Quick answer: A constant voltage LED driver holds a fixed output of 12V or 24V DC and lets the LED strip or module draw whatever current it needs. Choose 24V for runs longer than about 5 metres to limit voltage drop, size the driver at 20–30% above the strip’s total wattage, and select an IP-rated unit whenever the installation is damp, outdoor or in a washdown area. A constant voltage driver is the wrong choice only when the load is a high-power COB array that needs regulated current instead.
Introduction
Flexible LED strip is the most forgiving lighting product ever put on a specification sheet and the easiest to get wrong. The strip itself rarely fails. What fails is the power supply behind it — undersized, mounted in the wrong place, or of the wrong type entirely. In commercial fit-outs, signage programmes and architectural lighting projects, the driver is where reliability is decided.
This guide covers the constant voltage LED driver specifically: what it does, why the constant voltage architecture is the correct match for strip and module loads, how to size and select one, how to install it so the installation performs as specified, and which specifications to verify on paper before ordering. It is written for lighting designers, electrical contractors, signage manufacturers and facility buyers who are specifying across a project rather than replacing a single failed unit.
What Is a Constant Voltage LED Driver?
A constant voltage (CV) LED driver is a power supply that maintains a fixed DC output voltage — typically 12V or 24V — regardless of how much current the connected load draws, up to the driver’s rated output. The load decides its own current. That is the key architectural difference from a constant current (CC) driver, which holds a fixed current and lets the voltage settle wherever the load requires.
This works for LED strip because strip is itself a constant voltage product. It is built as repeating segments, each containing LEDs in series with current-limiting resistors. As long as the supply voltage is correct and stable, every segment self-regulates. LED modules with on-board driver electronics behave the same way. By contrast, high-power single-die and COB arrays have no internal current limiting and need a CC driver to avoid thermal runaway.
| Characteristic | Constant voltage (CV) driver | Constant current (CC) driver |
|---|---|---|
| Output held constant | Voltage (12V or 24V DC) | Current (e.g. 700mA, 1050mA) |
| Typical load | LED strip, LED modules with on-board electronics | High-power COB arrays, street and flood luminaires |
| Sizing basis | Total load wattage plus 20–30% headroom | Forward current and voltage window of the array |
| Cutting or extending strip | Accepted within the driver’s wattage and voltage-drop limits | Not applicable — the array is fixed |
Getting this distinction wrong in either direction is expensive. A CC driver on strip forces a fixed current that the strip’s internal resistors cannot accept, and an oversized CV driver on a COB array leaves the array unprotected against thermal runaway. Our separate article on constant current vs constant voltage LED drivers works through the selection logic for mixed projects.
Why It Matters
The driver determines three things that show up directly in project outcomes: whether light output is even across the installation, whether the system survives its first hot summer, and whether anyone is coming back to replace units under warranty.
- Consistent brightness end to end. Voltage drop along the strip’s copper traces means the far end of a long run sees less voltage and therefore emits less light. This is a driver selection and wiring problem, and the fix usually starts with choosing 24V over 12V.
- Service life in real ambient conditions. An LED driver’s electrolytic capacitors age faster at higher temperature. A driver loaded to 100% of its rating inside a warm ceiling void will not deliver the life its datasheet implies. Headroom is not conservatism; it is a service-life decision.
- Installation environment. Strips are frequently installed exactly where power supplies should not be — damp coves, exterior fascias, cold rooms, washdown areas. An IP rating is not a marketing feature here; it is what keeps the driver alive in the location the lighting actually needs.
- Flicker and compatibility. Some installations pair the strip with a dimmer or a control system. A CV driver with poor ripple performance or inadequate output capacitance produces visible flicker that no amount of re-terminating will fix.
How to Select the Right Unit
Three decisions cover most of the risk. Work through them in order.
Lock the Strip Voltage: 12V for Short Runs, 24V for Longer Runs
The voltage must match the strip, and the strip choice should follow the run length. Because voltage drop is proportional to current, doubling the supply voltage halves the current for the same wattage — and that roughly halves the drop along the same conductor. A 24V system therefore tolerates far longer runs before brightness becomes visibly uneven at the far end.
| Strip voltage | Practical single-feed run | Best for |
|---|---|---|
| 12V DC | Up to roughly 5 m before brightness visibly falls off | Short accents, cabinet and display lighting, single-colour signage |
| 24V DC | Roughly twice the usable length at the same power, so around 10 m | Cove and perimeter runs, long shopfront signage, commercial fit-outs |
Where a project needs to exceed these practical distances, the answer is not a larger driver but a different distribution approach: feed the strip from both ends, or inject power at intervals along the run from a bus. Both keep the strip voltage within tolerance instead of asking one driver to overcome the strip’s own resistance. Our comparison of 12V and 24V LED strip power supplies goes into the arithmetic in more detail.
