What issues need to be considered when designing LED driver circuits?

LED has many advantages such as environmental protection, long life, high photoelectric efficiency, etc. In recent years, the application in various industries has been developed rapidly, and the driving circuit of LED has become a key factor in product application. In theory, the service life of the LED is more than 100,000 hours, but in the actual application process, due to the improper design of the drive circuit design and drive mode, the LED is extremely vulnerable to damage.

When designing an LED drive circuit, you need to know the LED current and voltage characteristics. Due to different LED manufacturers and LED specifications, current and voltage characteristics are different. Now taking the typical specifications of white LED as an example, according to the LED current and voltage changes, the general application of forward voltage is about 3.0-3.6V, the typical value is 3.3V, the current is 20mA, when the forward voltage across the LED exceeds 3.6 After V, the forward voltage has only a small increase, but its forward current may multiply and increase the temperature of the LED luminous body too quickly, thereby accelerating the LED light attenuation, shortening the life of the LED, and even burning in severe cases. Bad LED. According to the change characteristics of the voltage and current of the LED, strict requirements are imposed on the design of the driving circuit.

At present, many manufacturers of LED light products (such as guardrails, lamp cups, and projection lights) use resistance-capacitance buck, and then add a voltage stabilizing diode to supply power to the LED. This way is simple and cheap to drive the LED, but there are very many The big defect is the low efficiency first. It consumes a lot of power on the buck resistor, and may even exceed the power consumed by the LED, and cannot provide a large current drive. Because the larger the current, the larger the buck capacitor is required, so the consumption is decreasing. The greater the energy on the piezoresistor. Secondly, the ability to stabilize the voltage is extremely poor, and it cannot be guaranteed that the current through the LED will not exceed its normal working requirements. When designing the product, the voltage across the LED will be reduced to drive the power, which is at the cost of reducing the brightness of the LED. The LED brightness is not stable when the resistance-capacitance buck is used to drive the LED. When the power supply voltage decreases, the LED brightness becomes darker. When the power supply voltage increases, the LED brightness becomes brighter.

According to the characteristics of LED current and voltage changes, it is feasible to use constant voltage to drive LEDs. Although commonly used voltage stabilizing circuits have the disadvantages of insufficient voltage stabilizing accuracy and poor current stabilizing ability, they may be over-precisely designed in the application of certain products. , Its advantages are still irreplaceable by other driving methods.

The constant current drive mode is an ideal LED drive mode. It can avoid the current fluctuation caused by the change of the LED forward voltage, and the constant current makes the brightness of the LED stable. Therefore, many manufacturers use constant current to drive LEDs. Another LED driving method is feasible, which is neither constant voltage nor constant current, but through the design of the circuit, when the LED forward voltage increases, the drive current is reduced, ensuring the safety of LED products. Of course, the increase of the forward voltage can only be within the range of the LED, too high will damage the LED.

The ideal LED driving method is to use constant voltage and constant current, and cascade multiple LEDs in series. But the cost of the drive increases. In fact, each driving method has advantages and disadvantages. According to the requirements of LED products and application occasions, it is reasonable to choose the LED driving method and accurately design the driving power supply.

 

If you want to know more, our website has product specifications for LED driver, you can go to ALLICDATA ELECTRONICS LIMITED to get more information

What is the development status and trend of led display?

 Over the past few years, with the further release of the market, the entire LED display industry has regained its vitality, and market competition has intensified. However, in contrast, more and more companies have entered the LED display industry. With this overall increase in competition, it is even more difficult to occupy a position in the LED display industry and become a leader.

In recent years, the steps of industrial transformation and upgrading have been accelerated, but the threshold for entering the LED display industry has not been raised year-on-year, which has also caused the current industrial situation: on the one hand, there are an increasing number of small and medium-sized screen companies with mixed fish and dragons; On the one hand, the threshold for creating a well-known brand in the industry is getting higher and higher; it is well known that the LED display industry has not born a well-known brand with a non-industry background for a long time.

　　 This situation has also caused multi-LED display practitioners to fall into a development puzzle: in the end, the market is getting better and better, will it cause many industry recruits and veterans to re-enter this industry? Or is it that the market is getting harder and harder, so it hasn't been a long time since a new brand from 0 to 1 has risen?

LED display development trend

　  1. Development towards energy saving trend

　  Energy saving and environmental protection has always been a new proposition for future life. The LED display itself is very energy-saving. Its characteristics are: high light efficiency, long life, easy control, and maintenance-free. It is a new generation of solid cold light source, with soft light, gorgeous, colorful, low loss, low energy consumption, and is a green and environmentally friendly product. But the power consumption is not small when made into LED display screen. Large LED screens are all large screens and require many points to form. Reducing the power consumption of LED display screens and realizing real energy saving must be an important development trend of LED display.

