The Case for a Constant Current
By Shane Timmons, Product Marketing Manager
Not only has LED technology all but completely displaced conventional incandescent light bulbs and fluorescent tube lighting, it is used far more extensively than any other forms of lighting technology that have come before it. This includes functional and decorative ambient lighting in rooms, backlight illumination in commercial and retail signage, and even agricultural applications.
Why LED lighting?
From its humble beginning as a ‘little red dot’, the LED has come a long way. Now available in high brightness and a full spectrum of colors, LEDs have many advantages over incandescent and fluorescent light sources, including lower energy consumption, longer lifetime, smaller size, and physical robustness.
The lower power consumption and longer life of LED lighting products are benefiting the industry with lower running and maintenance costs, along with simple installation and low capital costs resulting in the massive uptake of the technology.
LED lighting is also easier to control, bringing on the advent of Smart Lighting. For the indoors, the brightness, color tone, and hue of the lighting adapts to the time of day, mood, or occupancy level. For the outdoors, Facade Smart Lighting creates stark or warmly lit architectural splendor or even a colorful rainbow - boosting noticeability.
Why should engineers opt for a constant current source?
Consider the choice between constant voltage and constant current. An LED emits light proportional to the current flowing through it. While the use of resistors, in constant voltage configurations, provides a current limit to each LED, any small fluctuation in the supply voltage will cause a significant change in the current flowing. This results in uneven light output. The change in current also produces an undesirable increase in heat dissipation. The more heat that is generated, the less efficient the LED becomes, causing it to consume more current, resulting in a shorter lifespan that ultimately leads to premature failure.
For these reasons, constant-current LED drivers are preferred over constant-voltage drivers to ensure even brightness and maximum lifetime.
The typical configuration has each driver and several LEDs connected in series to form strings, which can be deployed in repeating patterns on strips and individually in modules. This configuration provides flexibility for lighting designers. The number of LEDs within each string is determined by the intended supply voltage (typically 12V or 24V), the combined forward voltage of the LEDs, and the voltage drop across the driver.
High-precision constant-current drivers
For applications where matched, and therefore uniform, lighting is critical, so ultra-precise constant-current drivers are entering the market. For example, the BCR430U from Diodes Incorporated
maintains a highly stable output current, adjustable between 5mA and 100mA, and held at ±5% across temperature variations and supply voltage fluctuations. It also features an ultra-low dropout voltage of 115mV, which creates more voltage headroom to drive extra LEDs compared to similar solutions. With a low operating current of just 285µA, this new linear LED driver provides greater system efficiency than others available on the market.
The BCR430U requires no external power transistors or capacitors, which reduces the overall BoM cost and increases system reliability. The robust design is tolerant to potential overvoltage conditions caused by faults in the LEDs, supply transients, and handling accidents. Other advanced features include support for PWM-based dimming, a wide operating voltage of 5V to 42V, and parallel operation.
Integrated thermal protection limits the output current in the event of high operating temperatures, avoiding operational failure, and maximizing the working lifetime of the LEDs.
Further information on the range of LED products from Diodes Incorporated is available here https://www.diodes.com/products/power-management/led-drivers/