LED Driver Calculator

LED Driver Calculator
Size a Constant-Current LED Driver
Vin Input / Supply Voltage
V
Vf LED Forward Voltage (per LED)
V
If LED Current (per string)
Ns LEDs in Series
Np Parallel Strings (optional, default: 1)
η Driver Efficiency (default: 85%)
%
LED Driver Specification
Recommended Topology
—
Output Voltage
—
Output Current
—
Output Power
—
Input Power
—
From supply
Input Current
—
Driver Heat Loss
—
Efficiency
—
Total LEDs
—
Comparison: Driver vs Resistor

Buck (Step-Down) Driver

Vin > Vout — the driver steps the voltage down to match the LED string.

Vin (higher) Buck Driver CC Regulator ↓ LED String Vout (lower) Constant If

Boost (Step-Up) Driver

Vin < Vout — the driver steps the voltage up to drive the LED string.

Vin (lower) Boost Driver CC Regulator ↑ LED String Vout (higher) Constant If

Buck-Boost Driver

Vin ≈ Vout — the driver handles both step-up and step-down as input varies.

Vin (varies) Buck-Boost CC Regulator ↑↓ LED String Vout (matched) Constant If

LED Driver Calculator

A resistor wastes the voltage difference between the supply and the LEDs as heat — typically 30–60% of total power. A switching constant-current driver converts that voltage efficiently, losing only 5–15%. This calculator tells you the exact driver specifications you need: output voltage, output current, output power, input power, heat generated, and which topology (buck, boost, or buck-boost) to use.

Core Formulas

Vout = Vf × Ns — required driver output voltage
Iout = If × Np — required driver output current
Pout = Vout × Iout — driver output power (LED power)
Pin = Pout / η — input power drawn from supply
Iin = Pin / Vin — input current from supply
Pheat = Pin − Pout — heat generated by the driver

Ns = LEDs per series string. Np = number of parallel strings. η = driver efficiency (decimal, e.g. 0.85 for 85%).

Driver Topologies

Buck (Step-Down)

Use when Vin is more than ~10% above Vout. The driver steps voltage down to match the LED string. This is the most common case: 12 V or 24 V supply driving a few LEDs in series. Buck drivers are the simplest, cheapest, and most efficient topology — 90–95% efficiency is typical for quality ICs.

Boost (Step-Up)

Use when Vin is more than ~10% below Vout. The driver steps voltage up. Typical scenario: a 5 V USB supply or 3.7 V lithium battery driving a long series string of LEDs with a total forward voltage of 15–30 V. Boost drivers are slightly less efficient than buck (85–92% typical) due to higher switch stress.

Buck-Boost (Step-Up/Down)

Use when Vin is close to Vout, or when Vin varies across a range that crosses Vout. Example: a battery dropping from 12 V to 9 V during discharge while the LED string needs 9.9 V. The driver handles both directions automatically. Buck-boost drivers are the most versatile but typically 2–5% less efficient than a pure buck or boost at any given operating point.

The calculator picks the topology automatically:
Vin > Vout × 1.1 → Buck
Vin < Vout × 0.9 → Boost
Vout × 0.9 ≤ Vin ≤ Vout × 1.1 → Buck-Boost

Worked Example — 12 V LED Strip (Buck)

30 white LEDs (Vf = 3.3 V, If = 20 mA) in 10 parallel strings of 3 LEDs each. Vin = 12 V, η = 85%.

Vout = 3.3 × 3 = 9.9 V
Iout = 0.020 × 10 = 200 mA
Pout = 9.9 × 0.200 = 1.98 W
Pin = 1.98 / 0.85 = 2.33 W
Iin = 2.33 / 12 = 194 mA
Pheat = 2.33 − 1.98 = 0.35 W
Topology: Buck (12 V > 9.9 V × 1.1 = 10.89 V)

Resistor comparison: The same 30-LED circuit with resistors draws 2.40 W total (see the LED Power Calculator) — 0.42 W wasted in resistors. The driver wastes only 0.35 W and draws 0.07 W less from the supply. The savings are modest here because the resistor circuit was already reasonably efficient (82.5%). The real difference shows at higher power.

Worked Example — High-Power COB Module (Boost)

A 32 V / 1 A COB LED module powered from a 24 V supply. η = 90%.

Vout = 32 V
Iout = 1.0 A
Pout = 32 × 1.0 = 32.0 W
Pin = 32.0 / 0.90 = 35.6 W
Iin = 35.6 / 24 = 1.48 A
Pheat = 35.6 − 32.0 = 3.6 W
Topology: Boost (24 V < 32 V × 0.9 = 28.8 V)

A resistor cannot step voltage up — this application requires a driver. The boost driver delivers 32 W to the LEDs while wasting only 3.6 W as heat. Input current is 1.48 A from the 24 V supply, so wire and connector sizing should handle at least 2 A.

