NXP可调光LED灯具设计指南

近几年，由于LED灯具的出现，照明行业见证了一场新的革命，在零售商那，白炽灯已经成为另一个时代，在新的市场上紧凑型节能灯必须与新成员竞争。LED照明的出现有很多原因。LED技术在持续的发展，并且在迅速的增长，LED更亮更节能。再加上高效率，这些特征使LED成为理想的照明产品。一个白炽灯大约光效大约是10lm/w,而LED可以达到100lm/w,LED和目前市场上的紧凑型节能灯相比已经更高效。

生态问题和公众越来越相关，随着全球变暖和气候变更意识的增强，节约资源和能源的思想已经在市场战略中成为重要的特征。过去十年制造商们同心协力减少摩托车燃料的消耗，结束100W白炽灯生产和零售，完美的表现了这一趋势。政府也转向这个方向，通过减少税收和财政鼓励来支持这个环境友好产品，通常被称为节能产品。

LED还有许多其他的优势，包括：高调光性、寿命长、小型化等。根据形状、颜色、和创造氛围不同为照明应用提供很多新的视角。

然而，目前LED消费市场由改造灯组成，规定满足以下要求：

必须采取一些措施确保和已经存在的住房约束兼容，特别是使用调光器时

外形尺寸必须和爱迪生灯具保持一致

LED产生的热必须被分散掉

Until now, control equipment for home lighting has been based on the incandescent lamp.The most economical way to provide dimming functionality was to use AC mains phase-cut dimmers. These dimmers were developed to be used with an incandescent lamp that can be regarded as a resistive load.

The equivalent load of new electronic light sources such as CFL or LED lamps, is no longer purely resistive. This makes a considerable difference in the way the dimmer works. Using an unsuitable load can lead to unsatisfactory functioning of the system. It can create some very unpleasant flickering of the light, or even damage the lamp or dimmer. This can be a disappointment to customers, and after such an experience, a negative opinion about the product can prevail. Moreover, dimmers are still quite expensive, and customers cannot be expected to change their dimmers in order to suit their new lamps. Consequently, dimmer compatibility is a very important feature of the next generation of LED based products.

There are various types of phase-cut dimmers, but they all use the same principle i.e.cutting a part of the mains sine wave during each period. This is achieved using a switch.When the switch is conducting, a supply is delivered to the load (the lamp). When it is off,no supply is delivered. The total energy delivered is modulated by adjusting the conduction time.

There are two types of dimmers: leading edge and trailing edge types.

• Leading edge dimmers - the phase is cut at the beginning of the mains half period.After a time corresponding to the dimming position, the switch is set to “on” and the supply is delivered until the end of the half period. After crossing zero, the operation is
repeated。

• Trailing edge dimmers - the switch is set to “on” at the beginning of the half period,”
and closed after a time corresponding to the dimming position. It stays off until the end
of the half period. After crossing zero, the operation is repeated。


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