Guide: LED dimmer is an LED electrical device that changes the luminous flux of the light source in the illumination device and adjusts the illumination level. The purpose of the LED dimmer is to adjust the brightness of the light. By reducing or increasing the RMS voltage, the average power of the light produces a different intensity of light output. While variable voltage devices can be used for a variety of purposes, this regulation is intended to control illumination. The following small series will introduce the LED dimming technology and LED dimming problems.
LED dimming technology:
In today's LED industry, I am most optimistic about LED dimming technology and LED driver power. The LED driver power supply is mainly oriented to the LED street light power supply. This time we mainly talk about LED dimming technology. LED dimming technology mainly has the following types:
1: SCR dimming is a dimming technology developed in incandescent lamps. Because incandescent lamps are purely resistive loads, thyristor chopper technology can be used to achieve dimming smoothly, but it is not practical for LEDs. Compatible with thyristor dimming power supply, usually low efficiency, 80% is difficult to achieve, which is contrary to the original intention of LED energy saving, and secondly, it is difficult to achieve high power factor, again, can only work in a single input voltage Under the circumstance, this dimming technology will die out due to the demise of incandescent lamps, but it will exist for some time due to the high market penetration rate.
2: Linear dimming utilizes the special dimming foot of the constant current chip to adjust the current of the LED to achieve the purpose of dimming. This technique works well, but the wiring is complicated, which is not conducive to the illumination of fluorescent lamps and the like. Many of the lamps use this method.
3: PWM dimming This method is similar to linear dimming, and together with linear dimming occupies most of the dimming table lamps. This PWM dimming user and customer is also very happy.
4: Remote control dimming is divided into infrared remote control and wireless remote control. It is more complicated to implement, but it can achieve the effect that color temperature, color and other dimming methods can not be achieved. It is mainly used for panel light dimming, and some bulbs. Use some dimming methods.
5: Segment dimming This dimming method achieves the purpose of dimming by switching the switches on the wall within a specified time. The advantage of this method is that no additional dimming components are required, and each lamp is installed according to the existing installation method. Dimming can be realized. In addition, since the dimming is completely controlled by the power switch chip, high efficiency and high power factor can be realized in the full voltage range regardless of the brightness at work. The disadvantage is that it can only be used in advance. The set brightness cycle adjustment can not achieve stepless dimming, and there are few types of such ICs, and the current adjustment rate is not satisfactory, but I think IC manufacturers will be more home-long as the technology matures. Perfect, personally feel that this dimming technology will become the mainstream of future dimming technology.
What is wrong with LED dimming:
LED lamps used to replace standard incandescent lamps typically contain an array of LEDs to ensure uniform illumination. These LEDs are connected together in series. The brightness of each LED is determined by its current. The forward voltage drop of the LED is approximately 3.4 V, typically between 2.8 V and 4.2 V. The LED string should be driven by a constant current source and the current must be tightly controlled to ensure a high degree of matching between adjacent LEDs.
In order to achieve dimming, the LED lamp must be able to analyze the variable phase angle output of the thyristor controller in order to unidirectionally adjust the constant current flowing to the LED. It is very difficult to do this while maintaining the dimmer's normal operation, often resulting in poor performance. The problem can be manifested as slow start-up, flicker, uneven illumination, or flicker when adjusting the brightness. In addition, there are problems such as inconsistencies between components and unwanted audio noise emitted by LED lamps. These negative conditions are usually caused by false triggering or premature shutdown of the thyristor and improper control of the LED current. The root cause of false triggering is current oscillations when the thyristor is turned on.
When the thyristor is turned on, the AC mains voltage is applied to the LC input filter of the LED lamp power supply almost simultaneously. A voltage step applied to the inductor can cause oscillation. If the dimmer current is below the thyristor current during the oscillation, the thyristor will stop conducting. The thyristor trigger circuit charges and then turns the dimmer back on. This irregular multiple thyristor restart enables the LED lamp to produce unwanted audible noise and flicker. Designing a simpler EMI filter helps reduce such unwanted oscillations. To achieve successful dimming, the input EMI filter inductor and capacitor must also be as small as possible.
The worst condition of the oscillation is represented by a 90 degree phase angle (when the input voltage reaches the sine wave peak, which is suddenly applied to the input of the LED lamp) and is a high input voltage (at this time, the dimmer's forward current is at a minimum Level). Premature shutdown occurs when deep dimming is required (such as a phase angle approaching 180 degrees) and a low input voltage. To reliably reduce luminosity, the thyristor must be monotonically turned on and stay at a point where the AC voltage drops to almost zero volts. For thyristors, the holding current required to maintain conduction is typically between 8 mA and 40 mA. Incandescent lamps are easier to maintain at this current level, but for LED lamps that consume only 10% of the equivalent incandescent lamp, this current can be reduced below the thyristor holding current, causing the thyristor to turn off prematurely. This can cause flicker and/or limit the dimming range.
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