Constant Current vs Constant Voltage LED Drivers: How to Choose
Constant current and constant voltage drivers are not interchangeable, and choosing the wrong one is the most common cause of both early LED failure and mysterious flicker. This guide gives you the decision rule, how to read each type of label, and what actually happens when the two are mismatched.
The one-line difference
A constant current (CC) driver holds the current fixed and lets the voltage vary within a window. A constant voltage (CV) driver holds the voltage fixed (typically 12 V, 24 V or 48 V) and lets the current vary with the load. LEDs are current-driven devices, so the question is simply: where does the current limiting live? If it is in the driver, you need CC. If it is already in the LED assembly, you need CV.
Constant current: how to read the label
A CC driver is specified as a current plus a voltage range, for example 1050 mA / 30–42 V DC. Three rules follow:
- The current must match the LED board's design current.
- The LED string voltage must sit inside the window — including the change in Vf between cold start and hot operation.
- LEDs in a CC string are wired in series, so the same current flows through every device and brightness stays uniform.
CC is the default for downlights, track lights, high bays, street lights and floodlights — anything built on LED boards or COB arrays.
Constant voltage: how the load takes over
A CV driver outputs a fixed 12 V, 24 V or 48 V. The current limiting sits in the LED product itself: resistors on a strip, a DC/DC stage on a module, or a driver-on-board. Because each unit regulates itself, CV loads are wired in parallel, and the driver's job is simply to supply enough current for the whole parallel set — size it at 80–90% of nameplate rather than 100%.
CV is the norm for LED strips, signage, facade and cove lighting, backlighting and any assembly sold by the metre.
Side-by-side
| Constant current (CC) | Constant voltage (CV) | |
|---|---|---|
| Regulates | Current (e.g. 700 mA, 1050 mA) | Voltage (12 V / 24 V / 48 V) |
| Output label | Current + voltage window | Fixed voltage + max power |
| Wiring | Series string | Parallel branches |
| Where current limiting lives | In the driver | In the LED assembly |
| Typical uses | Downlight, high bay, street light, floodlight | Strip, signage, facade, cove, modules |
| Failure mode if mismatched | Over-current through LEDs → shortened life | Over-current in wiring → heat, voltage drop |
What actually happens when you mismatch
Putting a CC driver on a CV product (a strip designed for 24 V fed by a 700 mA driver) makes the driver hunt: it will drive whatever voltage is needed to push 700 mA, which usually exceeds the strip's rating and destroys it. Putting a CV driver on a CC board is worse in slow motion — the LEDs draw current limited only by their own Vf, run hot, and drift in colour. Either way the failure looks like "the LEDs were bad".
Choosing by application
- Downlights, track, spotlights — CC, 350–700 mA.
- High bay, industrial — CC, 700–1400 mA, check surge and tc.
- Street and area lighting — CC, often with DALI 2.0 or Zhaga / D4i provision.
- Strip, cove, signage — CV 24 V (48 V for long runs to cut voltage drop).
- Facade and landscape — CV 24 V with IP67 drivers, or CC where fixtures are discrete luminaires.
When a single platform has to cover both, adjustable CC drivers with NFC or DIP-switch current setting let one part number serve several fixtures — worth asking about before you freeze the BOM.
Frequently Asked Questions
Can a constant voltage driver run a constant current LED?
Not safely. Without the driver limiting current, the LED draws whatever its forward voltage allows at that temperature, which leads to overheating and colour shift. Use a CC driver, or an LED assembly with built-in current regulation.
Why is 24 V more common than 12 V for strips?
Half the current for the same power, which means less voltage drop along the run and thinner cable. Long runs go further to 48 V for the same reason.
How much headroom should I leave on a CV driver?
Size the load at roughly 80–90% of the driver's rated power. Running a CV driver at its nameplate limit continuously raises internal temperature and shortens capacitor life.
Do CC and CV drivers dim differently?
The control signal (0-10 V, DALI, PWM) is the same, but the response differs: CC drivers regulate current down towards a minimum, while CV systems usually PWM the output or dim at the LED module. Check the dimming curve and flicker data at low levels, not just the interface name.