recolux helps you quickly understand what LED lights are缩略图

recolux helps you quickly understand what LED lights are

A: What is LED

Light source after incandescent, fluorescent, to the LED development process, LED has a low energy consumption, high brightness, non-mercury and non-toxic, long life, instantaneous start, plasticity and other advantages, has replaced the traditional light source, in this article does not do too much reiteration of the traditional light source.

The so-called LED that light-emitting diode, is a semiconductor light-emitting material, when the two ends plus forward voltage, the carriers in the semiconductor compounding caused by photon emission and produce light.LED can directly emit red, yellow, blue, green, green, orange, purple, white light.

recolux helps you quickly understand what LED lights are插图

SMD Chip Beads
Second: the structure of LED lamp beads

LED lamp bead structure diagram
1, a LED light source by the bracket, chip, glue, phosphor, wire Composition

2, LED bracket is generally made of copper (also iron, aluminium and ceramics, etc.), because the copper conductivity is very good, it will be inside the lead, to connect the led lamp bead internal electrode.

3, high-end light source wire are used 0.999 pure gold wire, diameter: 0.8mil, 1.0mil. some of the pursuit of low-cost manufacturers with copper-doped alloy wire to do.

4, phosphor is to play the role of regulating the colour temperature of the light source .

5, common high-end chips are: U.S. CREE (Corey), Bridgelux (Pratt & Whitney); Japan Nichia (Nichia), Germany Osram Osram; Taiwan: Epistar.

Epistar &CREE
Low-end chips: wide crop, Tai Valley, light macro, the new century, light, Baihong, light lei; Mainland China: Woodland, Xiamen, Sanan, Shanghai, Shanghai Blu-ray, Shilan Ming core, Dalian Lumi ……. (Mainland China is now mainly used in Taiwan chips)

LED lamp bead encapsulation after the formation of the lamp bead can be removed from the bracket, the lamp bead two copper feet that became the positive and negative poles of the lamp bead, used for welding to the LED lamps and lanterns or other LED products.

Third: common LED light source

The market often circulate LED models are 2835, 5050, 5730, 5630, 3030, 4040, 7030 and integrated COB and high-power lamp beads, distinguish between the light source model is to patch the length and width of the name, SMD SMD as an example of the following picture for the 2835 patch, that is, the width of 2.8 length of 3.5, this type of light source is commonly used in the LED light bulbs, downlights, spotlights, ceiling lamps, light bands, tubes and so on. Light tubes and so on. Each power about 0.1W-1W.

recolux helps you quickly understand what LED lights are插图2

SMD2835 SMD
High-power lamp beads are commonly used in spotlights and outdoor lamps and lanterns, such as 1W, 2W, 3W each.

High-power LED beads
COB integrated light source is common 5-50W each, commonly used in spotlights, track lights and floodlights and other high-power lamps and lanterns.

COB integrated light source
Four: often said that the LED parameter indicators

1, colour temperature: light contains colour components of a unit of measurement, unit K (Kelvin), the smaller the value of the colour is more red, the larger the value of the colour is more blue, the middle value of the white, the normal use of the light colour range of about 3000K-6500K, i.e., the warm white light and white light, the most popular neutral light is now about 4000K, (poor-quality light sources are very large colour difference, common warm white light reddish, blue) (The colour difference of inferior light source is very big, commonly warm white light is reddish, positive white light is bluish)

Colour temperature comparison table

  1. luminous efficiency: the luminous flux emitted by the light source and the ratio of power consumption, called luminous efficiency, the unit is lumen LM / W (lumens / watt). Different light sources emit the same luminous flux, the less power consumed, the higher the luminous efficiency .
  2. Brightness: defined as the brightness of the light source unit, that is, the luminous intensity per unit of projected area. The unit of brightness is candela / square metre (cd / m2) brightness is the human perception of the intensity of light. It is a subjective amount.

4, illuminance: refers to the luminous flux of visible light received per unit area. Unit lux (Lux or lx). Used to indicate the intensity of light and the surface area of the object is the amount of illumination.

Illumination diagram
5, colour rendering index: (the simplest understanding of the true colour of the restoration of the object degree. The higher the colour rendering index, the more real the colour reflection, usually high-quality LED light source colour rendering index up to 85 or more, the definition of daylight and incandescent lamps for 100). The ability of a light source to reveal colour to an object is called colour rendering, and is achieved by comparing the appearance of the colour of an object with a reference or benchmark light source (incandescent or daylight) of the same colour temperature. The spectral content emitted by the light determines the colour of the light from the light source, the

Colour rendering index diagram
6, light decay: LED light failure refers to the LED after a period of time after the light, its light intensity will be lower than the original light intensity, and the low part of the LED light failure. According to international practice, 30% of the light failure can be identified as product failure, many low-quality products less than half a year has exceeded this value, affecting the light failure of a number of factors, the quality of the light source itself, the driver, heat dissipation are important factors affecting the light failure.

