Five dimming methods for LED lighting

Brief Introduction on LED Lighting Dim

In fact, most of the current LED lighting problems are caused by the mismatch between the control system and the light source electrical appliances, which has become a common problem in the industry, and the diversification of LEDs also poses higher challenges to the control system. Because the light-emitting principle of LED is different from traditional lighting, it relies on PN junction to emit light. The LED light source of the same power uses different chips and different current and voltage parameters, so its internal wiring structure and circuit distribution are also different, resulting in different production Manufacturers’ light sources have different requirements for dimming drive. If the control system and lighting equipment are not matched, the lights may turn off or flicker, and may damage the LED drive circuit and light source.

There are five dimming methods for LED lighting equipment on the market:

1. Front edge phase cut (FPC), thyristor dimming
2. Rear-edge phase cut (RPC) Control dimming
3. 1-10VDC Dimming
4. DALI (Digital Addressable Lighting Interface)
5. DMX512 (or DMX)

  Front-edge Phase cut (FPC) Dimming

Front edge dimming is to use a thyristor circuit, starting from AC phase 0, the input voltage is chopped, and there is no voltage input until the thyristor is turned on. The principle is to adjust the conduction angle of each half wave of the alternating current to change the sine waveform, thereby changing the effective value of the alternating current, so as to achieve the purpose of dimming. Cutting-edge dimmers have the advantages of high adjustment accuracy, high efficiency, small size, light weight, and easy long-distance manipulation. They dominate the market, and most manufacturers’ products are this type of dimmer.

Front edge phase control dimmers generally use thyristors as switching devices, so it is also called thyristor dimmers. The advantages of using FPC dimmers on LED lighting are: low dimming cost, compatibility with existing circuits, No need to rewire. The disadvantage is that the FPC’s dimming performance is poor, which usually causes the dimming range to be reduced, and will cause the minimum required load to exceed the rated power of a single or a small amount of LED lighting.

Because of the properties of the SCR semi-controlled switch, only the function of turning on the current, but not completely turning off the current, even if it is adjusted to the lowest level, there is still a weak current flowing, and the light-emitting characteristics of the LED’s micro-current makes the use of thyristor dimming a large number of The phenomenon of weak light emission still exists after the LED is turned off, which has become a problem in the promotion of the current wiring-free LED dimming method.    The cutting-edge phase-cut LED dimming driver developed by E-Linker professionally solves this problem. The “C-TURNOFF” technology of the drive circuit is optimized to avoid problems such as “continuous off” and “flickering and broken lights”.

All kinds of lamps that match E-Linker’s front-cut LED dimming drive can be perfectly matched with other SCR dimming systems, saving users wire and wiring man-hours, and solving the matching and impossibility of SCR LED dimming. The chaotic pattern of shutdown.

Rear-edge phase cut (RPC) Control dimming

The trailing edge phase-cutting 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 SCR dimmer cannot be completely turned off.

In addition, MOSFET dimming circuits are more suitable for capacitive load dimming than SCRs. However, due to the high cost and relatively complex dimming circuits, and it is not easy to stabilize, the MOS dimming method has not been developed. Optical devices still occupy most of the dimming system market. Compared with the leading-edge phase-cut dimmer, the trailing-edge phase-cut dimmer is applied to LED lighting equipment. Since there is no minimum load requirement, it can achieve better performance on a single lighting equipment or a very small load. However, Since MOS tubes are rarely used in dimming systems, they are generally only made as knob-type single-lamp dimming switches. This low-power back-cut phase dimmer is not suitable for engineering.

Many lighting manufacturers use this dimmer to test their own dimming drivers and lamps. Then push its own dimming products to the engineering market, leading to the situation of phase-cut dimming drive after modulating with thyristor dimming system.

The mismatch of this dimming method causes dimming flicker, which can quickly damage the power supply or dimmer.

1-10VDC Dimming

There are two independent circuits in the 1-10V dimming device, one is an ordinary voltage circuit, which is used to turn on or off the power supply to the lighting equipment, and the other is a low-voltage circuit, which provides a reference voltage to tell the lighting equipment dimming level , 0-10V dimming controllers were commonly used in the dimming control of fluorescent lamps before. Now, because the constant power supply is added to the LED drive module and there are special control circuits, 0-10V dimmers can also support A lot of LED lighting.

But the application shortcomings are also very obvious. The low-voltage control signal requires an additional set of lines, which greatly increases the requirements for construction.

DALI (Digital Addressable Lighting Interface)

The DALI standard has defined a DALI network, including the largest 64 units (with independent addresses), 16 groups and 16 scenes. Different lighting units on the DALI bus can be flexibly grouped to achieve different scene control and management.

In practical applications, a typical DALI controller controls up to 40-50 lights, which can be divided into 16 groups, and can process some actions in parallel. In a DALI network, 30-40 control commands can be processed per second. This means that the controller needs to manage 2 dimming commands per second for each lighting group.

DALI is not a real point-to-point network, it is to replace 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 feedback. The dimming at a longer distance will not cause signal attenuation like 1-10V, but this distance is still 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 to traditional lighting control, focusing on the static control and reliability, stability and compatibility of the system.

The scale of the LED lighting system is much larger than that of the DALI system. It mainly pursues the artistic expression of lamps and lanterns, and appropriately takes into account the intelligentization of the system. This requires the system to be connected to a larger bus network, with unlimited expansion capabilities and higher scenarios. Refresh ability.

Therefore, DALI systems are often incorporated into other bus systems as a subsystem in large-scale lighting projects. E-Linker’s COS system is perfectly compatible with DALI system. The advantages of DALI dimming need not be repeated, but the disadvantages are still annoying signal line layout and high price.

It is worth mentioning that the current DALI dimming driver, in order to ensure that the MCU is always on standby, still needs standby power consumption when the lights are turned off. The dimmer equipped with E-Linker can physically cut off the power when the lights are turned off to avoid energy loss during standby.

DMX512 (or DMX)

The DMX512 protocol was first developed by the USITT (American Theater Technology Association) to control the dimmer from the standard digital interface used in the console.

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 permit.

In practical applications, the control method of DMX512 is generally to design the power supply and the controller together.

The DMX512 controller controls 8-24 lines and directly drives the RBG line of the LED lamps. However, in the building lighting project, due to the weak DC line, it is required to install a controller at about 12 meters, and the control bus is parallel. Therefore, the controller has a lot of wiring, and in many cases it can’t even be constructed.

DMX512 receiver needs to set the address so that it can clearly receive dimming commands, which is also very inconvenient in practical applications. Multiple controllers are interconnected to control complex lighting schemes, and the design of operating software will be more complicated.

From this analysis, we can see that DMX512 is more suitable for occasions where lamps and lanterns are concentrated, such as stage lighting. In summary, the main disadvantage of the DMX controller is that it requires a special wiring layout and type, and a certain programming is required to set the basic colors and scenes, which is more costly for later maintenance.