What is LED stepless dimming?

Stepless dimming: "level" means "shift". Stepless means continuous change, not abrupt change or step-by-step, and it is sloped rather than stepped. If it involves the use of a unique digital stepless dimming system technology, users only need to rotate the lamp head to customize the brightness setting. There are three principles of LED dimmers:

The first type: Pulse Width Modulation (PWM for short) digitizes the square wave of the power supply and controls the duty cycle of the square wave to achieve the purpose of current control.

The second type: constant current power supply regulation. The current can be easily adjusted by analog linear technology.

The third type: group control group multiple LEDs and control them with a simple grouper

Application of LED stepless dimming

1. Analog DC dimming <Use analog signal to control the output DC current of the power module>

Analog DC dimming generally uses analog level signals to change the reference of the LED driver's steady current control loop to control the output DC current, thereby effectively controlling the brightness of the LED lamp. The control of this dimming method is simple to implement, does not need to change the main circuit structure of the original constant current driver, and the driver has low cost and high efficiency. When the LED is driven by a constant current source, the current drops and the LED conduction voltage also decreases, and the luminous efficiency is high. This brightness control method has been applied in the stepless dimming control of some highway and tunnel LED lighting.

Since the 0-10V dimming power supply is connected to 220V alternating current, and the 0-10V dimmer has manual contact, it is necessary to achieve electrical isolation between the two. Therefore, it is the isolation module that needs to place a 0-10V voltage inside the 0-10V dimming power supply, and the PWM signal is a commonly used isolation technology to achieve isolation while taking into account the transmission of analog information. Traditionally, the common method used to realize the detection of analog quantity and the isolated output of PWM signal is to realize the function through the circuit composed of op amp, MCU and discrete devices, which often requires more than 30 components, the system is redundant, accurate and reliable Sex is often bad.

Therefore, this application is often replaced by a single-chip solution. It can solve many problems of the traditional analog signal to PWM scheme, high precision, adjustable speed, no need to write programs, and the system is stable and reliable.

2. PWM dimming (the secondary side adopts PWM control to control the effective value of the output current)

This control mode is generally based on a DC constant voltage power supply, plus a constant current DC/DC converter that can achieve fast current control (or a PWM chopper switch is added to the output of the constant current power supply). Usually a chopping frequency of several hundred Hz to 1KHz controls the working time of a constant current DC/DC converter (or PWM chopping switch) in a unit cycle, so as to obtain square wave output currents with different duty cycles and adjust the square wave output The duty cycle of the current is to adjust the average value of the output current, thereby changing the brightness of the LED light. Using PWM mode dimming, when the chopping frequency is above several hundred Hz, the human eye will not feel flicker or jitter.

One advantage of LED PWM dimming is that the light color of the light source does not change with the current. This control method adds a DC/DC converter to the original constant voltage source (or adds a PWM chopper switch to the original constant current source), increases the cost of the circuit, and increases the cost of the main circuit. loss. Under the same average current, the luminous efficiency of the LED light source under the PWM square wave current is lower than that under the direct current, so the energy-saving effect of the PWM dimming method is worse than that of the analog dimming.

3. Current-limiting mode dimming (current-limiting control through transistors as variable resistors)

Current limiting mode dimming is to connect LED lights and transistors in series in the output of the DC constant voltage source module. The transistors work in the amplifying area as a variable current limiting resistor. The LED current can be effectively controlled by changing the resistance of the variable resistor. The brightness of the LED lights. In this dimming mode, the voltage and current that the transistor bears are consumed in the form of heat, and the LED driving efficiency is low. This control method is only suitable for the brightness control of low-power LEDs.

Induction lamp continuous dimming

Induction lamp, also known as electromagnetic induction lamp (INDUCTIONLAMP), is composed of three parts: ballast, coupler and glass bulb (tube). Due to different operating frequencies, it can be divided into high-frequency electrodeless and low-frequency electrodeless lamps. The high frequency induction lamp mainly adopts the bulb type internal coupling mode, and the working frequency is 2.65MHz; the low frequency induction lamp mainly adopts the tube type and ring external coupling mode, and the working frequency is 250KHz.

The structure of the induction lamp is roughly composed of three parts, a high-frequency electronic ballast, a power coupler (internal coupling, 2.65MHZ) and a glass bulb coated with rare-earth phosphors (it can be of various shapes. Type, square, etc.). The ballast generates a 2.65MHz high-frequency sinusoidal voltage under the action of the mains power (50HZ), and at the same time generates an ignition voltage of about 3000V, which is instantly established in the glass bulb coated with rare-earth phosphor through the power coupler The high-frequency magnetic field, the high-frequency magnetic field and the high-frequency alternating electric field at the same time, cause the inert gas (mixed gas of krypton and argon) inside the bulb to ionize and then produce the avalanche effect (should be a university physics, semiconductors Chapter 1, Zener breakdown and avalanche breakdown), which produce a lot of ultraviolet radiation. Phosphors produce visible light under the action of ultraviolet rays.

The working voltage of the induction lamp works normally within the range of AC 85V-275V, and the DC can be customized and dimmable. Because of the use of electronic ballasts, the AC and DC and voltage ranges are wide, and continuous dimming can also be achieved. This is impossible with metal halide lamps.