　　2. Development towards light and thin trend

      At present, almost everyone in the industry advertises that their boxes are light and thin. Indeed, thin and light boxes are an inevitable trend to replace iron boxes. In the past, the weight of the iron box itself is not low, and the weight of the steel structure makes the whole very heavy. In this way, many floors of the building are difficult to withstand such heavy attachments. The load-bearing balance of the building and the pressure of the foundation are not acceptable, and it is not easy to disassemble and transport. The cost is greatly increased, so the thin and light box is not allowed by all manufacturers. A trend that does not update.

　 3. Towards the trend of patent protection

    The LED industry is fiercely competitive, and almost every company is competing for the market, grabbing customers, and expanding its scale, but few companies really focus on product research and development. In fact, in order to maintain technological competitiveness and reduce the risk of technology spillovers, patents are good. Way of protection. As the industry slowly matures, regulates, and protects its intellectual property rights and intangible assets through patent applications, it is also an inevitable development trend for the LED large-screen industry.

4. To the trend of rapid and accurate splicing

　　This is mainly for LED rental display. The characteristic of leasing is that it is often disassembled and assembled to meet temporary needs, so the display boxes must be able to be spliced quickly and accurately. Hanchuang LED rental screen is super light and thin. Light and thin design is the demand of LED rental screens. LED display screens require frequent disassembly and handling because of the particularity of their application places. The thinner and lighter the LED rental screen is, the more convenient the transportation is, and it can also save more costs. Therefore, rapid and accurate installation is also bound to be the development trend of LED display screens.

　　 5. Towards the trend of standardization

　　 LED display screens have sprung up like mushrooms, but only a few can be recognized by the industry. Since many small enterprises were established, because of their small size, small capital, and incapable of keeping up with their R&D capabilities, they tried to take shortcuts, sloppy design, and even plagiarized designs from large companies. The customer has a headache, and this behavior is extremely irresponsible to the customer. Therefore, the standardization of LED large-screen products is also an inevitable trend.

　　 6. The trend towards smaller pitches

 Small pitch has always been one of the products of the heat. At present, the indoor small pitch has broken through a few points, and the outdoor small pitch has also broken below P2. With the development of technology, the pitch will become smaller and smaller.

 

If you want to know more, our website has product specifications for led display, you can go to ALLICDATA ELECTRONICS LIMITED to get more information

What is the principle of LED lighting technology?

 Semiconductor lighting is a brand-new lighting that is revolutionary and updated. Compared with the previous traditional lighting, it has many advantages, of course, there are also deficiencies. Historical and dialectical views should be used to analyze the analysis vertically and horizontally, which will help to better understand LEDs and allow LED lighting to develop better.

Semiconductor lighting can be divided into LED lighting, OLED lighting and LED laser lighting. At present, the absolute dominant position is blue chip white LED lighting, OLED lighting has also appeared in many exhibitions, and LED laser lighting has begun to show its technical advantages in automotive lighting. This mainly involves LED lighting technology and related content.

Principles and characteristics of LED lighting technology

As the third milestone of lighting and the fourth-generation light source, the blue chip white LED has the principle of majority carrier "hole" in P-type semiconductor and majority electron "electron" in N-type semiconductor. Under the action of the applied electric field, the electron crosses the PN junction barrier between the two and enters the PN junction region and the other region. In this process, the "hole" and "electron" recombine, releasing energy to emit blue light, and the blue light is emitted by the encapsulation layer and emits light The powder absorbs and the phosphor converts to emit red-green light. The red-green light and the blue light transmitted from the phosphor encapsulation layer form the red, green, and blue primary colors. The light is mixed into white light at various points in the space.

The LED light source is a solid-state semiconductor electronic luminescence, which belongs to a special non-linear positive resistance, which makes it can light up and work normally without a current stabilizer etc. below the rated operating point. However, when it is overloaded above the rated operating point, the positive resistance becomes smaller and smaller, and tends to 0 resistance. Its voltage and current relationship changes dramatically, resulting in small power supply voltage fluctuations, which will greatly increase the current, so it needs to be commonly known as Drive power to limit and stabilize the operating current. Light efficiency is one of the most important indicators of LED. The light efficiency is from the first few Lm/W in the 1990s to 303 Lm/W in 2015, and its electro-optical conversion efficiency has reached as high as 44.5%, which means 44.5% of electric energy It can be converted into visible light energy, which is 30 times that of conventional incandescent lamps, 4.5 times that of ordinary fluorescent lamps, and about 3 times that of high-end rare earth fluorescent lamps, high-pressure sodium lamps and metal halide lamps.

In addition, because LEDs are electronic devices, their normal service life is very long. Generally, the life of high-power LEDs is 50,000 hours, and the life of low-power LEDs is even as long as 80,000 to 100,000 hours. The low LED voltage makes it easy to combine, and can be completely integrated with the electronic drive circuit and control circuit. Compared with the control device of the traditional gas discharge light source, its principle makes the drive circuit structure greatly optimized, and the reliability and life are greatly improved. The control circuit and intelligence are extremely convenient, which truly opens a new era of revolutionary lighting and intelligent lighting.

