LED five dimming methods detailed explanation

169 views admin 2024-03-07

The luminous principle of LED is different from that of traditional lighting, and the LED light source with the same power is different because of the chip it uses, the current and voltage parameters are different, so its internal wiring structure and circuit distribution are different. The manufacturers of the light source on the adjustment of the optical drive requirements are not the same, so the control system and the light source electrical mismatch has become a common problem in the industry, while the diversification of LED also put forward a higher challenge to the control system, if the control system and lighting equipment is not matched, may cause the light to go out or flash, and may cause damage to the LED drive circuit and light source.

The DALI standard has defined a DALI network, consisting of a maximum of 64 units (which can be individually addressed), 16 groups, and 16 scenes. Different lighting units on the DALI bus can be flexibly grouped to achieve different scene control and management. In practice, a typical DALI system application can control 40 to 50 lights, which can be divided into 16 groups, while being able to handle some controls/scenarios in parallel

The advantage of DALI is that it has a special protocol to enhance product interoperability between different brands, and each DALI device has a separate address code, which can truly be controlled by a single lamp. Two-way communication, easy to query and understand the equipment status and information in time.

Thyristor dimming has been applied to incandescent lamps and energy-saving lamps earlier, and is currently the most widely used dimming method for LED dimming.

Thyristor dimming is a kind of physical dimming, starting from AC phase 0, the input voltage is chopped, until the thyristor is on, there is no voltage input.

The working principle is to generate a tangential output voltage waveform after the input voltage waveform passes through the on-angle cutting wave. Using the principle of tangential, the effective value of the output voltage can be reduced to reduce the power of the ordinary load (resistance load).

Thyristor dimmer has the advantages of high adjustment accuracy, high efficiency, small size, light weight, easy remote control, etc., which occupies a dominant position in the market.

The technique of PWM Pulse Width Modulation is to control the analog circuit through the on-off control of the inverter circuit switch. The output waveform of the pulse width modulation technique is a series of pulses of equal size, which are used to replace the desired waveform.

Take sine wave as an example, that is, the equivalent voltage of this series of pulses is sine wave, and the output pulse is as smooth as possible and has less low-order harmonics. According to different needs, the width of each pulse can be adjusted accordingly to change the output voltage or output frequency equivalent, and then achieve the control of the analog circuit. In short, PWM is a method of digitally encoding analog signal levels.

Through the use of high-resolution counters, the occupancy ratio of the square wave is modulated to encode the level of a specific analog signal. The PWM signal is still digital because at any given moment, the full amplitude of the DC supply is either completely present or completely absent. A voltage or current source is added to the analog load in a sequence of repeated pulses on or off. When the DC power supply is added to the load, when the power supply is disconnected.

If the frequency of light and dark is more than 100Hz, the human eye sees the average brightness, rather than the LED flashing. PWM adjusts the brightness by adjusting the time ratio of light and dark, in a PWM cycle, because the brightness perceived by the human eye for the light flicker greater than 100Hz is a cumulative process, that is, the greater the proportion of the light time in the whole cycle, the brighter the human eye feels.

The 0/1-10V dimming device has two independent circuits, one is an ordinary voltage circuit, which is used to turn on or off the power supply to the lighting device, and the other is a low-voltage circuit, which provides a reference voltage to tell the dimming level of the lighting device.

1-10V is only the dimmer is 1-10V, when the resistance dimmer is adjusted to the minimum 1V, the output current is 10%(non-fixed value), if the output current is 100% at 10V, the brightness will also be 100%.

DMX stands for Digital MultipleX, which means multiplex digital transmission. DMX512 is a standard protocol for digital communication networks, often used to control stages and effects.

Compared with the traditional analog dimming system, the digital lighting system based on DMX512 control protocol can provide powerful control functions for large and medium-sized indoor and outdoor LED lighting systems.

The signal transmission mode is RS485 differential signal transmission, and the data transmission is based on an 8-bit asynchronous serial protocol with one start bit (low level) and two stop bits (high level), and no parity check. So a data frame has 11 bits, and since the width of each bit is 4us, it takes 44us to send each frame. The transfer rate is 250kbps.