LED Parallel Array Calculator
This LED Parallel Array Calculator estimates branch current, total supply current, resistor values, LED count, resistor power, LED power, supply power, and current margin for parallel LED designs.
The calculator assumes one current-limiting resistor per parallel branch, which is the recommended approach for resistor-limited LED arrays.
Engineering tool
LED Parallel Array Calculator
Calculate current, resistor values, LED count, power, and supply requirements for parallel LED arrays with one resistor per branch.
Known LED branch current.
Voltage feeding all parallel branches.
Forward voltage of one LED at branch current.
LEDs connected in series inside each branch.
Number of identical LED branches connected in parallel.
Total supply current
80 mA
Result console
- Total supply current
- 80mA
- Total LED count
- 4LEDs
- Total LED power
- 160mW
- Total supply power
- 400mW
- Current per branch
- 20mA
- LED power per branch
- 40mW
- Total power loss
- 240mW
- Circuit efficiency
- 40%
- Recommended minimum supply current
- 100mA
- Recommended supply power rating
- 500mW
Array Summary
4 parallel branches, 1 LED per branch, 4 LEDs total, 4 current-limiting resistors required, 20 mA per branch, 80 mA total supply current.
Use one current-limiting resistor per parallel branch. A shared resistor is not the recommended design.
A large share of supply voltage is lost in current-limiting resistors, reducing efficiency.
Formula reference
LED Parallel Array Formulas
Use volts, amperes, ohms, and watts in the equations. The calculator converts engineering units before applying the formulas.
Itotal = Ibranch × NparallelNLEDtotal = Nseries × NparallelPLEDbranch = Vf × Ibranch × NseriesPLEDtotal = PLEDbranch × NparallelPsupply = Vs × ItotalPloss = Psupply - PLEDtotalVLEDbranch = Vf × NseriesVr = Vs - VLEDbranchRexact = Vr / IbranchIactual = Vr / RselectedPresistorBranch = Iactual² × RselectedEfficiency = PLEDtotal / Psupply × 100%Variable definitions
- Vs
- Supply voltage
- Vf
- Forward voltage of one LED
- Ibranch
- Current through one parallel branch
- Nseries
- LEDs connected in series per branch
- Nparallel
- Number of parallel branches
- R
- One current-limiting resistor per branch
Variable Definitions
- Parallel branches
- Identical LED strings connected across the same supply.
- LEDs per branch
- LEDs connected in series inside each parallel branch.
- Current per branch
- The current through one LED string and one resistor.
- Total supply current
- The sum of all parallel branch currents.
- Resistors required
- One current-limiting resistor is used for each parallel branch.
- Supply margin
- A 25% engineering allowance above calculated current for supply sizing.
How to Use
1. Choose the design mode
Start from known branch current, calculate resistor per branch, or analyze an existing array.
2. Enter branch geometry
Set the number of LEDs per branch and the number of parallel branches.
3. Check supply and heat
Review total supply current, resistor power, total power, efficiency, and warnings.
Worked Examples
Total Current
Four parallel branches at 20 mA each require 80 mA total supply current.
- Total supply current
- 80 mA
- Total LED count
- 4
- LED power per branch
- 40 mW
- Total LED power
- 160 mW
- Total supply power
- 400 mW
- Power loss
- 240 mW
- Efficiency
- 40%
- Recommended supply current
- at least 100 mA
Resistor Per Branch
A 5 V supply, 2 V LED, and 20 mA target current leave 3 V across each branch resistor, requiring 150 Ω.
- Voltage across each resistor
- 3 V
- Exact resistance per branch
- 150 Ω
- Recommended standard resistance
- 150 Ω
- Actual current per branch
- 20 mA
- Total supply current
- 80 mA
- Resistor power per branch
- 60 mW
- Total resistor power
- 240 mW
- Total LED power
- 160 mW
- Total supply power
- 400 mW
- Efficiency
- 40%
- Resistors required
- 4
- LEDs required
- 4
Use one resistor per branch
Each parallel branch should have its own current-limiting resistor for better current sharing.
Forward voltage is not identical
Small LED forward-voltage differences can cause current hogging in bare parallel LEDs.
Parallel branches add current
Total power-supply current equals the sum of all branch currents.
Watch resistor tolerance
Resistor tolerance and LED forward-voltage tolerance both affect branch current balance.
Check supply margin
A supply with no current margin may run hot, sag under load, or fail startup requirements.
Use drivers for larger arrays
Constant-current drivers are preferred for larger arrays and high-power LEDs.
Common Mistakes
- Using one resistor for several parallel branches.
- Ignoring total power-supply current.
- Using resistor current as total array current.
- Forgetting resistor power dissipation.
- Assuming every LED has identical forward voltage.
- Selecting a power supply with no current margin.
- Connecting more series LEDs than the supply voltage supports.
Support reference
FAQ
How do you calculate total current in a parallel LED array?
Multiply the current in one branch by the number of parallel branches: Itotal = Ibranch × Nparallel.
Should parallel LED branches share one resistor?
No. Parallel LED branches should normally use one current-limiting resistor per branch to reduce current imbalance.
Why do parallel LEDs have current imbalance?
LED forward voltage is not identical between devices. The branch with lower forward voltage can draw more current.
How do you calculate resistor power per branch?
Calculate branch current, then use Presistor = Ibranch² × R for the resistor in each branch.
How much supply current margin should I use?
This calculator uses a 25% engineering allowance by default. Final margin depends on product requirements, startup behavior, and temperature.
When should I use a constant-current LED driver?
Use a regulated constant-current driver for larger arrays, high-power LEDs, tight brightness matching, or efficient lighting designs.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
Engineering Guide
Understanding LEDs
Learn LED fundamentals including forward voltage, forward current, wavelength, color, luminous intensity, LED types, packages, current limiting, and thermal design.
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Engineering Guide
How to Choose the Right LED
Choose LEDs by application, forward voltage, current, brightness, wavelength, CCT, viewing angle, package, power, thermal behavior, and datasheet limits.
15 min · Intermediate
Engineering Blog
10 Common LED Design Mistakes (and How to Avoid Them)
Avoid LED design mistakes involving current limiting, resistor value, forward-voltage variation, excessive current, resistor power, parallel branches, polarity, brightness, thermal design, and color selection.
14 min · Intermediate
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Engineering Disclaimer
This calculator provides first-order estimates for parallel LED arrays. Verify LED matching, resistor tolerance, thermal behavior, supply current, PCB current capacity, and driver limits before production use.