The traditional analog circuit and PK resistance divider, digital control technology in LED why is more dominant in the light?

In this paper, SCOTT BROWN describes the LED lamp connected to the adjustable dimming light is tangent to the difficulty, and introduces the digital control technology can realize the basic properties of flicker in solid-state lighting applications.

Although the LED lamp is now a large number of sales, but this kind of solid-state lighting (SSL) product performance, especially in the light field will still be lower than traditional light bulbs. Indeed, the design for conventional drive LED replacement lamps to provide dimming performance, energy efficiency and reliability really satisfactory at the right price. However, the digital control drive in electronic devices can now remove the bleeder resistor unnecessary (used to enhance controllable silicon dimmer operation), while allowing a flicker free dimming to low light level.

The dimmer is already widely used in household lighting equipment, not only save energy, reduce electricity, also provides a comfortable and convenient. The use of energy-saving LED lighting, from the perspective of efficiency, light is not very important. However, at home, restaurants, entertainment or conference rooms and other places, it is easy to affect mood lighting. This requires smooth dimming, no flicker, covering a wide range of light levels.

In many applications, the ideal scene deployment of solid-state lighting is simply by using the same size of the LED lamps instead of incandescent lamp upgrade. This is because the user expects the new lamp with its existing dimmer can run perfectly, but the reality may be due to the type and quality of dimmer and different.

Dimmer operation

The standard tangential dimmer design based on triac for driving resistance provided by incandescent lamp load. Controllable silicon dimmer dimmer is also known as the frontier, because by using triac AC regulating each half wave conduction angle to change the sine wave to achieve dimming (Figure 1). Three terminal bidirectional thyristor switch delay conduction angle for lamp dimming.

Figure 1. the front adjustable and controllable silicon dimmer light delayed start, until the late cycle.

When applying a trigger pulse, if the current is maintained at the specified device to maintain the current above three terminal bidirectional thyristor switch, and remain in the remaining period of conduction. If the load is the incandescent light bulb, is easy to maintain in the current to maintain the current above threshold, so the three terminal bidirectional thyristor switch will maintain the conduction current decreases, until at the end of the cycle.

However, the two factors can limit the dimming range, even incandescent bulbs will have some impact. The dimming circuit usually consists of electromagnetic interference (EMI) filter, which comprises an inductor and a capacitor can be introduced into the current waveform of pulse noise components. If the inductor is low quality components, the noise can make current from connected to surge immediately below the three end of the bidirectional thyristor holding current, so that the device is closed, resulting in visible light flashing. Similarly, if you use a relatively low cost of the current three terminal bidirectional thyristor high, dimmer dimming level can be maintained.

Figure 2 compares currently on the market of 5 required light modulator based on triac minimum load current. Minimum peak current LED driver needs to absorb from the three terminal bidirectional thyristor switch, to ensure proper operation.

Figure 2. five different dimmer holding current.

LED load current

Run the dimmer challenges in low load current, when the load is LED to replace the light bulb, the challenge will intensify. Unlike incandescent lamp, LED is not a pure resistance. The impedance is reactive, so it can prevent the current increase, more than three terminal bidirectional thyristor holding current threshold, so that the devices in the trigger pulse conduction was maintained after removal. Low level light may also be difficult to achieve, because the power LED usually consumes less than incandescent bulbs. Therefore, the current phase of three terminal bidirectional thyristor development at the maximum dimming angle required may be very low. The current can be reduced to three terminal bidirectional thyristor switch to maintain minimum electric current, LED lights flashing or suddenly stop working.

In practice, dimmers require dimming level achieved more than people perceived. Because of the human eye by expanding the iris to compensate for the low light level, the relationship between the dimming effect so the electronic settings and perception for light is not linear. If the adjustment dimmer light will reduce to the maximum level measurement in 10%, is reduced by about 30% of the human eye can see. In order to achieve the perception of the dimming level 10%, dimmer must be able to reduce light level measurement to only 1%. Illuminating Engineering Society (IES) published the tenth edition of "lighting Handbook" records the relationship between light and measuring the light perception of the:

The perception of light = 100 * * (measuring light / 100)

LED replacement lamp manufacturers need to be able to guarantee different quality and cost of the three end of the triac dimmer can interoperability, and to ensure that no flashing lighting to low light levels, in order to maximize customer satisfaction.

Let the flow of current discharge circuit

A common solution is to add the discharge circuit to maintain sufficient current three terminal bidirectional thyristor switch in the dimming level low. This may be the use of passive circuit resistance, or the use of power transistor type discharge, for do not need to stop the current bleeder resistor.

The use of passive discharge device has two shortcomings. Due to continuous current through the resistor, so the efficiency advantage obtained by using the LED technology will be greatly reduced. More important is the impact of working life of the radiating lamp. Thermal management is very important for LED lights. The LED transmitter itself can work at high temperatures of 25000 to 50,0