Add 20–30% Wattage Headroom
Sum the wattage of every strip and module on the driver, then oversize. Two reasons, and both are practical rather than theoretical.
- Strip wattage ratings are nominal. Real consumption varies with bin, temperature and supply voltage, and a strip running slightly high on voltage will draw more than its label suggests.
- Drivers are derated in the enclosure. A unit rated for full output at 40°C does not deliver full output at 60°C in a ceiling void. The 20–30% margin absorbs both the derating and the temperature rise.
- Installations grow. Lighting schemes almost always gain a section during commissioning. Headroom means that conversation does not require a new power supply.
The margin also improves reliability in a way that is easy to demonstrate on paper. Running a driver at 70–80% of its rating instead of 100% reduces the internal temperature rise of its capacitors, which is the dominant factor in service life. Ultrathin constant voltage units such as the 100W 12V/24V slim LED driver and the 300W ultra-thin LED driver are designed exactly for this — low-profile housings that fit into coves and sign boxes, with the wattage headroom available to run below maximum.
Match the Environment with an IP-Rated Unit
Match the ingress protection rating to where the driver is mounted, not to where the strip is mounted. They are frequently in different conditions.
- Dry indoor ceiling or coves: a non-IP or IP20 enclosed driver is acceptable, but it still needs ventilation. Do not bury a driver under insulation.
- Damp interiors, cold rooms, kitchens: IP65 or IP67, with cable glands fitted properly. Condensation is the usual failure mechanism, not direct water contact.
- Exterior fascias and signage enclosures: IP67 minimum, and IP68 where the driver may sit in standing water or be regularly washed. Sealed enclosures also trap heat, so the derating check matters more, not less.
- Coated boards for humidity: conformal coating adds protection against condensation where a fully sealed enclosure is impractical. Ask whether it is applied by default or only on request.
Specifying LED Drivers for a Project?
Send us your strip wattage per run, the run lengths and the mounting environment. We will confirm the voltage class, wattage and IP rating per location — and quote a single consistent model line for the project.
How to Install & Integrate
Installation practice determines whether a correctly selected driver actually delivers the specification.
- Keep the driver close to the start of the run. Every metre of cable between driver and strip adds drop before the strip’s own traces are even considered. Where distance is unavoidable, use a heavier conductor for the feed.
- Size the feed cable for the load. At 12V and 20A, a run that would be trivial at mains voltage becomes a real conductor sizing decision. Undersized feed cable produces the same symptom as a weak driver.
- Inject power at both ends on long runs. Feeding a long strip from both ends roughly halves the effective drop and is a cheaper fix than moving up a voltage class mid-project.
- Observe polarity and use the marked cut points. Strips are polarity sensitive and only cuttable at marked intervals. A reversed section simply does not illuminate, which is easy to misdiagnose as a driver fault.
- Do not exceed the driver’s terminal capacity. Multiple strip runs on one driver should be brought back to a distribution point with appropriately rated connectors, not twisted together at the terminal block.
- Provide ventilation where the driver is enclosed. If the driver goes into a sealed sign box or a tight cove, allow the derating check to govern the wattage rather than the nameplate.
- Check the first fixture before installing the remainder. Measure voltage at the far end of the longest run under load. If it has fallen more than a few percent below nominal, correct the distribution before repeating the same mistake across the project.
