Deciding on an appropriate LED driver can be daunting given the wide range of options available. In this article, we will delve into the intricacies of LED drivers, focusing on the differences between Constant Current (CC) and Constant Voltage (CV) drivers, explaining when each is needed, along with their respective pros and cons.
What is an LED Driver?
Understanding that an LED driver regulates the current flowing through the LEDs is critical. All drivers are either constant voltage (CV), constant current (CC), or both. Your choice will depend on the type of LED fitting and intended application, among other factors.
What are the Characteristics of LEDs?
Currently, LEDs are the most significant source of lighting. As semiconductor diodes formed by combining two different materials to create a PN junction, they display unique electrical properties. When a direct current is applied, it causes the LED to emit light.
Similar to other semiconductors, LEDs allow current to pass in one direction while blocking the reverse current. They emit light when current flows from an anode (+) to cathode (-).
LED V-I Characteristic
LED characteristics reveal that minor changes in voltage can lead to significant variations in current flow. Typically, the forward voltage (Vf) ranges from 2-3.5 V with a forward current between 10-200mA. A slight change in voltage can result in substantial changes in forward current.
LED Temperature Coefficient
Many presume that fixing LED voltage ensures a constant current. However, the volt-ampere (V-I) characteristics of LEDs vary with temperature. If voltage remains fixed, current will change with temperature. This characteristic occurs due to the diode properties, which exhibit a negative temperature coefficient.
Usually, this coefficient is around -2mV per degree. As temperature rises, the V-I characteristic shifts left, altering performance.
The three curves in the accompanying image represent the behavior of LEDs at different temperatures, showing currents of 8mA, 20mA, and 37mA at the same 3.3V across varying temperatures.
What is a Constant Current LED Driver?
A constant current LED driver adjusts the voltage across the circuit to maintain a steady current flow. In essence, a constant current driver provides a fixed output current while allowing the voltage to vary. LEDs designed for constant current drivers require a specific current for optimal performance.
These drivers regulate current through the LED installation by fluctuating voltage. Elevated current leads to increased brightness, but without regulation, it risks LED burnout. This thermal runaway jeopardizes lifespan and quality, underlining the importance of constant current drivers.
Based on the temperature coefficient of LEDs, using a constant current driver can mitigate temperature rise issues.
When Do You Need a Constant Current LED Driver?
Constant current drivers are essential for LED fittings produced by the 'direct drive' approach, where the LED driver directly powers the LED circuit. This method is efficient and straightforward.
If you are constructing your fixture or extensively working with high-powered LEDs, constant current drivers are ideal. They can support either single bulbs or multiple LEDs in a series.
Detailed comparisons of CC and CV driver applications will further clarify their use cases.
- Use CC drivers for illumination, as they allow for consistent brightness control.
- These systems can be fine-tuned for optimal LED performance.
- Constant current drivers are suitable for backlighting, commercial displays, and signage.
What is a Constant Voltage LED Driver?
Constant voltage LED drivers serve as power supplies, commonly providing outputs of 12 VDC or 24 VDC. These drivers are designed to maintain a direct current output voltage. LEDs requiring constant voltage work best under specific voltage levels.
For devices with built-in current limiters, while voltage remains stable, current may vary since LEDs are typically wired in parallel. For instance, two lights will need double the current compared to one.
Can I Use a Constant Voltage LED Driver for Any LED Directly?
No, it’s inadvisable. As temperature increases, the V-I characteristic shifts. Fixing voltage while allowing current to rise leads to inefficiency and can dangerously elevate temperatures, potentially exceeding 80 or 90 degrees.
When employing a 3.3V constant voltage source at 20mA in room temperature, rising temperatures (up to 85 degrees) will increase current to 35-37mA, failing to enhance brightness. Higher currents can intensify heat, reducing lifespan.
In contrast, for high-power LED chips, a constant voltage source often results in severe light decay due to heat issues, making constant voltage supplies unacceptable for LEDs.
How to Fix This Problem?
Incorporating current limiting resistors into the circuit can mitigate risks. A CC driver ensures stable current flow, even with rising temperatures, preventing overdriving and thermal runaway—a vital factor for extending LED life.
When Do You Need a Constant Voltage LED Driver?
Constant voltage drivers efficiently run multiple LEDs wired in parallel, such as LED strips. For desired outcomes, LEDs are commonly arranged in parallel configurations. Lighting designers have created numerous LED products, including LED rope, bars, and strips, with built-in current limiters to maintain constant voltage.
In the LED strip circuit shown above, a current limiting resistor is evident, making it suitable for CV LED drivers. Cutting sections of LED strips won’t affect overall functionality as the voltage remains unchanged per section.
Using a CC LED driver for LED strips poses risks; if a 700mA driver operates six strips, cutting one increases the current flow to about 116mA for remaining strips, risking damage. Thus, constant voltage drivers are preferable for LED strips.
Constant Voltage LED Driver Applications
- Designed to power multiple parallel lights like LED strings and strips, ensuring satisfactory voltage supply across the entire assembly.
- Utilized in street lighting, moving advertisements, and various other applications such as hospitals and clinics.
Comparison of CC and CV Drivers
The differences in current and voltage characteristics between CC and CV drivers clarify their functionalities:
Constant Current Driver vs. Constant Voltage Driver
Current: Fixed vs. Variable
Voltage: Variable vs. Fixed
Constant Voltage Pros and Cons:
Pros:
- Impressive fault tolerance; failure of one light doesn’t affect others.
- Simple installation with flexibility for multiple fixtures.
- Cost-effective for extensive LED implementations.
- Conventional technology for designers and installers.
- Less variety in models, simplifying selection—12V and 24V being most common.
Cons:
- Overall lower efficiency compared to constant current systems.
- A current limiter must be integrated into the lights.
Constant Current Pros and Cons:
Pros:
- Prevents exceeding the maximum current limit, prolonging LED lifespan by avoiding burnout.
- Lower costs with exceptional efficiency.
- Simplifies output control for designers and engineers.
- Enables consistent brightness across lights.
- Well-suited for high-power applications.
Cons:
- Failure of one light impacts all due to series connections in constant current systems.
- Potential for uneven current and brightness in parallel setups.
What Type of LED Driver Do You Need?
Selecting an appropriate LED driver requires consideration of several factors:
- Application requirements.
- LED voltage and current ratings.
- Efficiency versus simplicity of installation.
- Ensure compliance with safety and energy efficiency standards.
For simple LED applications, constant voltage drivers are sufficient. However, as the number of LED strings increases, constant current drivers are preferred for managing current flow effectively.
Further reading on how to choose LED drivers is available if you're interested.
Summary
Although LEDs typically function with constant current, it is important to recognize that in certain situations, constant voltage supplies might be more suitable as discussed. We’ve provided a comparative overview of constant current and constant voltage drivers to assist in making the right choice.
Choosing the correct driver is crucial for your LED system, as it ensures the required power is supplied while maintaining safety and consistent performance.
uPowerTek’s CC and CV Drivers:
uPowerTek offers globally certified, high-quality LED drivers, both constant voltage and constant current. Recently, they introduced their new 800W Constant Voltage LED driver series, manufactured with a focus on consumer safety, national standards, and product quality management.
Why choose uPowerTek? As a member of the Digital Illumination Interface Alliance (DiiA), uPowerTek emphasizes quality and reliability, continuously delivering added value through innovative products such as NFC programmable drivers and high power growing light drivers.
For further details, explore our 5mm Ultra Thin Flexible Led Strip.
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