Constant Voltage vs Constant Current LED Drivers: A Sign Maker’s Guide

What does constant voltage mean?

A CV power supply maintains its stated output voltage while the connected load draws the current it needs, up to the supply’s rating. Common outputs for sign lighting are 12V DC and 24V DC. The strip or module has its own current-limiting arrangement, which is why it can be connected to that fixed voltage.

For example, a 24V strip rated at 15W per metre draws approximately 75W over 5 metres, or 75 ÷ 24 = 3.125A. If two identical reels share one supply, the total nominal load is 150W and approximately 6.25A. Each branch still needs wiring and connectors rated for its current.

Do not assume every LED product is CV. “LED driver”, “transformer” and “power supply” are often used loosely in product listings; the output specification is what matters.

What does constant current mean?

A CC driver regulates output current, for example 350mA or 700mA. Its voltage adjusts within a stated working range as required by the connected LED array. This is common in light engines and some integrated luminaires where current must be controlled at the driver.

If a light engine requires 700mA and operates between 18V and 30V, select a 700mA driver whose constant-current voltage range covers the actual operating voltage. A nominal wattage alone cannot prove compatibility. Do not connect a bare current-driven LED array straight to an ordinary 24V supply unless its manufacturer explicitly specifies that arrangement.

CV and CC at a glance

The load specification tells you which column applies.

What about CV/CC and “constant power” drivers?

Some professional drivers operate in both a constant-voltage region and a constant-current region, or provide an adjustable output. That describes a particular model’s operating envelope; it does not mean you can swap it into any CV or CC installation. Consult the voltage–current graph, adjustment instructions and intended application in that model’s datasheet.

A strip dimmed with a low-voltage PWM controller still needs an appropriate CV power supply. The controller changes the delivered output to the strip; it does not change the fundamental voltage requirement.

Five checks before you order

Read both the LED load label and the proposed driver datasheet.

• Confirm CV or CC, then match the exact output voltage or regulated current.
• For CC, confirm the complete LED string stays inside the driver’s working voltage range.
• For CV, add every branch’s wattage and check the combined current at the rated voltage.
• Check dimming compatibility, IP protection, operating temperature and any derating.
• Follow the manufacturer’s connection diagram and maximum run length; use a competent person for mains-side work.

An example from sign making

A sign using 12V constant-voltage modules should be supplied from a suitably sized 12V CV output, even if a 24V supply has a higher wattage. Conversely, a 24V strip must not be connected to a 12V supply and expected to perform normally. Count the load and calculate capacity only after voltage and driver type are correct.

Glowfy supplies LED modules, strips and power supplies for professional signage. Check the live specification on each product page before selecting a model, or send our team the load label and the intended installation conditions.