Key Specifications to Check Before Purchasing
| Specification | Why it matters | What to verify |
|---|---|---|
| Output voltage and tolerance | A high output shortens strip life; a low one dims it | Nominal 12V or 24V with stated tolerance |
| Rated output wattage and current | The basis for the 20–30% headroom calculation | Continuous rating, not a peak figure |
| AC input range | Determines tolerance of supply variation on site | Wide-range input, typically 90–264V AC |
| Efficiency | Drives heat inside the enclosure, which drives life | Percentage at realistic load, not peak only |
| IP rating | Determines suitability for damp and outdoor locations | Rating with gland and cable entry included in the claim |
| Ripple and noise | Causes visible flicker, especially on camera or in dimmed systems | Millivolt figure with the measurement bandwidth stated |
| Protections | Overload on a long strip run should not destroy the driver | OVP, OCP, short-circuit and over-temperature |
| Thermal derating curve | Governs whether the nameplate applies in the enclosure | Full-power ambient temperature and derate slope |
| Compliance and warranty | Basis for project acceptance and lifecycle cost | CE, RoHS, and a warranty period stated in years |
LED Strip Driver Sizing Worksheet
Complete one row per driven run. It takes a few minutes and eliminates the two most common project errors: undersized drivers and 12V strip specified for a run that needed 24V.
| Step | What to record | Reference value | Your figure |
|---|---|---|---|
| 1 | Total strip wattage on this driver | Metres × watts per metre | ☐☐☐ W |
| 2 | Longest single run length | Compare against the 12V / 24V guidance | ☐☐☐☐ m |
| 3 | Strip voltage class selected | 12V short runs, 24V longer runs | ☐ 12V ☐ 24V |
| 4 | Required driver rating (step 1 × 1.25) | Rounds up to the next standard size | ☐☐☐ W |
| 5 | Output current at that wattage and voltage | Watts ÷ volts; check the driver’s max current | ☐☐☐ A |
| 6 | Worst-case ambient at the driver location | Ceiling voids and sealed boxes run hot | ☐☐☐ °C |
| 7 | IP rating required at that location | IP20 dry, IP65/67 damp, IP67/68 outdoor | ☐☐ IP |
FAQs
What is the difference between constant voltage and constant current LED drivers?
A constant voltage driver holds a fixed output of 12V or 24V DC and lets the load determine its own current, which suits LED strip and modules that contain their own current-limiting resistors. A constant current driver holds a fixed output current and lets the voltage settle, which suits high-power COB arrays and luminaires with no internal current limiting. Using the wrong type risks dim output, premature failure or unprotected thermal runaway in the load.
Should LED strips use a 12V or 24V driver?
Match the driver to the strip, and choose the strip by run length. 12V is fine for runs up to roughly 5 metres. Beyond that, voltage drop makes the far end visibly dimmer, so 24V is the better choice — for the same wattage it draws half the current, which roughly halves the drop along the same conductor and allows around twice the usable run length. For very long runs, feed from both ends or inject power at intervals rather than moving to a larger driver.
How much headroom is needed when sizing a constant voltage LED driver?
Allow 20–30% above the total strip wattage. The margin covers two things: real strip consumption is usually a little above the nominal rating, and the driver itself derates at higher ambient temperature, which is normal inside a ceiling void or sealed sign box. Running at 70–80% of the rated output instead of 100% also lowers internal component temperatures and extends service life.
Can a constant voltage LED driver be used outdoors?
Yes, provided the driver carries an appropriate IP rating — IP67 as a minimum for exterior use, and IP68 where standing water or regular washing is possible. Two additional checks matter. First, the cable glands and entry must maintain the rating, since most water ingress happens at the entry point. Second, a sealed enclosure traps heat, so confirm the derating curve still covers your load at the expected internal temperature before finalising the wattage.
Conclusion
A constant voltage LED driver is the correct power source for LED strip and modules because it matches how those products are built internally. Three decisions carry most of the outcome: use 24V whenever a run exceeds roughly five metres, size the driver 20–30% above total strip wattage so it runs cool, and select an IP rating that matches where the driver is actually mounted rather than where the light is. Add correct feed cable sizing, proper glands and a distribution point for multiple runs, and the driver stops being the weak point in the installation.
If you are assembling a driver schedule for a project, send our engineers your strip wattage, run lengths and mounting conditions. WEHO has manufactured constant voltage and constant current LED drivers from 10W to 400W since 2007, and we will confirm the correct model per location instead of leaving you to over-specify everything as a precaution.
Related Resources
- LED Driver product range — constant voltage and constant current families from 10W to 400W, in plastic and IP67 waterproof housings.
- 200W DC 12V/24V LED power supply — mid-range constant voltage driver for cove and signage runs.
- Best practices for LED strip power supplies in large installations — distribution, power injection and driver placement at project scale.
- Waterproof IP67 LED driver buying guide — what outdoor lighting actually requires from a driver.
- 24V LED drivers for strip and sign lighting — channel letters and illuminated signage applications.
