The LED lighting is different with traditional lighting.LED is a basic pn-junction diode, which emits light when activated. If the power of LEDs is same, the current and voltage will be defferent because of adopting different brand leds. Because different LED light source has the different internal structure and distributed circuit, it leads to the every manufacturer of light source have different requirements of the dimmable led drivers.
So the LEDs are not compatible for dimming control system is the common problem in LED industry. In the meantime, the diversified LEDs face a higher challenge to dimming control system.
If the control system is not compatible for LED light fixtures, the LED lighting will appear to flicker or turning off. It also will damage the LED driver and light source.
Five kinds of Dimming Methods
1.Leading Edge Dimming
2.Trailing Edge Dimming
3.1-10V Dimming
4.DALI
5.DMX512
1.Leading Edge Phase Control Dimming
Leading edge dimming adopts Triac phase control methods to achieve voltage variations and lighting changes. When sinusoidal alternating current reaches 0 or a certain moment, add a shot pulse on the regulation of the thyristor control stage of TRIAC dimmer. Then the TRIAC dimmers can be turned on. After conduction, the change will remain for some time until the end of the half circle of sine current wave.
Leading edge dimmer have the advantages of high-adjusting accuracy,high efficiency,small size, light weight and easy to remote operation.It occupies a leading position in the market, and most of manufacturers produce this kind of dimmer.
Leading edge phase control dimmer adopts the silicon controlled rectifier as switch, so it is also called Triac dimmer. The advantage of FPC dimmer is low cost,compatible for existing circuit and no new line. The disadvantage is poor dimming performance.
2.Trailing Edge Phase Control Dimming
Trailing edge phase control dimmer adopts the FET or IGBT device. It usually use a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) switch, so it is also called MOSFET dimmer.
The MOSFET is behaving like a dimmer switch than an on-off switch.So the Triac dimmer can't be 100% shut off is nonexistent.
MOSFET dimmable circuit is more fit capacitive load dimming than Triac, but the MOSFET dimming is not developed because of high cost,complicated dimmable ciucuit and instability. So the Triac dimmer also occupies most of dimming system market.
Compared with leading edge dimmer, the trailing dege dimmer is applied to LED lighting fixtures. There is no
minimum load requirement, so it can achieve better performance from a single lighting fixture or very small load. But the MOSFET is rarely used in dimming system, it is usually made the rotary switch. This low power trailing edge phase control dimmer is not applied to engineering field.
Many lighting manufacturers use this dimmer to test their own dimmable led drivers and lighting fixtures. Then they promote they own dimmable products to engineering market. So the triac dimmable system is usually used for trailing edge dimmable led drivers in the project. The incompatible dimming method will cause the lighting flicker, and also will damage the led drivers and dimmer quickly.
3. 1-10V Dimming
1-10V dimming or 4-wire dimming uses an analog low-voltage signal to adjust the dim level of the attached load. Many load types, including fluorescent, metal halide, and LED, use this method of dimming. So 0-10V dimmer also can support a mass of LED lamp.
But the disadvantage of application is also obvious. The low-voltage signal need to add an extra circuit wiring, it will greatly enhance the requirement of construction.
4. DALI dimming principle
The DALI (Digital Addressable Lighting Interface) digital dimming method is an open protocol defined by the DALI standard. Wiring topology is simplified as up to 64 ballasts may be wired to the same control wire pair. Light sources wired to the same control pair may be separately controlled by commanding their unique addresses. Light sources may also be assigned to up to 16 groups so that they respond to a single command issued to the group address. This protocol allows for
bi-directional communication between the light source and the dimmer allowing for power monitoring, failure reporting and emergency lighting tests.
Broadcast DALI is a simplified approach that has the same control features as 0-10V dimming. In broadcast DALI, any DALI light sources wired to the same pair of control wires will respond to the same signals and to the same light intensity. Individual light source control or group control is not possible through broadcast DALI. The advantage of using broadcast DALI over the 0-10V method is that DALI is not subject to voltage drop over long wire runs. This allows the lamps to dim more uniformly.
5. DMX512
DMX512 (Digital Multiplex) is a standard for digital communication networks that are commonly used to control stage lighting and effects. It was originally intended as a standardized method for controlling light dimmers.
DMX512 transcends analog system, but it can't entirely replace anolog system. DMX512 will be chosen with its simplicity, reliability and flexibility if there is enough money to allow.
In a practical application, the control method of DMX512 is that the led driver and controller are designed together.
DMX512 controller can control 8-24 wires. But in the building lighting project, it requires to install a controller in 12 meters because of the weak DC wiring. And the control bus is parallel connection,so many wiring can't be implemented in many cases.
The receiver of DMX512 need to set up the address in order to receive the dimming instructions. But this is also inconvenient in the practical application.The lighting solution is complicated with multiple controllers, and the operational software also will be designed complicated. So DMX512 fit for the occasion that the lamp can be put together, such as stage lighting.
In conclusion, the main disadvantage of DMX controller is the special layout and type of wiring. It also need a certain programming in order to set up the essential color and scene, the cost of post-maintenance will be very expensive.