The Six Dimming Methods for LED Lighting
Due to the improvement of people's living standards, lamps have gradually extended from simple switches to dimming. With the development of the Internet of Things, everything is controlled by multiple connections. LED lighting is easy to control, which is very in line with the needs of the Internet of Things. Now there are many dimming and control methods on the market. Today, we will briefly introduce the dimming methods of commonly used LED lamps.
There are six LED lighting control methods on the market:
1. Leading edge cutting (FPC), thyristor dimming
2. Trailing edge phase cut, (RPC) MOS tube dimming
3. 0/1-10VDC, analog circuit dimming
4. PWM dimming
5. DALI (Digital Addressable Lighting Interface)
6. DMX512 (or DMX)
1. Leading edge cutting (FPC)
Leading 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. Front-end dimmers have the advantages of high adjustment accuracy, high efficiency, small size, light weight, and easy long-distance operation. They are dominant in the market, and most manufacturers' products are this type of dimmers.
Leading-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 SCR 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 lamps of RISE Lighting adopt cutting-edge phase-cut LED dimming driver of BOKE, LIFUD and Eaglerise to solve this problem. The "C-TURNOFF" technology of the drive circuit is optimized to avoid "continuous off" and "strobe damage". "Lights" and other problems. All types of lamps driven by the front-cut LED dimming can be perfectly matched with other thyristor dimming systems, saving users wire and wiring man-hours, and solving the chaotic pattern of thyristor LED dimming matching and non-shutdown.
2. Trailing edge phase cut
The trailing edge phase cut control dimmer is made of field effect transistor (FET) or insulated gate bipolar transistor (IGBT) equipment. 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 the relatively complex dimming circuits, which are not easy to stabilize, the MOS dimming method has not been developed. SCR dimming 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, which leads to the situation of phase-cut dimming drive after modulating with thyristor dimming system.
The mismatch of this dimming mode leads to dimming flicker, which can quickly damage the power supply or dimmer.
3. 0/1-10VDC dimmable
There are two independent circuits in the 0/1-10V dimming device, one is an ordinary voltage circuit, used to switch 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 to adjust Light level, the 0-10V dimming controller was used to control the dimming of fluorescent lamps before. Now, because the constant power supply is added to the LED drive module and there is a special control circuit, the 0-10V dimmer is the same Can support a large number 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.
4. PWM dimming
This control mode is generally based on a DC constant voltage power supply, plus a constant current DC/DC converter that can achieve fast current control (or a PWM chopper switch is added to the output of the constant current power supply). Usually a chopping frequency of hundreds of Hz to 1KHz controls the working time of a constant current DC/DC converter (or PWM chopping switch) in a unit cycle, so as to obtain square wave output currents with different duty cycles and adjust the square wave output The duty cycle of the current is to adjust the average value of the output current, thereby changing the brightness of the LED lamp. Using PWM mode dimming, when the chopping frequency is above several hundred Hz, the human eye will not feel flicker or jitter.
One advantage of LED PWM dimming is that the light color of the light source does not change with the current. This control method adds a DC/DC converter to the original constant voltage source (or adds a PWM chopper switch to the original constant current source), increases the cost of the circuit, and increases the cost of the main circuit. loss. Under the same average current, the luminous efficiency of the LED light source under the PWM square wave current is lower than the luminous efficiency under the direct current, so compared with analog dimming, the energy saving effect of PWM dimming is worse.
5. DALI dimming
DALI dimming is a typical digitally controlled dimming method. The World DALI Association was established in 2001. The introduction and application of DALI technology has become the mainstream standard for digital dimming in Europe. DALI is a dedicated lighting control protocol, DALI system is suitable for scene control, light source failure status feedback. The DALI system gives new connotations to the lamps. Each lamp has an independent address. The DALI system does not require light sources and lamps, but requires ballasts, drivers and other components to comply with DALI standards, and the addresses of lamps are reflected by them.
The composition of DALI dimming system
DALI system composition:
DALI control equipment: send lighting control commands to the lighting network.
DALI control device: Receive and execute DALI standard commands issued by lighting control equipment.
DALI gateway: It is mainly responsible for the information exchange between the DALI bus system and other external protocol systems.
DALI auxiliary equipment:
DALI bus power supply: provide 16VDC power supply for DALI bus.
DALI bus repeater: provide relay drive for DALI bus, extend the communication distance of DALI bus.
DALI can form a network with a maximum of 64 short addresses and 16 group addresses, and one master can control one or more slaves.
Advantages/disadvantages of DALI dimming
DALI can dimming each lamp equipped with DALI driver. Different lighting units on the DALI bus can be flexibly grouped to achieve different scene control and management. Compared with other dimming methods, the advantages and disadvantages of DALI dimming methods are as follows:
The advantages of DALI dimming:
1. Digital dimming, accurate, stable and smooth dimming;
2, DALI can communicate in two directions, and can feedback the status of the lamps to the system;
3, single lamp control, the control is more flexible;
4, DALI has strong anti-interference ability.
Disadvantages of DALI dimming:
1. The price of power supply is high;
2. Power debugging is more complicated;
3. It is necessary to increase the signal line and the wiring is complicated.
The DMX512 protocol was first developed from the USITT (American Theater Technology Association) into a console.
Use the standard digital interface to control the dimmer. 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 designed together with the power supply and the controller. 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.
The DMX512 receiver needs to set the address so that it can clearly receive the dimming command, which is 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 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.