Constant Current vs Constant Voltage LEDs

Choosing an LED driver sounds simple until constant current and constant voltage enter the scene. Both describe how a driver supplies power to an LED product. But they work differently and cannot be swapped freely.

A constant-voltage driver keeps voltage fixed. A constant-current driver keeps current fixed. The right choice depends on the LED product itself. So start with the product specification instead of guessing based on wattage.

This guide explains how both systems work, where they're used and how to choose the right driver.

Constant Current vs Constant Voltage at a Glance

Here's a quick version:

Constant voltage keeps voltage steady. Constant current keeps current steady. Always confirm the requirement on the product label, datasheet or installation guide.

What Is a Constant Voltage LED?

A constant-voltage LED is designed to run from a fixed DC voltage. Common examples include:

• 12V LED products
• 24V LED products
• LED strip lights
• LED modules

Some cabinet and architectural lighting

A typical setup looks like this:

230V AC mains → Constant-voltage driver → 12V or 24V LED product

The driver converts mains power into the lower DC voltage the LED needs. The output voltage must match the LED product.

For example:

• 12V LED → 12V constant-voltage driver
• 24V LED → 24V constant-voltage driver

Why Is Constant Voltage Common for LED Strip Lighting?

Many standard LED strips are built to run at either 12V or 24V DC. The strip contains LEDs and other parts designed around that supply voltage. That makes constant voltage practical for strips cut and installed in different lengths.

Bear in mind that strip length, power demand and installation layout can affect the choice.

See our guide to 12V vs 24V LED strip lights for a closer comparison. You can also browse our 12V and 24V LED strip lights.

How Is the Current Controlled?

In a constant-voltage system, the driver controls the voltage. The LED product then draws the current it needs by design.

That's the key difference. The driver holds voltage steady rather than directly regulating current through the LED.

What Is a Constant Current LED?

A constant-current system works the other way around. The driver keeps current at a set level and adjusts voltage within its operating range.

The current is usually shown in milliamps. Common examples include:

• 350mA
• 700mA

A constant-current driver may vary its output voltage while keeping the current fixed. The connected LED must suit both the current rating and the driver's voltage range.

Where Are Constant Current LEDs Used?

Constant-current systems are common in products such as:

• Individual high-power LEDs
• Some LED downlights
• Certain LED panels
• Specialist LED fittings
• Architectural lighting

Not every downlight or panel uses constant current. Some products use constant voltage or include their own driver.

Check the manufacturer's specification before replacing anything.

Why Do These LEDs Need Constant Current?

LEDs can be sensitive to excess current. Too much current can increase heat, reduce performance and shorten the LED's life.

A constant-current driver helps prevent this by regulating the current through the LED. In these systems, current control is part of the product's electrical design.

What's the Difference Between Constant Current and Constant Voltage?

The practical difference is what the driver regulates.

For constant-voltage systems, match the supply voltage first. Then calculate the total load and choose a driver with sufficient capacity.

For constant-current systems, match the required current first. Then confirm the LED sits within the driver's operating voltage range.

Why You Can't Simply Swap the Drivers

A driver's wattage only tells you how much power it can handle. It doesn't prove electrical compatibility.

A 24V LED strip needs a suitable 24V constant-voltage driver. A constant-current driver is not a substitute just because the wattage looks right.

The same applies in reverse. A 700mA fitting needs a compatible constant-current driver and a suitable voltage range.

How to Tell Whether Your LED Is Constant Current or Constant Voltage

You usually don't need test equipment. Start with the product information.

Check these in order:

• Product label
• Manufacturer datasheet
• Installation instructions
• Existing driver, if you are replacing one
• Dimming or control requirements

Check the Product Label

Look for markings such as:

• 12V DC
• 24V DC
• Constant voltage
• Constant current
• 350mA
• 700mA

A product marked 12V DC or 24V DC will usually use constant voltage. Another specified mainly in mA often uses constant current.

In any case, confirm the full specification before connecting anything.

Check the Manufacturer's Datasheet

The datasheet is usually the most reliable source. Look for:

• Input voltage
• Required driver output
• Current
• Wattage
• Driver type
• Operating voltage range
• Dimming requirements

If you're replacing a driver, compare the electrical ratings carefully. Matching the box size is not a recognised engineering method.

Don't Choose a Driver Based on Wattage Alone

This mistake is very common. A 50W driver isn't automatically suitable for a 40W LED load.

Use this order instead:

• Identify constant current or constant voltage.
• Match the required voltage or current.
• Check the voltage range where needed.
• Calculate the load.
• Check dimming and installation needs.

Driver type comes first. Wattage comes later.

How to Choose a Constant Voltage LED Driver

Once you confirm constant voltage, the process is straightforward.

Step 1: Match the Voltage

Match the LED voltage exactly. Once confirmed, choose from suitable constant-voltage LED drivers.