Five: factors affecting the quality of LED

1, the advantages and disadvantages of the selected raw materials.

2, whether the encapsulation process is perfect (there is no dust, components fit perfectly), heat dissipation copper pad material.

Six: life: the theoretical life of high-quality LED 100,000 hours!

Why is the service life of LED lamps and lanterns some very short or even less than a year, the relationship between the lamps and lanterns of the life of many factors, such as: the quality of the driver power supply itself, the driver power supply and the matching degree of light source, lamps and lanterns of the assembly process and so on.

Main indicators and parameters of LED selection缩略图

Main indicators and parameters of LED selection

1, brightness
LED light brightness is the most concerned about the topic of the user, brightness can be explained from two aspects.
Brightness L: luminous flux of the luminous body in a specific direction unit stereo angle unit area. Unit: Nitro (cd/㎡).
Luminous flux φ: the sum of the amount of light emitted by the luminous body per second. Unit: lumens (Lm), said the luminous body of how much light, the more luminescence the greater the number of lumens.
Usually LED lights are marked with luminous flux, users can judge the brightness of LED lights according to the luminous flux. The higher the luminous flux, the higher the brightness of the light.
2, wavelength
Wavelength consistent LED, the same colour. There is no LED spectrophotometer producers are difficult to produce products with pure colour.
3, colour temperature
Colour temperature is a unit of measurement to identify the colour of the light, expressed in K value. Yellow light is "3300k below", white light is "5300k above", there is a kind of intermediate colour "3300k-5300k".
4, leakage current
LED is a unidirectional conductive light emitter, if there is a reverse current, it is called leakage, leakage current is large LED, short life.
5, anti-static ability
Antistatic ability of the LED, long life, and therefore high prices. The market market many fake and shoddy products in this one do very bad, this is also expected how many years of life, greatly shortened the root cause.

Main indicators and parameters of LED selection插图

The choice of LED lamps and lanterns includes the appearance, heat dissipation, light distribution, glare, installation and so on. We do not talk about the parameters of the lamps and lanterns today, only about the light source: you really will pick a good LED light source? Light source parameters are: current, power, luminous flux, light decay, light colour, colour rendering. Our focus today is to talk about the last two, first briefly talk about the first four.

  First of all, we often say: "I want how many watts of light", this habit is the continuation of the previous traditional light source, then the light source only a few fixed wattage, basically only in those wattage inside the choice, can not be freely adjusted. And now the LED, drive current slightly change, the power immediately changed! Are you still asking for power? Beware! The same LED light source, with too much current to drive the time, the power is up, but it will cause a decline in luminous efficacy, light attenuation increase. See the chart below:

  In general, redundancy = waste, but for LED operating current, it is saving. In the case of driving current to the rated allowable maximum, reduce the driving current by 1/3, the sacrifice of luminous flux is very limited. Yet the benefits are enormous:

  Light attenuation is greatly slowed;

  Lifetime substantially extended;

  Significant improvement in reliability;

  Higher power utilisation.

  Therefore, a good LED light source, drive current should be used about 70% of the maximum rated current.

  In this case, the designer should directly request the luminous flux, as for what wattage to use, should be decided by the manufacturer itself. This will promote the manufacturers to pursue efficiency and stability, rather than just go to push up the wattage of the light source, at the expense of efficiency and longevity.

  The above mentioned includes these parameters: current, power, luminous flux, light decay. There is a close correlation between them, the use of attention: which is what you really need?

  Light colour

  Traditional light source era, when it comes to colour temperature, we only care about "yellow light, white light", not too concerned about the problem of light colour deviation. Anyway, the traditional light source colour temperature on those kinds of, choose one on the line, generally will not run off where. To the LED era, we found that: LED light colour of any kind. Even with the same batch of lamp beads, there may be deviations to a thousand strange, red, green and green lively ~~~

  They say LED is good, energy saving and environmental protection. But you make it? LED to do a bad business really quite a lot! The following is a large project sent by a V friend of a famous domestic brand of LED lamps and lanterns application scene, look at the people of this light distribution, the colour temperature consistency, the ghost of blue light ……

  In view of this mess, there is a conscientious LED lamps and lanterns factory to the customer commitment: "Our lamps and lanterns, colour temperature deviation ± 150K within! , there are also design companies to do product selection, specifications on the note: "lamp bead colour temperature requirement deviation ± 150K or less".

