Principle of Three-stage Dimming of the Lamp_How to Use TRIAC to Dim the LED Lamp and How to Design

Principle of three-stage dimming of the lamp_How to use TRIAC to dim the LED lamp and how to design the specific scheme? - Programmer Sought

At present, non-energy-saving lighting dimming mainly uses TRIAC dimmers (triacs) for dimming, and TRIAC dimmers are also currently the most widely used dimmers. The working principle of the TRIAC dimmer is shown in Figure 1. The RC circuit connecting R1, R2 and C1 can delay the start of the TRIAC dimmer until the voltage of C1 rises to the trigger point voltage of the AC diode (Diac); The higher the resistance of the potentiometer (the sliding pointer slides downwards), the longer the start-up delay time. This can shorten the TRIAC dimmer's "on time" or reduce its "on angle" (Θ). Therefore, the average power supplied to the load can be reduced. TRIAC dimmers must continuously provide holding current (IH) to ensure that the circuit is always "on". According to Wu Zhimin, senior marketing manager for the Asia-Pacific region of National Semiconductor Corporation (NS), according to current industry design standards, in-wall TRIAC dimmers are usually connected to resistive loads such as incandescent lamps or halogen lamps. However, LED bulbs do not belong to the resistance load that the in-wall TRIAC dimmer can be connected to. Therefore, if the traditional in-wall TRIAC dimmer is used to control the brightness of the LED bulb, the control effect will not reach the best state. The current LED drivers on the market can produce flicker with a frequency of 120 Hz, or cannot achieve a dimming ratio of 100:1. However, if the TRIAC dimmer is completely replaced and a new dimmer is used to support LED dimming, cost will be a problem. Therefore, NS recently launched a LM3445 LED driver (Figure 2), which can support traditional in-wall TRIAC dimmers, which can stably control the brightness of high-brightness LEDs and ensure that no light flickering problems occur. LM3445 can not only support a dimming ratio of up to 100:1, but also output a constant current above 1A to drive multiple strings of LEDs, which makes it suitable for residential, building, commercial and industrial lighting applications and other fields. According to Wu Zhimin, due to the use of a constant current floating buck regulator control architecture, LM3445 can ensure that the ripple current of the input LED is constant, no matter how the input voltage fluctuates, and regardless of any deviation of the LED voltage (VLED) due to temperature changes This patented technology can ensure that the current flowing into the LED is constant, and the brightness of the LED lamp is uniform and stable during the dimming process, which helps to extend the life of the LED. LM3445 supports a working voltage range of 80V270V (AC). Its conduction angle detector/decoder can achieve a 100:1 dimming range. The device has a built-in 300Ω bleeder resistor, whenever the line voltage drops to a lower level , The bleeder will allow current to continue to flow so that the TRIAC dimmer can continue to operate normally. LM3445 can adjust the output current to 1A or even higher, and can adopt the control mode of the master/slave system to ensure the uniform brightness of the multi-channel lighting system. In addition, the chip has a built-in 230W voltage divider circuit and a passive power factor correction circuit, which can directly intercept the current from the line during most of the cycle, provide a constant positive voltage for the buck regulator, and ensure the lowest power consumption . In addition to LED dimmers, TRIAC can also be used in motor speed control, pressure control, and liquid level adjustment systems. In high-power AC applications, especially in the industrial and consumer electronics fields, its constant power control is very important. Constant power control is generally implemented by an algorithm. The most classic and commonly used algorithm is PID algorithm. Generally for TRIAC, we will combine PID algorithms, sensors, and corresponding control circuits to achieve constant power control by adjusting the TRIAC conduction angle in real time. Because many people do not understand and dare not use TRIAC to realize constant power circuit design, today I will bring you the following live class to explain the constant power realization method of PID algorithm based on TRIAC. The first 300 applicants can get free TRIAC application circuit materials *Tips:Sign up for the live broadcast before the start of the broadcast, and you will get the right to watch the video playback live PPT materials for free forever. Children's shoes who have not registered or overdue registration cannot watch the playback video. Please be aware!