Without LED, there can be no real development of intelligent lighting and visible light communication. In addition, although there is a blue peak in the spectrum of the LED, it covers the entire visible spectrum, and it is much more continuous and smooth than the spectrum of the three primary color fluorescent lamps and energy-saving lamps in traditional lighting. However, low LED voltage is both an advantage and a disadvantage.

First of all, the low voltage can be combined into a variety of voltage and current application forms, resulting in a wide variety of terminal product specifications, resulting in increased difficulty in large-scale production, increased production costs, and at the same time makes standardization and standardization difficult.

Second, mainstream LEDs have inherent defects of uneven spatial distribution of luminosity and chromaticity, making it more difficult to improve light quality.

Third, the advantages of LEDs with small light-emitting points and high brightness for display technology have become more prominent shortcomings in lighting, glare, glare and even photobiological safety.

 

If you want to know more, our website has product specifications for LED lighting technology, you can go to ALLICDATA ELECTRONICS LIMITED to get more information

What are the core indicators and parameters of rechargeable batteries?

 Rechargeable batteries are rechargeable batteries with a limited number of recharges and are used with chargers. No. 5 and No. 7 are generally sold in the market, but there is also No. 1. The advantages of rechargeable batteries are economic, environmental protection, sufficient power, suitable for high-power, long-term use of electrical appliances (such as Walkman, electric toys, etc.). The voltage of the rechargeable battery is lower than that of the same type of disposable battery. The AA battery (Charge 5) is 1.2 volts, and the 9V rechargeable battery is actually 8.4 volts. Now the general charging times can be around 1000 times.

Core indicators of rechargeable batteries

1. Safety performance

Batteries with unsatisfactory safety performance indexes are impossible to accept. Among them, the biggest impact is explosion and liquid leakage. The occurrence of explosion and liquid leakage is mainly related to the internal pressure, structure and process design of the battery (such as failure of safety valve, no protection circuit for lithium ion battery, etc.) and improper operation that is prohibited (such as putting the battery into fire).

2. Capacity

Refers to the total amount of electricity that the battery can discharge under certain discharge conditions. According to the IEC standard and the national standard, the nickel-cadmium and nickel-metal hydride batteries are charged at 0.1C for 16 hours and discharged at 0.2C to 1.0V at 20 ± 50C for the rated capacity of the battery, expressed in C; lithium ion The battery is charged at room temperature, constant current (1C), and constant voltage (4.2V) for 3 hours, and then discharged at 0.2C to 2.75V as the rated capacity of the battery. The unit of battery capacity is mah and Ah (1Ah = 1000mAh).

Take AA2300mAh Ni-MH rechargeable battery as an example, which means that the battery is charged at 230mA (0.1C) for 16 hours and then charged at 460mA (0.2C)

When discharged to 1.0V, the total discharge time is 5 hours, and the discharged electricity is 2300mAah. Correspondingly, if the current is discharged at 230 mA, the discharge time is about 10 hours.

3. internal resistance

The internal resistance of the battery refers to the resistance to the current when it flows through the battery. The internal resistance of the rechargeable battery is very small, and it requires a special instrument to measure more accurate results. The internal resistance of the battery is generally known as the internal resistance of the charged state, even when the battery is fully charged (corresponding to the internal resistance of the discharge state, which refers to the internal resistance of the battery after fully discharged. The internal resistance in the charged state is large and not very stable). The greater the internal resistance of the battery, the more energy the battery consumes itself, and the lower the efficiency of the battery. A battery with a large internal resistance heats up greatly during charging, causing the temperature of the battery to rise sharply. The impact on the battery and charger are great. As the number of times the battery is used increases, the internal resistance of the battery will increase to varying degrees due to the consumption of the electrolyte and the decrease in the activity of the chemical substances inside the battery. The lower the quality of the battery rises faster.

4. Cycle life

Cycle life is the number of repeated charging and discharging that the battery can undergo. The battery life and capacity are in an inverse relationship. The cycle life of a general nickel-metal hydride battery can reach more than 500 times. The life of high-capacity batteries is shorter, but it can also reach more than 200 times. The cycle life is also closely related to the charging and discharging conditions. Generally, the larger the charging current (the faster the charging speed), the shorter the cycle life.

5. Charge retention ability

Charge retention capacity, usually referred to as self-discharge, refers to the retention capacity of the battery in a certain environmental condition under the open circuit state. Self-discharge is mainly determined by many factors such as battery material, manufacturing process, storage conditions and so on. Generally, the higher the temperature, the greater the self-discharge rate. A certain degree of self-discharge of rechargeable batteries is normal. Taking nickel-metal hydride battery as an example, the IEC standard stipulates that after the battery is fully charged, it should be left open for 28 days at a temperature of 20 ± 5 ° C and a humidity of 65 ± 20%. Greater than 60%). The self-discharge of lithium-ion batteries and dry batteries is much smaller.