  The basis of this 150K is cited in the traditional literature concluded that: "the colour temperature deviation ± 150K or less, the human eye is difficult to detect". They think: the provisions of the colour temperature "± 150K or less", you can avoid the occurrence of red and green things. In fact, really "not so simple" ……

Lamp beads, drivers, housing, size, luminous flux, a few metres of illumination, rated power, actual power, power factor, colour rendering index, colour temperature, ambient temperature and light failure.
Main parameters of led lamp beads:
Small power lamp beads: red and yellow: 1.8-2.4V. blue green and white: 3-3.6V. rated current are 20mA.
High-power lamp beads: 1 watt: 3-3.6V, 350 mA.

1, LED with the aspect of very square, can be used in lighting, and indicator, decoration and so on.
2, LED lamp current is DC, LED lamp voltage is not the same, each has its own voltage, such as white light, green light, blue light, are in the 3-3.5V, its normal luminous brightness is 20MM on it, you use 9V voltage plus light up, then, with {(9 - lamp voltage) / 0.02A (mA to A) = to connect the resistor, connected to the 12V is also the same.
3, red light voltage is 1.8-2.1V wavelength 610-620
Green light voltage is 3.0-3.5V wavelength 520-530
Blue light voltage is 3.0-3.5V wavelength 460-470
White light voltage is 3.0-3.5V no wavelength

Although some factories, power plants and other enterprises and institutions have not used LED lights for industrial lighting, but for LED lights, I believe that you will not have heard of the arrival of the LED lighting era, incandescent lamps and energy-saving lamps will be eliminated, which is the inevitable result of technological progress.

  LED lights and traditional lights in the performance is a big difference, especially industrial lighting led lights. So users in the procurement of how to choose a good, suitable for industrial lighting LED lights, the following industrial lighting LED lights on several parameters for a brief introduction.

Main indicators and parameters of LED selection插图2

  1, brightness

  LED lamp brightness is the user's most concerned about the problem, brightness can be explained from two aspects.

  Brightness L: luminous flux of the luminous body in a specific direction unit stereo angle unit area. Unit: Nitrode (cd/㎡).

  Luminous flux φ: the sum of the amount of light emitted by the luminous body per second. Unit: lumens (Lm), said the luminous body of how much light, the more luminescence the greater the number of lumens.

  Usually LED lights are marked with luminous flux, users can judge the brightness of LED lights according to the luminous flux. The higher the luminous flux, the higher the brightness of the light.

  2, wavelength

  Wavelength consistent LED, the same colour. No LED spectrophotometer manufacturers are difficult to produce products with pure colour.

  3、Colour temperature

  Colour temperature is a unit of measurement to identify the colour of the light, expressed in K value. Yellow light is "3300k below", white light is "5300k above", there is a kind of intermediate colour "3300k-5300k". Of course, the user can choose the appropriate colour temperature according to the lighting application environment and operator needs.

  4, leakage current

  LED is a unidirectional conductive light emitter, if there is a reverse current, it is called leakage, leakage current is large LED, short life.

  5, anti-static ability

  Anti-static ability of the LED, long life, and therefore high prices. Many fake and shoddy products on the market do a very bad job on this one, which is expected to be how many years of life, the root cause of the greatly shortened.

  6, life expectancy

  The key to different qualities is the life expectancy, life expectancy is determined by the light decay. Small light decay, long life, the real quality of the LED lights have been done almost no light decay, which is the industry's top level, the industry's vast majority of LED light manufacturers can not reach.

  7, design

  Each product will have a different design, different design for different purposes, the reliability of the LED lamp design aspects include: electrical safety, fire safety, applicable environmental safety, mechanical safety, health safety, safe use of time and other factors.

  8、Protection level

  IP is the abbreviation of Ingress, Protection, IP rating is for the electrical equipment shell of foreign body intrusion protection level, such as: explosion-proof appliances, waterproof and dust-proof appliances, the source of the International Electrotechnical Commission's standard IEC60529.

  The protection level is mostly expressed as IP followed by two numbers, which are used to specify the level of protection. The first number indicates the extent to which the equipment is resistant to fine dust, or the degree to which people are protected from hazards in a sealed environment. This represents the level of protection against the ingress of solid foreign objects, with the highest level being 6. The second number indicates the extent to which the device is waterproof. It represents the level of protection against water ingress, with the highest level being 8.

  Of course, the parameters of LED lights are more than these, such as strobe, heat dissipation, light efficiency, etc. are relevant parameters to judge the quality of LED lights.

  Users should understand that the choice of LED lamps can not be like choosing incandescent lamps only look at the wattage, LED lamp wattage has been unable to accurately interpret the brightness of the LED lamps, high luminous efficacy of the low wattage may also be brighter than the high wattage of the LED lamps. This is the LED era, only with the appropriate parameters to choose a good quality of industrial lighting LED lights. Feel free to ask questions about recolux LED lighting equipment!

