How to use TRIAC to dim LED lights, and how to design the specific scheme?

How to use TRIAC to dim LED lights, and how to design the specific scheme?

At present, the dimming of non-energy-saving lighting mainly uses TRIAC dimmers (triacs) for dimming, and TRIAC dimmers are also the most widely used dimmers at present. The working principle of the TRIAC dimmer is shown in Figure 1. The RC circuit connecting R1, R2 and C1 together can delay the startup 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 further the slide pointer slides down), the longer the start-up delay. This reduces the “on time” or “conduction angle” (Θ) of the TRIAC dimmer. Therefore, the average power available to the load can be reduced. TR

At present, the dimming of non-energy-saving lighting mainly uses TRIAC dimmers (triacs) for dimming, and TRIAC dimmers are also the most widely used dimmers at present. The working principle of the TRIAC dimmer is shown in Figure 1. The RC circuit connecting R1, R2 and C1 together can delay the startup 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 further the slide pointer slides down), the longer the start-up delay. This reduces the “on time” or “conduction angle” (Θ) of the TRIAC dimmer. Therefore, the average power available to the load can be reduced. TRIAC dimmers must constantly provide a holding current (IH) to ensure that the circuit is always “on”.

How to use TRIAC to dim LED lights, and how to design the specific scheme?

Wu Zhimin, senior marketing manager of the Asia-Pacific region of National semiconductor Corporation (NS), said that according to the current industry design standards, in-wall TRIAC dimmers are usually connected to resistive loads such as incandescent lamps or halogen lamps. However, LED bulbs are not a resistive load that can be connected to in-wall TRIAC dimmers. Therefore, if the traditional in-wall TRIAC dimmer is used to control the brightness of LED bulbs, the control effect will not be optimal. Current LED drivers on the market produce flicker at 120Hz, or fail to achieve a 100:1 dimming ratio. However, if the TRIAC dimmer is completely replaced with a new dimmer to support LED dimming, cost will be an issue.

How to use TRIAC to dim LED lights, and how to design the specific scheme?

Therefore, NS recently launched an LM3445 LED driver (Figure 2), which can support traditional in-wall TRIAC dimmers, and can stably control the light and dark of high-brightness LEDs to ensure that there is no light flickering problem. The LM3445 can not only support a dimming ratio of up to 100:1, but also output a constant current of more than 1A to drive multiple strings of LEDs, which makes it suitable for many fields such as residential, building, commercial and industrial lighting.

Wu Zhimin introduced that due to the constant current floating buck regulator control architecture, the LM3445 can ensure that the ripple current of the input LED is constant, no matter how the input voltage fluctuates, and no matter how the LED voltage (VLED) changes due to temperature changes. , This patented technology can ensure that the current flowing into the LED is constant, ensuring that the brightness of the LED lamp is uniform and stable during the dimming process, which helps to prolong the life of the LED.

The LM3445 supports an operating voltage range of 80V to 270V (AC), its conduction angle detector/decoder can achieve a 100:1 dimming range, and 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. The LM3445 can adjust the output current to 1A or even higher, and can be controlled by a master/slave system to ensure uniform brightness in a multi-channel lighting system. In addition, the chip has a built-in 230W voltage divider circuit and passive power factor correction circuit, which can directly cut current from the line most of the time in 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 AC high-power applications, especially in the fields of industrial and consumer electronics, its constant power control is very important.

Constant power control, generally we use an algorithm to achieve, the most classic and most commonly used algorithm is the PID algorithm. Generally, for TRIAC, we will combine PID algorithm, sensor, and corresponding control circuit to realize constant power control by adjusting the conduction angle of TRIAC 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.

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