LED lighting will replace the mainstream incandescent lighting and other lighting technology, a leading market position. However, the old technology to new technology conversion will take years. In the meantime, the challenges faced by designers of LED lights is how to ensure that the new design compatible with the existing controller originally developed for incandescent lighting and wiring architecture and reliable. Described in this article is the solution for low power and high power LED lighting systems, it is proven, very mature.
The structure of the LED light bulb
LED lights contain a dozen or more LED 200W chips, they are usually connected in series. The brightness of each chip size through which the current decision. As a result of the series connection, each LED chip of the light bulb will automatically by the same current, but vary the voltage on each chip. LED forward voltage drop is typically 3.4V, but it will change between 2.8V to 4.2V. Classification to limit the voltage fluctuation, but this would increase costs, and the forward voltage drop will continue to change with temperature and usage time of the LED. To provide a consistent light output, LED lights must be strictly regulate the efficient constant current power supply drive. LED light as incandescent alternatives, the power must be integrated in the lamp shell.
The typical integrated LED lamp drive circuit, LED 400W cluster, as well as for both the driver and LED chip to provide mechanical protection and thermal shell.
LED driver is very demanding. It must be energy efficient, you must meet stringent EMI and power factor specifications, and can safely tolerate a variety of fault conditions. One of the most difficult one of the requirements is to have a dimming function. Because there is a mismatch between the characteristics of the LED lights designed specifically for incandescent dimming controller, can easily lead to poor performance. The problem may be the performance of slow start, blinking, uneven illumination, or adjusting the brightness flicker. In addition, there is that each unit of performance is inconsistent, and LED lamps emit audible noise and other issues. These negative conditions are usually caused by the false triggering or premature shutdown controller and LED current control inappropriate.
Dimming controller
Lighting controller to a line dimming or PWM dimming. The simple line dimming the forefront of SCR controller. This is the most commonly used lighting control, but unfortunately, the use of SCR controller dimming of the LED Blue 150W will produce a large number of problems. The more advanced line dimmer Electronic Frontier or trailing edge dimmers. PWM dimmer is used in professional lighting systems.
Use cutting-edge SCR dimmers, dimming control is achieved by changing the thyristor conduction through the phase angle of each half cycle. Phase angle as a function of input power of the lamp and dimming signal, the phase angle range between close to 0 ° to 180 °.
One of the important parameters of the SCR holding current (IH). This is the SCR gate drive must be maintained to keep the conduction minimum load. In order to maintain the stable operation of the SCR, the current can not be zero, and the typical value of IH between 8mA to 40mA. Therefore, the phase angle of incandescent dimmers usually have a specified minimum load, 230V nominal AC voltage is typically 40W. This is to ensure that the current through the internal SCR is always higher than the current threshold for the maintenance of. To maintain the current very low power consumption LED lighting will become a problem.