Recolux tells you how to design a LED light flashing circuit with a flashing frequency?缩略图

Recolux tells you how to design a LED light flashing circuit with a flashing frequency?

Flashing frequency of 2Hz, that is to say, the LED flashing period of T = 1 / f = 0.5s, that is, 500ms, that is to say, requires the LED light 500ms flashes once, that is, the average second flashes twice. This requirement can be achieved in many ways, the following list of several commonly used examples for your reference and study.

1 The most classic MCU implementation

If we have a processor (such as microcontroller, DSP, ARM, CPLD or FPGA, etc.), it will be very simple to implement the LEDs to blink at a frequency of 2Hz. We only need to use one I/O port of the processor to drive a transistor, which in turn controls the LED's on/off state. By writing a simple programme for the programmer, we can make this I/O port output a high level every 250 milliseconds and then a low level for the next 250 milliseconds. This gives an overall blinking period of 500 milliseconds, which is the 2Hz blinking frequency we are looking for.

The output signal of the I/O port presents a specific waveform: it is actually a square wave signal with a frequency of 2Hz.

Recolux tells you how to design a LED light flashing circuit with a flashing frequency?插图

The following is a common circuit design method of using an NPN-type transistor to control the brightness of an LED. In this circuit, when the I/O outputs a high level, the base of the transistor receives a high level, it will conduct, thus making the LED light; and when the I/O outputs a low level, the base receives a low level, the transistor will cut off, and the LED light then goes out.

Recolux tells you how to design a LED light flashing circuit with a flashing frequency?插图2

2 Use 555 timer is very

Common 555 timer, it is very powerful, it can generate a frequency of up to 300KHZ and adjustable duty cycle PWM wave. For its operation as a square wave generator, the period of the output waveform is calculated by the following formula: TH (high level time) = ln2 × R1 × C1, and TL (low level time) = ln2 × R2 × C1, where ln2 ≥ 0.7. Taking the given resistors R1 and R2 of 768KΩ, and capacitor C1 of 470μF as an example, we can calculate TH and TL as about 250ms each. TL are each about 250 ms. Therefore, the period T of the entire square wave is the sum of TH and TL, which is 500 ms, and the corresponding frequency is 1 divided by the period T, which is 2 Hz.

We know that the output of the 555 timer has a driving capability of about 200mA, so we only need to drive an LED lamp in case we don't need additional components such as transistors to enhance its driving capability. You can directly connect the LED lamp to the output pin (pin 4) of the 555 timer.

Recolux tells you how to design a LED light flashing circuit with a flashing frequency?插图4

3 Multi-Harmonic Oscillator This is a very classic LED alternating blinking circuit, which uses two NPN transistors and capacitor charging and discharging principle to achieve the alternating blinking effect between LED1 and LED2. If you only need to control one or a group of LEDs, you can use a resistor instead of LED2.This circuit is a multi-harmonic oscillator circuit, where one of the transistors is in the on state and the other transistor will cut off, and through the coupling of capacitors and resistors, these two transistors will alternate into the on and cut off state, which will result in a self-excited oscillation. This oscillation mechanism makes the LED1 and LED2 can achieve a smooth alternating flashing effect.

Recolux tells you how to design a LED light flashing circuit with a flashing frequency?插图6

The working principle of this circuit is based on the charging and discharging process of the two NPN transistors and capacitors. At the moment of power-on, due to the small difference between the two sides of the circuit, so the two transistors on time will be first and later, resulting in one of the transistors on first, while the other is in the cut-off state, forming a temporary stable state. Take transistor Q1 on, transistor Q2 cut-off, for example, at this time the collector of Q1 (i.e., the left end of the capacitor C1) voltage is 0, while the base voltage of Q1 is about 0.7 V. At the same time, the capacitor C1 through the resistor R2 for charging, while the capacitor C2 is also charged through the resistor R4. Assuming that the supply voltage VCC is 5V, when capacitor C2 is fully charged, the voltage at both ends of it is 4.3V (0.7V at the left end and 5V at the right end). Since the resistance value of R4 is much smaller than R2, the charging speed of capacitor C2 is much faster than that of C1. When the voltage at the right end of C1 reaches 0.7V, Q2 starts to conduct. At this time, the voltage at the right end of capacitor C2 is directly pulled down to 0V, but because the voltage at the two ends of the capacitor can not be changed abruptly, the voltage at the left end of capacitor C2 instantly becomes -4.3V, resulting in the immediate cut-off of Q1, forming another temporary stable state. Then, capacitor C2 begins to discharge through resistor R3, and after discharging, it begins to reverse charge. When the voltage at the left end of capacitor C2 reaches 0.7V, Q1 conducts again. Similarly, the conduction of Q1 will make the voltage at the left end of capacitor C1 become 0V, which in turn feeds back to the voltage at the right end of capacitor C2 become -4.3V, which makes Q2 cut off, and then enter the next transient steady state. This process will be repeated, so as to achieve the effect of LED1 and LED2 flashing alternately.

