One of the factors hindering the LED lighting is widely used, is them with the previously installed cutting phase (phase-cut) of bad matching performance between the dimmer.
According to the NEMA (National Electrical Manufacturers Association) data, only in North America, on the installation of a 150000000 household phase cut dimmer -- a device for incandescent lamp. The thermal inertia of the incandescent light bulb inherent obscures the unwelcome characteristics of dimmers are. On the contrary, LED lighting, especially in the power supply circuit or drive circuit, struggled to cope with these phase cut dimmer is constantly changing and unstable output market. Between the lamp and the lamp of the resulting large range between, and even dimmer and dimmer changes, and these to the user is not acceptable, although the design of driving circuit for realizing adaptive can alleviate this problem.
At first, the phase cut dimmer is as a kind of method is simple, efficient and cheap is designed for incandescent lamp light source brightness adjustment. It provided by restriction to the load power to achieve the dimming, allow only the AC network each half of the week on a certain percentage of the time is in a conducting state. By changing the dimmer position, will be able to change the cycle of conduction, thus controlling the power applied to the load, the ultimate realization of the light output change.
The phase cut dimmer
At present, there are two different types of phase cut dimmer (Figure 1). Front cutting phase modulation trigger angle optical delay after the zero crossing point (firing angel), the initial portion of each half cycle of AC excision, and only let the back part of the conduction. Trailing edge dimmer is working in the opposite way, in each half cycle of the alternating current the initial part of the conduction, while at the back part of the cut-off. Frontier dimmer use only one active device - three terminal bidirectional silicon controlled switch element, which makes their cost is very cheap, and therefore occupies a dominant position throughout the North American market.
A factor which causes the difference of LED lamp performance is the phase cut dimmer produced the maximum and minimum trigger angle exists great difference. Different suppliers, as well as the different product models, the trigger angle range is very large. Thus, the conduction time and applied to the load power may change.
The article by okorder.