LEDs Connected in Parallel

When LEDs are connected in parallel, each branch is connected across the same supply voltage.

                 R1
+V ───────────/\/\/\───►|─── GND
                 LED

                 R2
+V ───────────/\/\/\───►|─── GND
                 LED

                 R3
+V ───────────/\/\/\───►|─── GND
                 LED

Each LED branch should normally have its own current-limiting resistor. This helps prevent one LED from taking substantially more current than another due to differences in forward voltage.

Why Use a Separate Resistor for Each LED?

LEDs do not all have exactly the same forward voltage. Even LEDs of the same type can have different electrical characteristics.

If several LEDs are connected directly in parallel with only one shared resistor, the LED with the lower forward voltage can take more current. This can result in uneven brightness and potentially excessive current.

A safer arrangement for individual LEDs is:

             R1
+V ───────/\/\/\────►|──── GND
                      LED

             R2
+V ───────/\/\/\────►|──── GND
                      LED

Parallel LED Resistor Formula

For each LED branch:

R = (Vsupply - VLED) / ILED

Each resistor is calculated according to the forward voltage and desired current of its LED.

Parallel LED Calculator

Example — Four Red LEDs on 12 V

Suppose four red LEDs are connected in parallel. Each LED has an approximate forward voltage of 2 V and each LED should operate at 10 mA.

Supply = 12 V

LED voltage = 2 V

Current per LED = 10 mA

The resistor voltage is:

VR = 12 - 2

VR = 10 V

The resistor for each branch is:

R = 10 / 0.010

R = 1000 Ω

Therefore each LED branch requires approximately:

1 kΩ

Because there are four branches at 10 mA each, the total LED current is:

IT = 10 mA × 4

IT = 40 mA

Parallel LED Calculator — Individual Branches

The following calculator allows each LED to have a different forward voltage and desired current. This is useful when different LED types are used in the same circuit.

LED Current in Parallel

The total current supplied by the power source is the sum of the currents through all LED branches.

IT = I1 + I2 + I3 + ...

For example, four LED branches each consuming 10 mA require:

IT = 10 + 10 + 10 + 10

IT = 40 mA

The power supply therefore needs to be capable of supplying at least the required total current, with appropriate margin.

Resistor Power

The power dissipated by each branch resistor is:

P = VR × I

or:

P = I² × R

For the four-LED example:

VR = 10 V

I = 10 mA

P = 10 × 0.010

P = 0.10 W

Each resistor dissipates approximately 100 mW.

Parallel LED Power Calculator

Different LED Colors in Parallel

Different LED colors can have different forward voltages. For example, a red LED may have a forward voltage around 2 V while a blue or white LED may have a forward voltage around 3 V.

If they are connected in parallel, each branch should be designed independently.

12 V
 │
 ├── R1 ── Red LED ── GND
 │
 ├── R2 ── Green LED ── GND
 │
 └── R3 ── Blue LED ── GND

The resistor for each branch is determined from that branch's LED forward voltage and desired current.

Parallel LEDs From a 5 V Supply

A 5 V supply can be used for several individual LED branches. For example, a red LED with approximately 2 V forward voltage leaves approximately 3 V for its current-limiting resistor.

VR = 5 - 2

VR = 3 V

At 10 mA:

R = 3 / 0.010

R = 300 Ω

Each identical LED branch would therefore use approximately 300 Ω for 10 mA, subject to the actual LED forward voltage and desired current.

Parallel LEDs From a 12 V Supply

With a 12 V supply and a red LED with approximately 2 V forward voltage:

VR = 12 - 2

VR = 10 V

At 10 mA:

R = 10 / 0.010

R = 1 kΩ

At 20 mA:

R = 10 / 0.020

R = 500 Ω

The resistor power should be checked in both cases.

Choosing the Resistor Power Rating

The resistor should be rated for more power than the calculated dissipation, with an appropriate safety margin.

For example, if a branch resistor dissipates 0.2 W, a ¼ W resistor may be marginal depending on the operating environment. A higher-rated resistor may provide better thermal margin.

LED Forward Voltage

Forward voltage depends on LED type, current and temperature. Typical values are approximate.

For accurate designs, use the forward voltage from the LED datasheet at the intended operating current.

Parallel LED Strings

For a larger LED arrangement, several complete LED strings can be connected in parallel.

                    R1
+V ───────────────/\/\/\──►|──►|── GND
                            LED LED

                    R2
+V ───────────────/\/\/\──►|──►|── GND
                            LED LED

Each string should have its own current-limiting resistor. This is generally preferable to placing one resistor in series with the entire parallel network.

Why One Resistor for Several Parallel LEDs Can Be Problematic

Consider two LEDs connected directly in parallel. If one LED has a slightly lower forward voltage, it can conduct more current.

That increased current can change its operating point and further increase the imbalance between the LEDs.

Individual resistors make the branches much more independent.

Common Applications

• LED indicator panels
• Instrument displays
• Control-panel indicators
• LED lighting assemblies
• Automotive indicator circuits
• Microcontroller LED outputs
• Multiple status indicators
• Parallel LED strings

Common Mistakes

• Connecting several LEDs directly in parallel.
• Using only one resistor for multiple independent LEDs.
• Ignoring differences in LED forward voltage.
• Exceeding the current rating of an LED.
• Using a resistor with insufficient power rating.
• Ignoring the total current required from the power supply.
• Ignoring supply-voltage variation.
• Assuming all LEDs have identical electrical characteristics.

Key Points

• Parallel LED branches have the same supply voltage.
• Current divides between the branches.
• Total current is the sum of all branch currents.
• Each LED should normally have its own current-limiting resistor.
• Different LEDs may require different resistor values.
• Resistor power must be checked for every branch.
• For parallel LED strings, each string should normally have its own resistor.
• LED forward voltage varies with device type, current and temperature.