The oscillation period T of this polytuned oscillator can be calculated by the formula T=0.7(R2C1+R3C2). Since the values of resistors R2 and R3, capacitors C1 and C2 are the same, the period can be simplified to T=1.4×R2×C1. By adjusting the values of capacitors C1 and C2 as well as resistors R2 and R3, we can change the frequency of the LED's blinking. This circuit may be difficult for beginners to understand, but we can gradually master its working principle through practice.

Summary: This article introduces three commonly used LED blinking programme.

The first programme using the processor to achieve, although the process is relatively simple, but the premise is that the original system has a processor can be used, otherwise in order to a single LED blinking function and the design of a separate processor is uneconomical, high cost.

The second programme uses 555 timer, is a commonly used method, only a 555 chip and some capacitors and resistors to achieve the LED blinking, its principle is simple and low cost.

The third scheme is based on the classic polyharmonic oscillation circuit, only two transistors and a few capacitive resistors can achieve the LED alternately blinking, with a lower cost.

Translated with DeepL.com (free version)

For more LED lighting issues, please feel free to consult recolux

LED controllable constant current source drive system design scheme缩略图

LED controllable constant current source drive system design scheme

LED as the third generation of lighting light source, has the advantages of low operating voltage, low power consumption, high luminous efficiency, long life, etc. LED is a non-linear device, when the LED on, as long as the LED voltage changes slightly, will make the current is too large leading to LED device heat damage. LED's operating characteristics of the quality of the power supply is very dependent on the degree of power supply, so the realization of a high-quality power supply is important to improve the quality of LED lighting, power utilization, extend the service life of LED. Power supply is of great significance to improve the lighting quality of LEDs, power utilization, and extend the service life of LEDs. The stability of the power supply mainly depends on the LED drive circuit design, constant current source drive is the best LED drive mode, the use of constant current source drive, LED current will not be affected by the voltage, ambient temperature changes, as well as the LED parameters of the dispersion, so as to keep the current constant, and give full play to the LED's various excellent characteristics. Currently widely used constant current source has two forms: one is a linear power supply to improve the constant current source, the other is a switching power supply constant current source. Linear power supply to improve the type of constant current source of linear loss, the scope of application is small; switching power supply type constant current source of poor reliability, adapt to the small range, and high cost. Therefore, economical and practical, reliable performance of CNC constant current source has been widely used. In this paper, for the small power LED in the existing lighting system in the drive mode of some of the deficiencies, the design of a highly efficient drive system, proposed a corresponding new type of drive system.

  1 LED characteristics

  1.1 LED volt-ampere characteristics

  The mathematical model of LED volt-ampere characteristics can be expressed as:

LED controllable constant current source drive system design scheme插图

  Where V is the LED starting voltage; RS indicates the slope of the volt-ampere curve; IF indicates the LED forward current; T indicates the ambient temperature; △VF/△T is the temperature coefficient of the LED forward voltage, which has a typical value of -2V/°C for most LEDs. From the mathematical model of the LED, in a certain ambient temperature conditions LED in the forward conduction after the forward voltage of the small changes will cause a large change in the LED current.

 1.2 LED temperature characteristics

  The size of the LED forward current is with the temperature changes, white LED operating current is generally about 200mA, when the ambient temperature once more than 50 ℃, white LED allowable forward current will be reduced and not up to the normal luminous brightness of the required operating current, in this case, if you still apply high current, it is easy to make the white LED aging.

  1.3 LED optical properties

  The luminous flux of the light source refers to the visible light energy passing through the 4π stereo angle per unit time. The relationship between white LED current and luminous flux is shown in Figure 1, with the increase of current, the luminous flux of the LED increases nonlinearly and gradually tends to saturation. The reason is mainly because with the increase in current and time, the internal temperature of the high-power LED rises, which occurs in the P/N junction region of the carrier composite probability decreases, resulting in a reduction in the LED luminous efficiency.

