LED Drivers and How to Choose Them?
When choosing the various integrated circuit components for an electronic device, one will likely consider an LED as a lighting mechanism. After all, LED technology has garnered much popularity in the portable device market thanks to its increased efficiency and expanded lifespan. Of the various considerations one must keep in mind when implementing LED technology, the driver circuit is one of the most important. In this blog, we will discuss how LEDs work in portable devices and what nuances surround choosing a driver circuit for such applications.
A LED primarily consists of a diode device, which is a semiconductor material that is typically made from aluminum-gallium-arsenide (AlGaAs). In an LED circuit, two separate terminals are created by adding a P-type and N-type material to either side of the AlGaAs diode. To create an N-type material, engineers add atoms to the diode with extra electrons to create a negatively charged terminal. Conversely, P-type materials contain additional atoms that have more positively charged particles. When electricity is applied to this system, electrons move across the two terminals and experience a change in energy level. Specifically, if an electron has a drop in energy, it releases a high-energy visible photon.
In order for photon release to be consistent, the diode should have a constant power supply with the voltage matching the device's requirements. Drive circuits achieve this by transferring AC voltage to a continuous and compatible power supply. While drive circuits may vary in some features, they should share a few salient characteristics. Foremost, the variance in voltage output should stay within the +/- 10-15% range to prevent potentially damaging overvoltage incidents and ensure a minimum continuous current to produce light. Also, the drive circuit should demand low power input to increase the system's efficiency.
Other drive circuit characteristics to consider include Pulse Width Modification (PWM) and voltage boost. PWM is a method of dimming LED lights that involves turning energy to the diode on and off in a fast and repeatable pattern, thus creating the appearance of a less-bright light. While this dimming method is easy to implement and highly efficient, it is susceptible to electromagnetic interference (EMI), which can cause visible interruptions and produce audible noises. In addition, some LED applications, particularly those demanding a high brightness, require a higher voltage output than the standard input. As such, one must consider the voltage-boosting ability of the drive circuit. Like with PWM, the tradeoff for performance comes in the form of EMI, which increases linearly with the drive circuit's ability to boost voltage.
When choosing an LED drive circuit, one must first decide between a constant current (CC) or a constant voltage (CV) option. Typically, CC drivers are used in most small to medium-sized lighting configurations, such as those found in offices, residential buildings, stationary signs, and retail. Conversely, applications for CV drivers include stage lights, outdoor lighting, LED strips, and moving signs. One should also consider the LED's ampere requirements, which range from 4mA up to 700mA. Generally, it is safe to run LEDs at a lower current to increase their lifespan, but the opposite is not true. Using a current higher than the LED is rated for will quickly wear the system out and cause thermal hazards. Additionally, one should consider the life expectancy of various driver models. While the true lifespan will vary based on several factors, most drivers clearly state the mean time before failure (MBTF), allowing customers to make an informed decision.
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