Worked Example — Battery-Powered Flashlight (Boost)

6 white LEDs in series (Vf = 3.2 V each, If = 350 mA) powered by a 2S lithium pack (8.4 V full → 6.0 V empty). η = 82%.

Vout = 3.2 × 6 = 19.2 V
Iout = 350 mA
Pout = 19.2 × 0.350 = 6.72 W
Pin = 6.72 / 0.82 = 8.20 W
Iin (full battery) = 8.20 / 8.4 = 0.98 A
Iin (empty battery) = 8.20 / 6.0 = 1.37 A
Pheat = 8.20 − 6.72 = 1.48 W
Topology: Boost (both 8.4 V and 6.0 V are below 19.2 V)

In this case, Vin is always below Vout, so a pure boost driver works. But if the design used a 6S pack (25.2 V → 18.0 V), Vin would cross Vout during discharge — that is when buck-boost is required. The calculator detects this automatically based on the voltage relationship.

Driver vs. Resistor — When to Switch

The calculator shows a direct comparison when the topology is buck (Vin > Vout). Here is the decision framework:

Resistor efficiency = Vout / Vin × 100%
Driver efficiency = η (from data sheet)
Power saved = Pin(resistor) − Pin(driver)

Use a resistor when total LED power is under ~0.5 W and resistor efficiency is above 70%. The LED Resistor Calculator will size it for you. A resistor costs pennies, adds no switching noise, and the waste heat is trivial.

Use a driver when total LED power exceeds ~1 W, or resistor efficiency drops below ~70%, or the application is battery-powered (every milliwatt counts), or you need constant brightness regardless of supply voltage variation.

Selecting a Driver IC or Module

Key Specs to Match

Output voltage range — must cover Vf × Ns with margin. Check both the minimum and maximum output voltage in the data sheet.

Output current rating — must handle If × Np continuously. Derate by 20% for thermal margin.

Input voltage range — must cover your supply voltage across all operating conditions (battery sag, adapter tolerance, etc.).

Efficiency at your operating point — data sheet efficiency curves vary with Vin, Vout, and Iout. Find the curve that matches your conditions, not the headline number.

Dimming support — PWM dimming (switching the driver on/off rapidly) or analog dimming (reducing the current setpoint). PWM maintains colour temperature; analog is simpler but shifts colour at low currents.

Popular Driver ICs

Buck: AL8861 (1.5 A, up to 40 V input), LM3414 (1 A, 94% efficiency), TPS54200 (up to 28 V, internal FET).

Boost: LT3757 (40 V output, 2.5 V minimum input), TPS61169 (compact, for backlighting), LM3410 (up to 24 V output).

Buck-Boost: LT3791 (60 V in/out, 4 A), TPS63020 (low-power, 96% peak), LM3668 (automotive grade).

Thermal Considerations

The driver’s heat output (Pheat = Pin − Pout) must be dissipated. For Pheat under 1 W, the PCB copper area and IC package are usually sufficient. Above 1 W, add thermal vias, heatsink pads, or an external heatsink. Above 5 W, forced airflow or a dedicated heatsink is typically required. The calculator shows Pheat directly so you can plan the thermal design before selecting the IC. For detailed power dissipation analysis, see the Electrical Power Calculator.

Frequently Asked Questions

How do I know if I need buck, boost, or buck-boost?
Compare Vin to Vout (= Vf × Ns). Vin higher → buck. Vin lower → boost. Vin close to Vout or variable across both → buck-boost. The calculator picks this automatically.
What efficiency should I enter?
85% is a safe default for estimates. For accurate results, check the driver IC data sheet for the efficiency at your specific Vin, Vout, and Iout. Cheap modules are typically 80–85%. Quality ICs hit 90–95% in buck mode.
Can I drive LEDs in parallel without separate strings?
Not recommended. LEDs in parallel without individual current control will share current unevenly due to forward voltage tolerances. The hottest LED draws the most current, gets hotter, draws even more — thermal runaway. Always use one driver output per series string, or a driver with built-in current balancing.
Why does input current increase as the battery discharges?
The output power (Pout) stays constant — the LEDs need the same voltage and current regardless of input voltage. As Vin drops, Iin must increase to maintain the same Pin = Pout / η. This is normal switching converter behaviour. Size your wiring and battery for the maximum current at the lowest expected input voltage.
Can I use a voltage regulator instead of an LED driver?
A voltage regulator controls output voltage; LEDs need controlled current. You could use a voltage regulator with a small sense resistor to set the current, but a purpose-built LED driver does this more accurately and often more efficiently. Dedicated drivers also include features like dimming, open-LED protection, and short-circuit protection.
How many LEDs can I drive from one driver?
Limited by the driver’s maximum output voltage (sets max series LEDs) and maximum output current (sets max parallel strings). Multiply to get max total power: if the driver handles 36 V at 1 A, that is 36 W — enough for about 10 high-power white LEDs (3.2 V × 700 mA each in a suitable series/parallel arrangement).

Related LED Calculators

More tools from the LED family:

Browse all Electronics Calculators →

Last updated: March 2026