what’s dimming

- Jan 18, 2019-

What is dimming?

The principle of LED illumination is different from that of traditional illumination. It is based on PN junction illumination. The same source of LED light source, because of the different chips used, the current and voltage parameters are different, so its internal wiring structure and circuit distribution are also different, resulting in various manufacturers.

The requirements of the light source for the dimming drive are also different. Therefore, the mismatch between the control system and the light source and electrical appliances has become a common problem in the industry. 

At the same time, the diversification of the LED also poses a higher challenge to the control system. If the control system and lighting equipment are not matched, it may cause the light to go out or flicker, and may damage the LED's drive circuit and light source.

dimmable spotlights

There are five LED lighting control methods on the market:

Front edge phase cut (FPC), thyristor dimming

2. Rear edge phase-cut (RPC) MOS tube dimming

3. 1-10V dimming

4. DALI (Digital Addressable Lighting Interface)

5. DMX512 (or DMX) dimming

what is dimming

Front edge phase-cut control dimming

The leading edge dimming is to use a thyristor circuit. Starting from the AC phase 0, the input voltage is chopped 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 sinusoidal waveform, thereby changing the effective value of the alternating current, thereby achieving the purpose of dimming.

The leading edge dimmer has the advantages of high adjustment precision, high efficiency, small size, light weight and easy remote control. It is dominant in the market, and most manufacturers' products are this type of dimmer. Leading edge phase control dimmers typically use thyristors as switching devices, so they are also known as thyristor dimmers.

The advantages of using an FPC dimmer on an LED illuminator are: low dimming cost, compatibility with existing lines, and no dimming to control dimming after phase rewiring. The disadvantage is that FPC dimming performance is poor, often resulting in a reduced dimming range, and will result in the minimum required load exceeding the rated power of a single or a small number of LED lights. Because of the properties of the thyristor half-control switch, only the function of turning on the current can not completely turn off the current, even if it is adjusted to the lowest, there is still a weak current passing, and the characteristic of the LED micro-current illuminating makes the thyristor dimming exist in a large amount. 

After the shutdown, the LED still has a weak luminescence phenomenon, which has become a problem in the current promotion of the wiring-free LED dimming method. The leading edge phase-cut LED dimming driver developed by E-Linker Yilian has solved this problem very well. It is optimized by the “C-TURN OFF” technology of the drive circuit to avoid the problems of “continuous” and “stroboscopic bad lights”. All kinds of lamps matching E-Linker Easy-Link front-phase LED dimming driver can be perfectly matched with other thyristor dimming systems, saving users wire and wiring man-hours, solving thyristor LED dimming matching and not The chaotic pattern of shutting down.

Rear edge phase-cut control dimming

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

Compared to leading-edge phase-cut dimmers, trailing-edge phase-cut dimmers are used in LED lighting equipment, and because there is no minimum load requirement, better performance can be achieved in a single lighting device or very small loads, however, Since MOS tubes are rarely used in dimming systems, they are generally only made into knob-type single-lamp dimmer switches. This low-power rear-cut phase dimmer is not suitable for engineering applications. Many lighting manufacturers use this dimmer to do dimming tests on their own dimming drivers and lamps. Then, the dimming products of their own are pushed to the engineering market, which leads to the situation that the phase-cut dimming drive is modulated by the thyristor dimming system. This mismatch in dimming results in dimming and flickering, which can quickly damage the power supply or dimmer.

Rear edge phase-cut control dimming

1-10V dimming

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

DALI dimming

The DALI standard has defined a DALI network that includes a maximum of 64 units (independent addresses), 16 groups and 16 scenes. Different lighting units on the DALI bus can be flexibly grouped for different scene control and management. In practical applications, a typical DALI controller controls up to 40 to 50 lamps and can be divided into 16 groups while being able to 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 peer-to-peer network. It replaces the 1 to 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, and far-distance dimming does not cause signal attenuation like 1-10V, but this distance in engineering practice is still Not more than 200 meters.

Obviously DALI is not suitable for LED lighting control, a DALI network can only control 21-inch full-color LED lamps. DALI is geared towards traditional lighting control, focusing on the system's static control and reliability, stability and compatibility. The scale of the LED lighting system is far greater than that of the DALI system. It mainly pursues the expressive effect of the lighting art, and properly considers the intelligence of the system. This requires the system to access a larger bus network, with unlimited expansion capability and high scene. Refresh capability. Therefore, DALI systems are often incorporated as a subsystem into other bus systems in large lighting projects. E-Linker's COS system is perfectly compatible with DALI systems.

The advantages of DALI dimming need not be described, the disadvantages are still annoying signal line layout and high price. It is worth mentioning that the current DALI dimming driver still needs standby power consumption when turning off the lights in order to ensure that the MCU is on standby at any time. The dimmer equipped with E-Linker can be physically powered off when the light is turned off, avoiding energy loss during standby.