How to select a suitable qualified LED driver?

 

LED lighting penetrates into everyone's life and becomes more intelligent and exquisite. When designing high quality and outstanding lamps, the design engineer must carefully understand the LED driver because it is the heart of the lamp. In this article, LEADPOWER will describe the most commonly used LED driver concepts and provides a method for selecting a suitable qualified LED driver.

1.What are LED drivers

LED drivers, also known as LED power supplies, typically convert AC (AC) to stable DC (DC) output, since light-emitting diodes (LEDs) are a unique component that only accepts DC input.

2. To describe the size of the LED drives

• External LED driver with an internal LED

LED drivers can be built into the lamp (inside), placed on the surface of the lamp, or even on the outside of the lamp (outside). Most low-power indoor lights, especially bulbs, use indoor LED drivers to make cheaper and better-looking products, but external LED drivers are commonly used for downlights and panel lights. Lights with built-in LED drivers get worse heat inside the lamp as the power increases further, so external LED drivers are used more in high-power applications such as street lamps, floodlights, stadium lights, and plant growth lights. Another advantage of external LED drivers is that they are easy to replace and maintain.

• Switch power supply and linear voltage regulator

Linear LED drivers are common in AC LED, tag, and light strip applications. They are very simple, requiring only a resistance or voltage regulator MOSFET or IC to generate a constant current for the LED. As a result, the Power Supply is easy to adapt and allows for an ultra-wide selection of constant-voltage power Supplies, such as 12V, 24V LED drivers. The disadvantage of linear voltage regulator is high voltage
Obviously, the biggest advantage of switching power supplies is their high efficiency, which results in high light efficiency, a key parameter for most lighting applications. Compared to AC LEDs, switching power supplies have higher power factor, surge resistance and less flickering.

• isolated and non-isolated LED drivers

When we compare the two items, both are called switching power supplies. Isolation designs have adequate voltage insulation between input and output, usually 4vin + 2000V according to UL and CE, and 3750 Vac according to 3C standards. Insulation prevents high input voltage from penetrating the output, thereby improving safety and sacrificing efficiency (~ -5%) and cost (~ + 50%) by using high-insulation transformers instead of inductors as human transmission components. The non-isolated design is the opposite, mainly using a low power built-in design.

• Constant current vs. Constant voltage LED Driver

There is no doubt that LEDs should be driven by constant current sources due to their special V-I characteristics, but constant voltage LED drivers can be used when there is a linear regulator or resistor in series with the LED to provide current limits. LEADPOWER have also prepared another article for you if you want to learn how to dim your LED light bar. Due to their much higher efficiency, constant-current LED drivers are the mainstay of general lighting such as bulbs, linear lights, downlights, street lamps, etc., while constant-voltage 12V, 24V and even 48V LED drivers are used for signage and strip as the primary solution. By using a constant voltage solution, the user can easily configure the amount of light as long as the total power does not exceed the power rating, thus providing great flexibility for field installation. LEADPOWER have another article explaining the difference between constant-voltage and constant-current LED drivers.

 

• Class I vs. Class II LED Driver

Here I and II are written in Roman numerals, not 1 and 2, which have a completely different meaning in the next term. Class I and Class II are concepts derived from IEC(International Electrotechnical Commission) standards, which both define the internal structure and electrical insulation of the power supply to provide safe shock protection. IEC Class I input LED drivers have basic insulation and should have protective ground connections to eliminate electric shock. IEC Level II input models have additional safety precautions such as double insulation or reinforced insulation, so there is no need to protect ground (ground) connections. Generally, Class I LED drivers have ground wires at the input, while Class II does not, but have higher levels of insulation from the input to the housing or output. This is the common notation used in categories 1 and 2.

• Class 1 vs. Class 2 LED Driver

Class 1 and Class 2 are NEC(National Electrical Code) concepts in Arabic numerals, describing the output characteristics of the power supply for dry position less than 60Vdc/wet position less than 30Vdc, current less than 5A, and power less than 100W, as well as detailed requirements for circuit design characteristics. The UL Level 2 LED driver is regulated by the UL1310 and UL8750. There are many benefits to using a Level 2 LED driver, whose output is considered a safety terminal and no additional protection is required on the LED module or luminaries, thus saving on the cost of insulation and safety testing. However, these limitations limit the number of LEDs that can be operated by Class 2 LED drivers.

Class 2 Specification

UL Class 1 includes all LED drivers outside the Class 2 range and is regulated by UL1012 and UL8750. Although Class 2 LED drivers have the good advantage of simplifying the safety design of lamps, Class I LED drivers are still widely used because of higher efficiency and more uniform light output due to lower output current and more LEDs in series. In practical applications, Class 2 LED drivers are more used in lights that are easy for users to touch, such as growth lights, while Class 1 LED drivers are more used in highly mounted lights, such as stadium lights and lamp pole lights.