Details about TRIAC dimming LED lighting technology

　　In recent years, with the rise of the global LED commercial lighting markets, in China, including many LED manufacturers have the LED commercial lighting products in an important position on the market development. Especially due to the recent Japan, Europe and the United States and other major market for LED lighting products for their high efficiency, long life, high power factor, flexible expansion, dimmable and other requirements, making the LED driver IC and power industry is facing a new revolution . Therefore, in the next two years, smart dimming LED lighting applications, especially in the proportion of commercial lighting is expected to increase rapidly.

　　According to the survey analysis report, the US market is a greater demand for dimming products, almost 100% of all dimming products. European markets a little less, but also accounted for a large proportion. In addition, the intelligent LED bulbs this year there may be a large-scale commercial. And the vast majority of which are in line with the product dimming TRIAC dimmers use. Therefore, study of SCR dimming LED lighting products, it is meaningful.

　　1 SCR dimming Profile

　　Analysis of the traditional incandescent, halogen and other dimming system, as compared with LED lights, incandescent and halogen lamps are purely resistive devices, which means that it is always current and voltage waveforms are the same when using available when silicon to control dimming, input voltage waveform due to changes in the angle of thyristor deviate sine wave, which is changing the input voltage rms, you can achieve the purpose of dimming.

　　SCR with a switch in the potentiometer, connected to n input terminals for controlling the light switch. Thyristor process, changing its internal adjustable resistor divider ratio, changing its conduction angle, you can change the output voltage RMS, enabling dimming function. In addition to the SCR, as well as cutting-edge transistor trailing edge dimming technology, the basic principles are the same.

　　2, SCR dimming shortcomings and problems

　　When using SCR dimming, or will there is a range of issues.

　　(1) dimming process, with the conduction angle of the internal changes in the input voltage sine wave is thyristor destroyed, thereby reducing the power factor (PF), PF is usually less than 0.5, and at the dimming time, with the smaller the conduction angle, power factor and more low (only 0.25 1/4 brightness).

　　(2) As above, the input voltage sine wave was destroyed, non-sinusoidal waveforms increased harmonic coefficients.

　　(3) LED driver circuit input non-sinusoidal voltage waveform on the line will cause serious interference signals (EMI).

　　(4) Dimming process at low load is very easy to maintain because of the current lack of instability phenomenon, solutions must be combined with a bleeder resistor. Typically the bleed resistor to consume at least 1-2 watts of power, which reduces the efficiency of the constant current source circuit.

　　(5) When using SCR dimming for incandescent dimming circuit, when the input LC filter and SCR oscillation due to the thermal inertia of the incandescent lamp, the human eye could not see this oscillation. And when the triac dimmer circuit with LED drive circuit supporting the use, will produce audible noise and flicker, which is often unacceptable.

　　3, SCR dimming advantage

　　Lighting market development so far, although there are many SCR dimming shortcomings and problems, however, because of its long history, the technology is mature and stable, as well as halogen and incandescent lamps have the perfect combination, account for a large transfer optical market. Dimming place in most regions, which have been installed SCR dimming of incandescent or halogen place, consumers have been installed on the walls of the two leading lighting connecting wires, and also on the wall installation of SCR dimmer switch boxes and knobs. For consumers, if we can simply replace incandescent or halogen lamp on, without having to replace the thyristor switch on the wall or another to increase the number of cables, it is a relatively simple program, but also compare as a general practice can be accepted by consumers. This means that LED lighting products really if you want to completely replace incandescent and halogen lamps and thyristor dimmers dimmable applications, it must be compatible with the SCR dimming light. This is also a challenge to develop LED driver IC designer of the common face. How for SCR dimming and LED Special drive to develop a suitable IC seemed so important.