LED controllable constant current source drive system design scheme插图2

  2 system program selection and comparison

  2.1 Core controller selection

  Controller using the more common STC series microcontroller STC89C52, a high-performance 8-bit microprocessor with 8K-byte flash programmable erasable read-only memory (FPEROM-FalshProgrammableandErasableReadOnlyMemory). The device is fabricated using high-density non-volatile memory manufacturing technology and is compatible with the industry-standard MCS-51 instruction set and output pins. With the combination of a versatile 8-bit CPU and flash memory in a single chip, STC's STC89C52 is a highly efficient microcontroller that provides a flexible and inexpensive solution for many embedded control systems.

 2.2 Clock function module selection

  Program 1 uses the DS1302 clock chip. This chip has a small size, few pins, and is very easy to operate. The disadvantage is that the use of external backup battery and external crystal oscillator, the hardware line is more complex, the cost is higher.

  Program 2 uses DS12C887 clock chip. This chip, relatively large size, internal integration of rechargeable lithium batteries, but also integrated 32.768kHz standard crystal, can effectively maintain the continuity of time, very convenient to use, but expensive.

  Scheme 3 uses the timer of the microcontroller (crystal 11.0592M) to design the clock. The time is displayed on the 1602 LCD, and the hours, minutes and seconds of the clock are adjusted with a separate keyboard, and the timer can be set. Low cost, do not need to enable other chips and peripheral circuits in, but the program is more complex.

  Considering the cost-effective and circuit optimization issues, so choose program 3.

2.4 Constant current source module selection

  Scheme 1 uses a microcontroller to generate PWM signals, output to the Darlington tube, through the filter to eliminate ripple, to achieve the function of constant current source. Using PWM pulse to achieve constant current source can simplify the hardware circuit, easy to control and regulate, but the program is difficult to ensure the accuracy, to adapt to the design of the precision requirements of the higher technical difficulty, and the program is difficult to adapt to the application of a large range of current regulation, ripple and stability and other factors, it is difficult to achieve.

  Program 2 by the operational V / I conversion circuit constitutes a constant current circuit. Constant current circuit composed of operational amplifiers to get rid of the transistor constant current circuit is limited by the shortcomings of the process parameters. This scheme can realize 0~5V/0~500mA V/I conversion, and the conversion accuracy is high. If the input is controlled by a microcontroller with a digital potentiometer, a numerical control constant current source can also be easily realized.

LED controllable constant current source drive system design scheme插图4

  Program 3 through the specialized constant current / constant voltage chip LT1769 and a simple control line to achieve voltage-controlled current source program. This constant voltage chip has a high degree of integration, the use of the control system hardware and software have become relatively simple advantages. But the disadvantage is that the program is not flexible enough to achieve; due to the chip precision is not high, the device performance is limited to the performance of this dedicated chip performance indicators allowed. So this design is generally only suitable for precision requirements are not high, but the integration and portability requirements of high occasions, it has been proved that this is not to do the ideal CNC current source to realize the program.

  In view of the arguments and comparisons, the final choice of program 2.

 2.5 D / A converter selection

  For D / A converter, I use a very common 8-bit D / A converter DAC0832, its conversion time of 1 μs, the operating voltage of +5V ~ +15V, the reference voltage of ± 10V, and the microprocessor interface is fully compatible with the low price, simple interface, conversion control is easy, etc., in the application of microcontroller systems are widely used. Its D/A converter consists of 8-bit input latch, 8-bit DAC register, 8-bit D/A conversion circuit and conversion control circuit.

  3 Hardware circuit design

  3.1 System power supply circuit

  The power supply utilizes positive voltage integrated regulator LM7812 and negative voltage integrated regulator LM7912 to provide symmetrical positive/negative 12V regulated output, which is supplied to the op-amp, and then regulated to 5V output by LM7805, which is supplied to the microcontroller.

3.2 LED Driver Circuit

  The circuit can easily realize the voltage/current conversion. Operational amplifier U1A constitutes a comparator, U1C constitutes a voltage follower, playing the role of negative feedback. Input signal Vi compared with the feedback signal Vf, the output voltage V1 at the output of the comparator U1A, V1 control the output voltage V2 of the op-amp U1B, thus changing the output current IL of the transistor Q1, and the output IL affects the feedback voltage Vf, to reach the purpose of tracking the input voltage Vi. The output current IL is calculated as IL=Vf/R13, because the negative feedback makes Vi=Vf, so IL=Vi/R13. If R13 takes the value of 10Ω, the V/I conversion of 0~5V/0~500mA can be realized; if the performance parameters of the selected device are stable, and the amplification of the op-amps UA1 and UA2 is large enough, the conversion accuracy is higher. the voltage of V13 is controlled by the MCU. With the D / A output control, can easily realize the digital constant current source output.

For more LED lighting issues, please feel free to consult recolux for free

Certification and testing standards for LED lighting products exported to Europe and the United States缩略图

Certification and testing standards for LED lighting products exported to Europe and the United States

Nowadays, the lamps exported to Europe and the United States are mainly LED products. When it comes to LED standards, Chinese manufacturers say, Europe and the United States high demand for technical and safety standards are invisible technical barriers to trade. The industry believes that domestic LED lighting practitioners to break these technical barriers to overseas markets, first need to understand the European and American LED standards for LED lighting products, safety, electromagnetic compatibility, performance and other requirements.

Certification and testing standards for LED lighting products exported to Europe and the United States插图

  First, Europe and the United States the main standards bodies and certification mark

UL: UnderwriterLaboratoriesInc. abbreviation, UL safety testing institute is the most authoritative in the United States, but also in the world engaged in safety testing and identification of the larger civil institutions.

FCC:FederalCommunicationsCommission,isanindependentagencyoftheU.S.Government,directlyresponsibletoCongress.TheFCCcoordinatesdomesticandinternationalcommunicationsthroughthecontrolofradio broadcasting,television,telecommunications,satellitesandcable.

ETL: short for ETL ElectricalTestingLaboratories, ETL Laboratories was founded by American inventor Thomas Edison in 1896, and enjoys a high reputation in the United States and around the world. The "us" in the lower right indicates that it applies to the U.S., and the "c" in the lower left indicates that it applies to Canada, while both "us" and "c" are applicable in both countries.

EnergyStar: EnergyStar is a U.S. government-led energy conservation program for consumer electronics products. The EnergyStar program was launched in 1992 by the U.S. Environmental Protection Agency (EPA) to reduce energy consumption and greenhouse gas emissions from power plants.

IEC: International Electrotechnical Commission, is the world's earliest established international electrical standardization body, responsible for electrical engineering and electronic engineering in the field of international standardization work, the world's countries have nearly 100,000 experts in the development of standards to participate in the IEC, the revision of work.

ENEC: EuropeanNormsElectricalCertification, the European standard electrical certification is for specific and in line with European standards for products (such as lighting, components, and office & data equipment) used by the general European standard, ENEC mark is the European safety certification of the general mark, the beginning of the year 2000, the original only allowed European manufacturers to use "ENEC". In 2000, the "ENEC" mark was only allowed to be used by European manufacturers, and it is now open for use by all manufacturers in the world.

Second, LED products exported to the EU market standards

  Exported to the European Union countries need to be certified by including safety certification tests and electromagnetic compatibility certification tests, the main certification labeling CE and ENEC, certification standards mainly include: IEC/EN:60598-1 (general requirements and testing of lamps and lanterns), IEC/EN:60598-2-3 (road and street lighting fixtures and safety requirements), IEC/EN62031 ( LED module general safety requirements), IEC/EN62031 ( LED module general safety requirements), IEC/EN62031 ( LED module general safety requirements), IEC/EN62031 ( LED module general safety requirements), IEC/EN62031 ( LED module general safety requirements). General safety requirements for LED modules) IEC/EN:61000-3-2 (Limits for harmonic current emissions from equipment with single-phase input currents ≤16A),IEC/EN:61000-3-3 (Limits for voltage fluctuations and flicker in low-voltage power supply systems),IEC/EN61547 (Requirements for electromagnetic compatibility immunity of equipment used for general illumination),IEC/EN55015 ( Electrical lighting or type of equipment radio harassment characteristics of the limits and measurement methods).

 Third, LED products exported to the North American market standards

The main certifications for export to the North American market are UL, ETL, FCC and ENERGYSTAR, etc. LED road lighting products UL certification references UL8750 or UL60950, UL1598 two standards, do not test the lamps and lanterns of the EMC characteristics of the ETL certification test references are exactly the same as the UL standard.FCC certification references FCCPart15B, ClassAdigitaldevice. FCC certification references FCCPart15B, ClassAdigitaldevice test limit standards, do not test the safety characteristics of the lamps; ENERGYSTAT (ENERGY STAR) is mainly for residential and commercial lighting class LED lamps and lanterns photoelectricity performance requirements, LED road lighting is not listed.

