Constant current and constant voltage driver is a common circuit drive method, usually used in LED lighting electronic displays and other fields. Constant current and constant voltage drivers achieve stable and precise control of LED system brightness by controlling a constant current or voltage, respectively. The following will detail the meaning of constant current and constant voltage drivers, their advantages, and the difference between constant current and constant voltage drivers.
What does LED stand for?
LED (Light emitting diode) is a semiconductor light source that combines a P (+: positive) type semiconductor and a N (-: negative) type semiconductor. When a forward voltage is connected at both ends of the LED, the P-type semiconductor and the N-type semiconductor combine to trigger the release of light particles and finally radiate visible light.
LED technology was first developed in the 1960s and is now used in a wide variety of lighting devices, including:
- Home and retail environments – such as light strips and downlights
- Camera flash
- Monitor and TV
- Car lights, such as headlights, taillights, and brake lights
- Traffic signals
- Aircraft lighting
- Commercial atmosphere lighting for hotels, restaurants, and other hospitality venues
- Outdoor and underwater lighting systems
What is an LED driver?
LED lamps need a reliable power supply to operate. LED drivers convert alternating current (AC) to direct current (DC) to provide a constant power supply for LED luminaires. The LED driver provides a constant and uninterrupted power supply to the LED by recognizing the temperature and conductivity changes of the LED. This prevents overheating, flickering, color changes, and performance degradation of the LED system.
The driver of the LED light also provides overheating protection, which will completely shut down the lighting if the temperature is too high. Most LED devices are low voltage. LED transformers perform the same function for larger lighting systems that require more power.
Alternative names for LED drivers include:
- LED power supply
- LED light driver
- LED driver circuit
What is an LED driver used for?
An LED driver acts like a transformer for a low-voltage light bulb. LED lights are primarily low-voltage devices – typically 4V, 12V, or 24V – and are suitable for DC power supplies. However, the power supply of most wall outlets is not directly compatible with LEDs because they usually need to operate at higher voltages (between 120 and 277V) and they provide alternating current. Since the average voltage of LEDs is too low for conventional transformers to be compatible, specialized LED drivers are needed to convert high-voltage AC to low-voltage DC.
The relationship between current and voltage
The current and voltage of the diode are interdependent. If the voltage increases, the current increases exponentially; Conversely, if the current increases, then the voltage will only increase gradually (not nearly as significantly). As shown in the picture below:
Read the power formula below to better understand the relationship between voltage, current, and power:
(more detailed illustration about: How to Calculate Power for LED Strip Lights? )
Constant current LED driver
What is a constant current LED driver?
Constant current (CC) LED drivers can provide a stable and accurate current to an LED or LED array regardless of input voltage fluctuations or temperature changes. Specifically, the constant current driver will adjust the input voltage so that the input voltage is kept at a constant level so that the output current is constant. This constancy of the constant current driver is crucial because LEDs are very sensitive to changes in current, and small changes can lead to significant differences in light intensity, color, and LED lamp life, or can lead to LED damage.
What are the advantages of constant current LED drivers?
- Provide stable current and extend the service life of LED.
- Ensure the consistency of brightness of each LED light.
- Prevent thermal runaway.
- Constant current drivers usually have over-temperature protection, short-circuit protection, and over-voltage protection.
- Dimming compatibility (DALI, 0-10V, Triac dimming).
- Adapt to different numbers of LED lamps.
- Easy to integrate and miniaturize.
What are the disadvantages of constant current LED drivers?
- Use complexity: Using CC drivers can be more complicated than using CV drivers.
- Higher cost: CC drivers require additional circuits to regulate current.
Constant voltage LED driver
What is a constant voltage LED driver?
The constant voltage(CV) driver is a power supply device that provides a stable voltage output for the LED lighting fixture. The output voltage of a constant voltage driver is fixed, but its current output has a maximum rating. If the actual current requirements of the circuit do not exceed the range of its current rating, then the constant voltage driver can operate normally. Constant voltage drivers are suitable for a single direct current (DC) output voltage, of which the most common constant voltage drivers (or power supplies) are 12VDC or 24VDC. Constant voltage drivers are more common in multi-color displays and LED strips with built-in resistors.
What are the advantages of constant voltage LED drivers?
- Simple installation process.
- Low application cost.
What are the disadvantages of constant voltage LED drivers?
- Current is prone to excess.
- Low efficiency.
- Additional components may be needed to protect the operation of the LED lighting system.
Comparison between constant current and constant voltage drivers
Based on what we now know about constant current and constant voltage drivers, it is safe to say that constant current will be a better choice for LED lights. Because constant current drivers can provide a consistent level of brightness, constant voltage drivers often cause flickering. This deficiency also greatly reduces the life of LED lighting that uses constant voltage drivers, and LED lighting systems that use constant voltage drivers are generally less efficient. On the other hand, constant current drivers can operate independently and efficiently because constant current drivers do not require any additional components. Although constant current drivers are generally more expensive than constant voltage drivers, the efficiency of constant current drivers more than makes up for the extra cost.
Here are some of the main differences between constant voltage and constant current drivers in LED lighting applications:
| Constant Voltage | Constant Current |
| Fluctuating current and stable voltage | Fluctuating voltage and constant current |
| Current changes exponentially in a way that’s hard to control in order to keep the voltage consistent (when power needs to change) | Voltage moderately fluctuates and is easy to control, which creates a more stable current when power needs to change |
| Needs a current limiter | Regulator built-in |
| Less costly | More costly |
| Small scale uses | Large scale uses |
| Short lifespan | Long lifespan |
| Complicated | Simple |
| Excessive current | The right amount of current |
| Does not prevent thermal runaway | Prevent thermal runaway |
| LED strips, bars, etc. | High power LEDs |
What is thermal runaway?
Thermal runaway is a dangerous event. All semiconductors, including LEDs, generate heat when they work. The more electricity a device uses, the more heat it needs to emit. If the heat removed by the equipment is excessive, the equipment will overheat. When this happens, the performance of the device battery will be greatly reduced, and even lead to serious safety accidents.
Constant current drivers can effectively reduce the risk of thermal runaway occurrence by producing a stable current when the temperature changes.
How to choose an LED driver?
You need to consider the following aspects when choosing the right LED driver：
- Voltage of the main power supply.
- Total power consumption of LED system.
- Specific voltage or constant current requirements of LEDs.
- IP level.
- Dimming demand.
- Specific protection functions.
- LED application type.
If you want to learn more about how to choose an LED power supply, please read the related blogs below:
- How to Choose LED Strip Light Power Supply?
- How to Choose LED Strip Light Controllers?
- How to Connect LED Strip to Power Supply?
- Top 6 Considerations Before Buying LED Strip Lights
Choose from a variety of LED power supplies or drivers: