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Principle of LED dimmer

There are three principles of LED dimmers
1. Pulse Width Modulation (PWM)
Digitize the square wave of the power supply and control the square wave's duty cycle to achieve the purpose of managing the current.
2. Constant current power regulation
The magnitude of the current can be easily adjusted with analogue linear technology.
3. Group control
Group multiple LEDs into groups and control them with a simple grouping device.

The above 1.2. Two methods can use the adjustable resistance knob for step-less control. Due to the maturity of the PWM module technology, the cost is reduced. It is difficult to determine which method of flow control is used in terms of price. However, the adjustable resistor itself is not a very reliable component. Often due to the ingress of dust or the inaccuracy of the manufacturing process, there will be an instantaneous jump when operating the adjustable resistor, and the light source will flicker. This kind of flicker is relatively unobvious when using the PWM mode, and it is more apparent when using linear technology to regulate the current.

Regardless of how the current is adjusted, it can be changed to a tact switch (Tact Switch) or an independent grouping switch (such as a grouper, a remote control) to control the lights. This kind of quality is more reliable, and the service life is much longer. It is essential to use adjustable resistors for delicate lighting control. It is recommended to use high-quality adjustable resistors (usually a few dollars).


Whether the LED is driven by a buck, boost, buck/boost or linear regulator, the most common thread connecting each drive circuit is to control the light output. Nowadays, only a few applications only need simple functions on and off, and most of them need to fine-tune the brightness from 0 to 100%. At present, in terms of luminosity control, the leading two solutions are linearly adjusting the LED current (analogue dimming) or switching the drive current from 0 to the target current value back and forth (digital dimming) at a high frequency that is invisible to the naked eye. Light). Using pulse width modulation (PWM) to set the cycle and duty cycle may be the easiest way to achieve digital dimming because the same technology can be used to control most switching converters.
PWM dimming can adjust accurate colour light


Generally speaking, analogue dimming is easier to implement, because the output current of the LED driver changes in proportion to the control voltage, and analogue dimming will not cause additional electromagnetic compatibility (EMC)/electromagnetic interference (EMI) potential frequencies problem. However, most of the reasons why PWM dimming is used in most designs are based on the essential characteristics of LEDs, that is, the displacement of the emitted light is proportional to the average drive current (Figure 1).

For monochromatic LEDs, the wavelength of the primary light waves will change, while for white LEDs, it is the relative colour temperature (CCT) that varies. It is difficult for the naked eye to detect the change in nano-wavelength in red, green or blue LEDs, significantly when the intensity of the light is also changing, but the difference in the colour temperature of white light is easier to detect. Most white light LEDs contain a wafer that emits photons in the blue spectrum.

These photons will emit photons in the visible light range after hitting the phosphorescent coating. At lower currents, phosphorescence will become dominant and bias the light toward yellow; while at higher currents, the LED emits more blue light, which favors the light toward blue, and at the same time produces a higher CCT. For applications that use more than one white LED, the CCT difference between two adjacent LEDs will be prominent and visually unpleasant. This concept can be further extended to light sources that mix multiple monochromatic LED lights. Once there is more than one light source, any difference in CCT between them will be dazzling.