Step 2: Calculate the Total Wattage

For LED strip lighting, calculate the full load. Use:

Watts per metre × total strip length = total load

For example:

5m × 10W/m = 50W

That strip needs 50W of power. If one driver powers several strip sections, include them all.

See our guide on How to calculate LED strip power requirements for more details.

Step 3: Allow Suitable Headroom

Avoid running a driver at its absolute maximum all the time. Some spare capacity may be sensible, depending on the driver and installation.

Don't apply one percentage to every setup. Follow the driver's specification and the manufacturer's advice.

Bigger is not automatically better. You're choosing a driver, not entering a wattage contest.

Step 4: Check Dimming and Installation Conditions

Make sure the driver matches your control method and installation environment. You may need support for:

• Mains dimming
• PWM control
• DALI
• Smart controls
• Indoor use
• Damp areas
• Outdoor use

Check these before buying. Discovering them halfway through installation is less fun.

How to Choose a Constant Current LED Driver

Constant-current selection follows a similar process.

Step 1: Match the Required Current

Start with the LED's specified current. If it requires 700mA, choose a suitable 700mA constant-current driver.

Don't replace it with another current just because the wattage looks close.

Step 2: Check the Voltage Range

A constant-current driver may work across a voltage range. The LED must operate within that range.

Check both the minimum and maximum output voltage.

Step 3: Check the LED Configuration and Load

Make sure the driver suits the number and arrangement of connected LEDs. Follow the manufacturer's wiring requirements.

Don't use a simple watts-per-metre calculation for these systems. That method suits many LED strips, not every LED circuit on the planet.

Step 4: Check Dimming Requirements

If the fitting needs dimming, confirm the driver supports the required control method. The LED, driver and control system all need to agree.

What Happens If You Use the Wrong LED Driver?

An incompatible driver can cause several problems. These may include:

• LEDs not turning on
• Flickering
• Incorrect brightness
• Excess current
• Excess heat
• Driver overload
• Early failure
• Damage to the LED product

The exact result depends on the mismatch and the system's built-in protection. Some combinations simply fail to work. Others can cause longer-term damage.

What Happens If You Use Constant Voltage Instead of Constant Current?

A constant-current LED relies on the driver to regulate current. A standard constant-voltage supply doesn't regulate it in the same way.

That can lead to unstable operation, overheating or damage. Use the driver type specified for the LED.

What Happens If You Use Constant Current Instead of Constant Voltage?

A constant-current driver regulates a set current through the load. A constant-voltage LED product isn't designed to be powered that way.

The result may be poor performance, incorrect voltage or damage. Again, use the specified driver type.

Constant Current vs Constant Voltage for LED Strip Lights

Many standard LED strips use constant voltage, especially 12V and 24V products. A typical system looks like this:

Mains → Driver → Controller, if required → LED strip

The driver supplies the correct low-voltage DC power. A controller may then handle dimming, colour changes or smart control.

See our guide to LED strip wiring and power supplies for more detail.

Do RGB LED Strips Use Constant Voltage?

Many RGB LED strips use a constant-voltage supply. An LED controller manages the colour channels between the driver and strip.

The strip, controller, and driver must use compatible voltages. That trio needs to get along electrically, even if the app looks very friendly.

What About COB LED Strip Lighting?

COB describes how the LEDs are arranged on the strip. It doesn't tell you which driver type the strip needs.

Many COB strips use constant voltage, but always check the product specification. A useful way to remember it is:

• COB or SMD describes the LED technology
• Constant current or constant voltage describes how it's powered

Can Constant Current and Constant Voltage LEDs Be Connected Together?

Not on the same driver unless the system is designed for it.

Different LED products can have very different electrical needs. For example, a 24V strip cannot normally share a driver with a 700mA fitting.

Before connecting several products to one driver, check:

• Driver type
• Voltage or current
• Total load
• Wiring arrangement
• Manufacturer guidance

Some compatible constant-voltage products can share one correctly sized supply. Don't assume compatibility just because everything contains LEDs.

Constant Current vs Constant Voltage and Dimming

Dimming isn't decided by constant current or constant voltage alone. Both driver types can be dimmable.

Possible control methods include:

• Mains or phase-cut dimming
• PWM
• 0-10V control
• DALI
• Smart controls

Again, the LED, driver, and dimming method must all be compatible.

For LED strips, dimming often uses a controller on the low-voltage side. Other fittings may need a dedicated dimmable LED driver.

See our guides on wiring a dimmable LED driver and choosing LED controllers.

Constant Current or Constant Voltage: Which One Do You Need?

Start with the LED specification.

12V or 24V DC? Choose a matching constant-voltage driver.

350mA, 700mA or another fixed current? Choose a compatible constant-current driver.

Not sure? Check the manufacturer's datasheet before connecting anything. Then check wattage, operating range, dimming and installation needs.

In short, pick the driver type first, the electrical rating second, and the wattage third.

Once you know what your lighting setup requires, browse Simple Lighting's range of LED drivers.