrent = 5.5 µA
High range
Given: Responsivity 0.8 A/W, Irradiance 1.76 W/m², Active Area 1 cm²
Result: Photocurrent = 140.8 µA
Maximum range
Given: Responsivity 8 A/W, Irradiance 17.6 W/m², Active Area 10 cm²
Result: Photocurrent = 140.8 mA
Solving for each variable
Solve for Photocurrent
Responsivity 0.025 A/W, Irradiance 0.055 W/m², Active Area 0.1 mm² → 137.5 pA
Solve for Responsivity
Photocurrent 100 nA, Irradiance 0.055 W/m², Active Area 0.1 mm² → 18.18 A/W
Solve for Irradiance
Photocurrent 100 nA, Responsivity 0.025 A/W, Active Area 0.1 mm² → 40 W/m²
Solve for Active Area
Photocurrent 100 nA, Responsivity 0.025 A/W, Irradiance 0.055 W/m² → 0.7273 cm²
How Photocurrent changes with Responsivity
| Responsivity (input) | Photocurrent (result) |
|---|---|
| 0.05 A/W | 0.55 µA |
| 0.125 A/W | 1.375 µA |
| 0.25 A/W | 2.75 µA |
| 0.375 A/W | 4.125 µA |
| 0.5 A/W | 5.5 µA |
| 0.75 A/W | 8.25 µA |
| 1 A/W | 11 µA |
| 2 A/W | 22 µA |
| 3.5 A/W | 38.5 µA |
| 5 A/W | 55 µA |
The same result in other units
| Unit | Value |
|---|---|
| pA | 5500000 |
| nA | 5500 |
| µA | 5.5 |
| mA | 0.0055 |
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<p><a href="https://vbatpower.com/formulas/optical-sensor/">Photodiode Current</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Photodiode Current?
Use Iph = S × E × A. With Responsivity 0.5 A/W, Irradiance 1.1 W/m², Active Area 10 mm², Photocurrent works out to 5.5 µA.
What is the formula for Photodiode Current?
The formula is Iph = S × E × A. A photodiode generates current proportional to the incident optical power.
How do you find Responsivity when you know the other values?
Rearrange for Responsivity: with Photocurrent 100 nA, Irradiance 0.055 W/m², Active Area 0.1 mm², Responsivity is 18.18 A/W.
How do you find Irradiance when you know the other values?
Rearrange for Irradiance: with Photocurrent 100 nA, Responsivity 0.025 A/W, Active Area 0.1 mm², Irradiance is 40 W/m².
What units does Photodiode Current use?
Photocurrent is shown in pA, nA, µA, mA. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
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