Constant Voltage vs Constant Current LED Driver: Which Do You Need?

Two words decide whether an LED fixture works at all: constant voltage and constant current. Get them backwards and the LEDs either never light or burn out in days. Yet most buyers meet these terms only after a fixture has failed, so this is the short version we wish every spec sheet printed up front.

What "constant voltage" means

A constant-voltage (CV) driver holds the output voltage steady — typically 12V, 24V, 36V or 48V — and lets the fixture decide how much current to draw. LED strips, sign modules and most "12V/24V" products already carry their own current-limiting resistors, so they need a fixed voltage supply. This is the default for the vast majority of decorative, architectural and signage jobs.

What "constant current" means

A constant-current (CC) driver holds the current steady — usually 350mA, 500mA, 700mA, 1050mA or 1500mA — and varies the voltage to keep that current constant as the LED's forward voltage shifts with temperature. Bare high-power LEDs (downlights, floodlights, street lights, high-bay modules) have no on-board regulation, so they will pull runaway current from a fixed-voltage source and cook themselves. They need a CC driver.

If the label says 350 mA or 700 mA, it wants constant current. Tell us the fixture spec and we will match it.

The two side by side

Why mixing them destroys fixtures

1. CV driver on a CC LED — the LED draws whatever current it can, heats up, and dies. We see this most when someone reuses a 12V strip supply on a 350mA downlight.
2. CC driver on a CV strip — the driver forces current the strip's resistors cannot limit, so the strip overheats or the driver faults out. Either way, no light.

Always read the fixture label before energising anything. If there is any doubt, send us a photo of the label and we will tell you which type you need.

Can one driver do both?

Some programmable or "dual-mode" drivers can be set to CV or CC at a fixed output, but they cost more and are rarely needed. For a standard install, pick the right type once and you avoid a truck roll. Our indoor drivers and IP67 drivers are available in constant-current versions from 100W upward for high-power fixture work.

What we need from you

Send the fixture label (voltage in volts, or current in milliamps), the total wattage, the install location, and the quantity. We will confirm constant voltage or constant current and quote the exact model — and tell you when a cheaper off-the-shelf unit is genuinely enough.