How to Size an LED Driver

Wattage is not the whole selection

Choosing a driver is not simply “buy the next wattage larger than the lights.” The driver has to match several conditions at once:

1. Output type (constant voltage or constant current)
2. Output voltage
3. Connected wattage / load
4. Input voltage
5. Dimming or control
6. Installation and environment

This article focuses on wattage and load sizing, with real arithmetic and EMCOD constant-voltage examples. Wattage alone does not guarantee compatibility.

First: match output type and voltage

Size the load only after the driver output matches the LED product.

• 12 V DC LED product → a 12 V DC constant-voltage driver.
• 24 V DC LED product → a 24 V DC constant-voltage driver.
• A module marked in milliamps → constant current, such as ECC-UD. Do not pick a constant-voltage driver solely by wattage. Source: EMCOD catalog record

Read Constant Voltage vs Constant Current LED Drivers before sizing by wattage alone.

Core formulas

These are Projekt Supply working formulas. Use the published watts on the tape or fixture, then the published wattage class on the driver specification sheet. Projekt Supply calculation

Example 1: LED tape

“Potentially suitable based on wattage” means only that the connected load does not exceed the driver’s published capacity. Output voltage, input voltage, minimum load, dimming, environmental rating and manufacturer instructions must also match.

Utilization

Driver utilization % = connected load ÷ driver rated wattage × 100. For the tape example on a 96 W class:

This page does not publish an EMCOD-specific maximum utilization rule. The current catalog stores wattage class, not a required operating percentage. Source: EMCOD manufacturer specifications

Manufacturer maximum versus design headroom

The specification sheet states the published capacity. Design headroom is a separate choice. Some designers leave extra capacity for future expansion, temperature, real-world load variation, or a project standard. That is a design decision, not automatically an EMCOD requirement, and this guide does not claim that LED drivers must always be loaded to 80%.

Example 2: fixtures

All other electrical characteristics must still match.

Example 3: 12 V vs 24 V current

The lighting still consumes approximately 120 watts. The higher-voltage system requires less current to deliver the same power. Projekt Supply explanation

The fixture or tape operating voltage determines which output voltage is valid. A 24 V driver may not power a 12 V product. Independent source: U.S. Department of Energy

Compare 12 V and 24 V current, voltage drop, and EMCOD examples in 12V vs 24V LED Drivers.

EMCOD 12 V constant-voltage examples

Rows come from current catalog wattage, input voltage, and MPNs that encode 12 V DC output. This is a useful subset, not the full driver catalog. Source: EMCOD catalog record

EMCOD 24 V constant-voltage examples

Narrowing an example requirement

Example requirement: 24 V DC, 70.4 W connected load, phase-dimmable, 120 V input.

1. Remove 12 V drivers.
2. Remove drivers below 70.4 W. In the 24 V table, 60 W rows drop out; 96 W and 150 W remain.
3. Keep rows whose listed input includes 120 V. Catalog examples include MLE96-24DC-P at 120 V 50/60 Hz, and universal-input 96 W rows such as MLE96-24DC-UD. Source: EMCOD manufacturer specifications
4. Phase dimming cannot be confirmed from wattage and the catalog 5-in-1 label. MLE-UD and ECV-UD are labeled universal 5-in-1; ES-UD is labeled PWM; MLE-P is not labeled as 5-in-1. This page does not pick one exact MPN for phase dimming. Read the specification sheet for the candidate you are buying. Source: EMCOD catalog record

Minimum load

Some LED drivers publish a minimum load or a minimum dimming-load condition. The EMCOD catalog fields used on this page store rated wattage, not a minimum-load percentage, so this article does not generalize a minimum-load rule across families. If the specification sheet for a specific MPN states a minimum, follow that sheet—especially on very small LED loads, dimming, and replacements. Source: EMCOD manufacturer specifications

Don’t forget input voltage

Driver output may be 12 V DC or 24 V DC while input may be 120 V AC or a universal 100–277 V range. A 24 V output designation does not tell you the input.

• MLE60-24DC-P is cataloged 24 V DC output and 120 V 50/60 Hz input. Source: EMCOD catalog record
• MLE60-24DC-UD is cataloged 24 V DC output and 100–277 V AC 50/60 Hz input. Source: EMCOD catalog record
• EDR60-24DC is cataloged 24 V DC output and 110–277 V 50/60 Hz input. Source: EMCOD catalog record

Dimming still has to match

A driver can have the correct voltage and wattage and still be the wrong driver if the control method is incompatible. Catalog labels on these families: MLE-UD and ECV-UD as universal 5-in-1; ES-UD as electronic PWM; EDR as a universal DIN-rail driver. This page does not invent forward-phase, reverse-phase, 0/1–10 V, PWM, or resistance lists beyond those catalog labels. Confirm methods on the MPN sheet. Source: EMCOD catalog record

Continue in LED Driver Dimming Explained.

Installation environment

Also verify dry, damp, or wet listing; NEMA enclosure where printed; junction-box versus DIN-rail; and Class 1 / Class 2 where the project requires it. Not every EMCOD driver is wet-location rated. Catalog examples: MLE-P is Dry / Damp; MLE-UD and ECV-UD list Dry, Damp, Wet; EDR is Dry / Damp and DIN-rail. Source: EMCOD catalog record

Replacement example

Existing nameplate: MLE60-24DC-UD. Catalog fields for that MPN include a 60 W class, 24 V DC output encoded in the MPN, 100–277 V AC input, Dry / Damp / Wet, and the UD series label. Source: EMCOD manufacturer specifications

Replacing it with another 60 W driver is not sufficient if output voltage or control type differs. Match family, wattage class, output, input, dimming suffix, and listing, then confirm the specification sheet.

Continue in EMCOD Replacement Guide.

Common LED driver sizing mistakes

1. Matching wattage but not voltage.
2. Ignoring AC versus DC output. Magnetic AC families and electronic DC families are not interchangeable by wattage class.
3. Choosing a driver smaller than connected load.
4. Assuming every 60 W driver is interchangeable.
5. Ignoring dimming compatibility.
6. Ignoring input voltage. A 24 V output label does not identify 120 V versus 100–277 V input.
7. Ignoring dry, damp, or wet listing and enclosure type.
8. Assuming one design-headroom percentage applies to every product.
9. Replacing a constant-current driver with a constant-voltage driver because the wattage looks close.
10. Failing to verify the exact specification sheet before ordering.

Before ordering

• LED load type (tape, fixture, or module)
• Constant voltage or constant current
• Required output voltage
• Connected wattage
• Required driver capacity at or above that load
• Input voltage
• Dimming or control method
• Minimum load, if the specification sheet publishes one
• Class 1 / Class 2 where relevant
• Dry / damp / wet location
• Physical enclosure or installation type
• Exact manufacturer specification for the MPN

Common questions