Certification and testing standards for LED lighting products exported to Europe and the United States插图2

FCC is the U.S. federal law of the radio harassment of teletext products (EMI) characteristics of the limit value of mandatory certification, LED lamps and lanterns of the FCC certification test and the European Union CE in the EMC certification test has a big difference, the main performance as follows:

1, LED lamps and lanterns of the FCC certification only test EMI, does not include EMS test items; CE in the electromagnetic compatibility test are two need certification test;

2, LED lamps and lanterns FCC certification is divided into ClassA and ClassB two categories, the two types of test limits are completely different, CE certification of radio harassment test limit standard only one, limit size and FCC ClassB equivalent;

3, LED lamps and lanterns FCC certification conducted harassment sweep test frequency from 0.15MHz to 30MHz end, CE certification in the conducted harassment sweep test frequency from 9KHz to 30MH end;

4, LED lamps and lanterns FCC certification space radiation harassment sweep test frequency from 30MHz to 1GHz end, CE certification in the space radiation harassment sweep test frequency from 30KHz to 300MH end;

5, FCC certification requirements are more demanding, its EMI certification test limit standards usually require a margin of 6dB or more, CE certification of EMI test margin of 3dB or more can be;

U
  In the UL certification of LED lighting products, drive power certification test can choose UL1310 or UL60950. the main differences between the two standards are as follows:

1, UL1310 is CLASSII (provide limited voltage and capacity of the power supply) power supply equipment safety standards, through the UL1310 certified power supply for the CLASSII power supply, the use of CLASSII power supply to do the cUL (Canadian market) certification of LED lighting fixtures can be exempted from the relevant safety tests; UL60950 is information technology class (referred to as IT) equipment UL60950 is the information technology class (referred to as IT) equipment safety standards, the scope of its applicable certification is greater than UL1310, but the use of UL60950 certified power supply to do cUL (Canadian market certification) LED lighting certification, not exempted from the relevant safety tests;

2, UL1310 standard output voltage under any load conditions in the power supply maximum output voltage (including no load) of the peak exposed contact voltage of 42.4V, when the equipment does not contain can be automatically in the output circuit disconnect device maximum output volt-ampere is not more than 100 volt-ampere; UL60950 is the definition of the output voltage under normal conditions, the voltage between any two touchable circuit parts, or The voltage between any two accessible circuit parts and the protective grounding terminal of Class I equipment does not exceed 42.4V AC peak, or 60V DC value;

3, UL1310 certification applies only to 120 or 240Vac nominal voltage in the grid CLASSII power supply equipment, UL60950 applies to the rated input voltage does not exceed 600Vac information technology products, for the 277V voltage system UL certification of LED lighting products drive power supply, can only refer to the UL60950 standard certification test.

UL certification

UL certification in the United States is a non-compulsory certification, mainly product safety performance testing and certification, the scope of its certification does not include product EMC (electromagnetic compatibility) characteristics. The following is a brief introduction to the LED road lighting products involved in UL8750, UL1310 and UL60950. UL8750 applies to the minimum safety requirements for LED lighting components that will be installed in non-hazardous locations rated at 600V branch circuit or lower, and the same applies to the minimum safety requirements for LED light sources connected to batteries, fuel cells, etc., isolated (no effective connection) power supply. UL1310 applies to CLASS2 power supply equipment that contains an input voltage of 120 or 240 Vac through software or direct plug-in connections to 15 or 20 A AC branch circuits or potentially less than 150 V grounded, that uses an insulated transformer and that can be incorporated into rectifiers and other components to provide DC or AC electrical energy, and that is intended to be used to provide energy for low-voltage electrical operations; UL60950 applies to safety standards for information technology (IT) equipment, including cell phones, computers and their peripherals, such as projectors, printers, etc., but also includes the output of the power supply can be taken with the LPS (restricted power supply) safety circuit;

In the UL certification of LED lighting products, drive power certification test can be used UL1310 or UL60950. the main differences between the two standards are as follows:

1, UL1310 is CLASSII (provide limited voltage and capacity of the power supply) power supply equipment safety standards, through the UL1310 certified power supply for the CLASSII power supply, the use of CLASSII power supply to do cUL (Canadian market) LED lighting fixtures certification, exemption from the relevant safety tests; UL60950 is information technology class (referred to as IT) equipment UL60950 is the information technology class (referred to as IT) equipment safety standards, the scope of its applicable certification is greater than UL1310, but the use of UL60950 certified power supply to do cUL (Canadian market certification) LED lighting certification, not exempted from the relevant safety tests;

2, UL1310 standard output voltage under any load conditions in the power supply maximum output voltage (including no load) of the peak exposed contact voltage of 42.4V, when the equipment does not contain can be automatically in the output circuit disconnect device maximum output volt-ampere is not more than 100 volt-ampere; UL60950 is the definition of the output voltage under normal conditions, the voltage between any two touchable circuit parts, or The voltage between any two accessible circuit parts and the protective grounding terminal of Class I equipment does not exceed 42.4V AC peak, or 60V DC value;

3, UL1310 certification applies only to 120 or 240Vac nominal voltage in the grid CLASSII power supply equipment, UL60950 applies to the rated input voltage does not exceed 600Vac information technology products, for the 277V voltage system UL certification of LED lighting products drive power supply, can only be cited as the UL60950 standard certification test.

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