How to dim LED?

 The principle of LED light emission is different from traditional lighting . It relies on PN junction to emit light. LED light sources with the same power have different chips and different current and voltage parameters, so their internal wiring structures and circuit distributions are also different, which leads to different requirements for dimming drive of light sources from different manufacturers. Therefore, the mismatch between control system and light source electrical appliances has become a common problem in the industry. At the same time, the diversification of LEDs has also posed higher challenges to the control system. If the control system and lighting equipment are not matched, the lights may go out or flicker, and may damage the LED drive circuit and light source.

There are five ways to control LED lighting equipment 　　on the market :

　　1. Leading Edge Phase Cutting (FPC), thyristor dimming

　　2. Trailing Edge Phase Cut (RPC) MOS tube dimming

　　3. 1-10V dimming

　　4. DALI (Digital Addressable Lighting Interface)

　　5. DMX512 (or DMX) dimming

　　Leading edge phase control dimming

　　Leading edge dimming uses a thyristor circuit to chop the input voltage from AC phase 0 until the thyristor is turned on. The principle is to adjust the conduction angle of each half-wave of the AC to change the sine waveform, thereby changing the effective value of the AC current to achieve the purpose of dimming.

　　Leading edge dimmers have the advantages of high adjustment accuracy, high efficiency, small size, light weight, and easy remote control. They dominate the market and most manufacturers' products are this type of dimmers. Leading edge phase control dimmers generally use thyristors as switching devices, so they are also called thyristor dimmers.

　　The advantages of using FPC dimmers on LED lighting are: low dimming cost, compatible with existing lines, no need to rewire trailing edge phase-cut control dimming. The disadvantage is that FPC dimming performance is poor, which usually leads to a narrow dimming range and causes the minimum required load to exceed the rated power of a single or a small number of LED lighting lamps. Because the properties of the thyristor semi-controlled switch only have the function of turning on the current, but cannot completely shut off the current, even if it is adjusted to the lowest, there is still a weak current passing through, and the characteristics of LED micro-current light emission make it difficult to promote this wiring-free LED dimming method. The cutting-edge phase-cut LED dimming driver professionally developed by E-Linker solves this problem well, and optimizes the "C-TURN OFF" technology of the drive circuit to avoid problems such as "unable to turn off" and "stroboscopic broken lights". All kinds of lamps matched with E-Linker's leading-edge phase-cut LED dimming driver can perfectly match with other thyristor dimming systems, saving users wires and wiring hours, and solving the chaotic pattern of thyristor LED dimming matching and non-shutdown　　.

　　The trailing-edge phase-cut control dimmer is made of field effect transistor (FET) or insulated gate bipolar transistor (IGBT) devices. The trailing-edge phase-cut dimmer generally uses MOSFET as the switching device, so it is also called MOSFET dimmer, commonly known as "MOS tube". MOSFET is a fully controlled switch, which can be controlled to be on or off, so there is no phenomenon that the thyristor dimmer cannot be completely turned off. In addition, the MOSFET dimming circuit is more suitable for capacitive load dimming than the thyristor, but because of the high cost and the relatively complex dimming circuit, it is not easy to make it stable, so the MOS tube dimming method has not developed, and the thyristor dimmer still occupies the vast majority of the dimming system market.

　　Compared with the leading edge phase-cut dimmer, the trailing edge phase-cut dimmer is used in LED lighting equipment. Since there is no minimum load requirement, it can achieve better performance on a single lighting device or a very small load. However, since MOS tubes are rarely used in dimming systems and are generally only made into knob-type single-lamp dimming switches, this low-power trailing edge phase-cut dimmer is not suitable for the engineering field. Many lighting manufacturers use this dimmer to perform dimming tests on their own dimming drivers and lamps. Then they push their own dimming products to the engineering market, resulting in the frequent use of thyristor dimming systems to modulate the trailing edge phase-cut dimming drivers in engineering. This mismatch in dimming methods causes dimming flickering, which can quickly damage the power supply or dimmer in severe cases.

　　1-10V dimming

　　There are two independent circuits in the 1-10V dimming device, one is a normal voltage circuit, which is used to turn on or off the power to the lighting equipment, and the other is a low-voltage circuit, which provides a reference voltage to tell the lighting equipment the dimming level. The 0-10V dimming controller was previously commonly used to control the dimming of fluorescent lamps. Now, because a constant power supply is added to the LED driver module and there is a dedicated control circuit, the 0-10V dimmer can also support a large number of LED lighting lamps. However, the application disadvantages are also very obvious. The low-voltage control signal requires an additional set of lines, which greatly increases the construction requirements.

　　DALI dimming

　　The DALI standard has defined a DALI network, including a maximum of 64 units (independently addressable), 16 groups and 16 scenes. Different lighting units on the DALI bus can be flexibly grouped to achieve different scene control and management. In actual applications, a typical DALI controller controls up to 40 to 50 lights, which can be divided into 16 groups and can process some actions in parallel. In a DALI network, 30 to 40 control instructions can be processed per second. This means that the controller needs to manage 2 dimming instructions per second for each lighting group. DALI is not a true point-to-point network. It replaces the 1-10V voltage interface to control the ballast. Compared with the traditional 1-10V dimming, the advantage of DALI is that each node has a unique address code and has feedback. The longer-distance dimming will not have signal attenuation like 1-10V, but in engineering practice, this distance should not exceed 200 meters. Obviously, DALI is not suitable for LED lighting control. A DALI network can only control 21 full-color LED lamps. DALI is oriented towards traditional lighting control, focusing on the static control, reliability, stability and compatibility of the system. The scale of LED lighting system is much larger than that of DALI system. It mainly pursues the artistic expression of lighting fixtures and takes into account the intelligence of the system. This requires the system to be connected to a larger bus network with unlimited expansion capability and high scene refresh capability. Therefore, DALI system is often incorporated into other bus systems as a subsystem in large lighting projects. E-Linker's COS system is perfectly compatible with DALI system.

　　The advantages of DALI dimming are self-explanatory, but the disadvantages are still the annoying signal line layout and high price. It is worth mentioning that the current DALI dimming driver still needs to consume power when the light is turned off in order to ensure that the microcontroller is always on standby. The dimmer equipped with E-Linker can physically cut off the power when the light is turned off to avoid energy loss during standby.

　　0DMX512 dimming

　　The DMX512 protocol was first developed by USITT (United States Institute of Theatre Technology) as a standard digital interface from the console to the way to control dimmers. DMX512 surpasses the analog system, but it cannot completely replace the analog system. The simplicity, reliability (if it can be installed and used correctly) and flexibility of DMX512 make it a protocol of choice when funds allow.

　　In practical applications, the control method of DMX512 is generally to design the power supply and controller together. The DMX512 controller controls 8 to 24 lines and directly drives the RBG lines of LED lamps. However, in building lighting projects, due to the large attenuation of DC lines, a controller must be installed every 12 meters, and the control bus is in parallel. Therefore, the wiring of the controller is very large, and it is even impossible to construct in many occasions. The DMX512 receiver needs to set the address so that it can clearly receive dimming instructions, which is also very inconvenient in practical applications. Multiple controllers are interconnected to control complex lighting solutions, and the operating software design will also be more complicated. Therefore, DMX512 is more suitable for occasions where lamps are concentrated together, such as stage lighting.

　　In summary, the main disadvantage of DMX controllers is that they require special wiring layouts and types, and require certain programming in order to set basic colors and scenes, which is more costly for later maintenance.