Dimming of LED with traditional TRIAC dimmer

At present, the non energy saving lighting dimming is mainly using TRIAC dimmer (three terminal triac) dimming, TRIAC dimmer is currently the most widely used dimmer. TRIAC dimmer working principle as shown in Figure 1, RC R1, R2 and C1 circuits are connected together can make TRIAC dimmer delay start, voltage up to C1 up to touch the AC diode (Diac) trigger voltage; the potentiometer resistance is high (sliding pointer down more slip), start the delay time is long. Reduce or "lead time" that can shorten the TRIAC dimmer the conduction angle (theta) ". Therefore, the average power supply can be reduced. The TRIAC dimmer must provide a constant current (IH) to ensure that the circuit is always in the "on" state.

National Semiconductor Corporation Ns (NS) senior manager of the Asia Pacific region, said Wu Zhimin, according to the current industry design standards, into the wall type TRIAC dimmer is usually connected incandescent or halogen lamps such resistance load. However, LED bulbs do not belong to the wall type TRIAC dimmer can access the resistive load, so if the use of the traditional wall type TRIAC dimmer to adjust the brightness of the LED bulb, the control effect will not reach the best state. At present, the LED drive on the market will produce a flicker frequency of 120Hz, or can not reach the dimming ratio of 100:1. However, the cost will be a problem if the TRIAC dimmer is completely replaced and a new dimmer is used to support the LED dimming.

Therefore, NS recently launched a LM3445 LED driver (Figure 2), which can support the traditional wall type TRIAC dimmer, can be stable control of high brightness LED light dark, to ensure that there will be no light flashes. LM3445 can not only support up to 100:1 dimming ratio, but also the constant current to drive the output string LED above 1A, which can be used in residential, commercial and industrial buildings, special lighting and other fields.

Wu Zhimin, due to the constant current control architecture floating step-down regulator, LM3445 can ensure the constant input ripple current LED constant, regardless of how the input voltage fluctuation, regardless of the LED voltage (VLED) due to temperature change and any offset, this patented technology can ensure that the constant current flows into the LED invariant, ensure LED lights in in the process of adjusting light brightness uniformity and stability, which helps to prolong the life of LED.

LM3445 support 80V ~ 270V (AC) working voltage, the conduction angle of the detector / decoder can achieve 100:1 dimming range, the device built-in 300 bleeder resistor, when line voltage down to the low level, discharge device will allow current continues to flow, so that the TRIAC dimmer can continue normal operation. LM3445 can adjust the output current to 1A or even higher, the main / slave system can be used to ensure the uniformity of multi-channel lighting system. In addition, the circuit chip built-in 230W divider and passive power factor correction circuit, most of the time in the period can be directly from the line interception current positive voltage constant for buck regulator, and ensure the lowest power consumption.