Rechargeable battery parameters

1. Energy density

The electric energy capacity contained in unit volume or unit weight, for the same power requirements, batteries with high energy density can be smaller in size and lighter in weight.

2, C current

Refers to the amount of current that a fully charged battery is discharged or an exhausted battery is fully charged within an hour. In fact, it is the numerical value of the ampere-hour capacity. For 1800mA. Capacity batteries, the C current is 1800mA. For a 2000mA. Capacity battery, the C current is 2000mA.

3. Open circuit voltage

Refers to the potential difference between the two terminals of the battery.

4. Memory effect

The new battery has fine grains of electrode material, which can obtain the largest electrode surface area. Due to use, the contents of the battery are crystallized. After the crystallization is formed, the crystal grains increase, also known as (passivation), which reduces the available electrode area, and the grown crystal grains will cause an increase in self-discharge and make the battery Reduced capacity and impaired performance. This is the memory effect. The reason for the memory effect is due to incomplete partial charging and discharging of the battery.

5. Self-discharge rate

The charged battery will gradually lose its power even when it is not in use. Generally, the higher the temperature, the more significant the self-discharge.

 

If you want to know more, our website has product specifications for batteries, you can go to ALLICDATA ELECTRONICS LIMITED to get more information

What are the advantages of OLED?

 Unlike LCD, it does not require a backlight module, so its body can be made very slim and long, and it also breaks through the angle limitation of the screen, so more and more mobile devices are now using OLED panels.

And in terms of color performance, viewing angle, refresh rate, response speed, etc., it also loses LCD, which is the future development direction of display devices.

ULED, QLED, SLED, GLED

ULED was launched by Hisense. Its feature is that it realizes partitioned light control, divides the backlight into multiple independent control units, and then precisely controls each unit according to the characteristics of the picture.

As of now, in addition to Hisense, other TV brand companies have launched TVs of this design.

ULED is based on the partitioned light control, plus a series of other image enhancement and optimization technologies. Not only can the screen brightness, color and other parameters be optimized, but also the backlight scanning technology, as well as the success of the picture tailing and jitter.

The addition of zoned light control technology allows the TV to achieve a good contrast between light and dark, so it performs well in HDR.

The full name of QLED is QD-LCD. On the basis of the backlight of the LCD TV, a layer of quantum dot film is added, and quantum dot technology is used to replace the yellow phosphor in the blue LED optical packaging material, so that the picture is displayed. The color reproduction, color gamut, and viewing angle have made significant progress, and we can get a glimpse of the price of the QD-LCD TV on the e-commerce platform.

As for the SLED joint between Konka and LG Display, which means Slim (slim) and Swinging (dazzling), it means that the screen can be ultra-thin while still providing colorful display effects.

The last GLED screen was developed by Skyworth, using WRGB (white, red, green, blue) 4 colors 4K + technology, plus Skyworth's own image processing engine, to optimize the picture effect and improve the picture quality.

The future shows the direction of development

In addition to these seemingly different ED brothers, QD-OLED and Micro-LED are truly future-oriented display technologies.

This QD-LED is also different from QLED, the same is that Samsung mainly promotes and uses QD quantum dot technology.

But the difference is that the former is just an improvement of the LCD panel that uses photoluminescence, and also requires a backlight layer, while the real quantum layer can be electroluminescent, similar to OLED panels, but only the light-emitting diodes in Quantum dot material.

 

As for Micro-LED, countless very tiny LED lights are integrated into semiconductor chips through semiconductor technology, so that each micrometer-level Micro-LED light acts as a pixel, and they can be flexibly controlled to light up.

Such a screen will have excellent performance in terms of power consumption, brightness, delay, and color purity. Obviously, it is a leap forward for the two mainstream display technologies.

 

After reading the above introduction to the common display technology terms on the market, the "variety" of screen names we see in shopping malls is largely just a means used by TV manufacturers for better marketing promotion Don't panic.

However, it should be understood that they are all innovated on the basis of the original LCD or OLED screen technology, and the resulting display effect is also very good.

However, when buying a TV, in addition to considering the screen imaging effect, there are various factors such as size, energy consumption label, price and so on.

 

If you want to know more, our website has product specifications for OLED, you can go to ALLICDATA ELECTRONICS LIMITED to get more information

Analyze DDR2 memory power circuit

The current required for DDR2 and DDR3 memory is large, so most motherboards use switching power step-down mode (PWM).

Memory-powered switching power circuits are generally composed of pulse modulators (PWM), MOS transistors, inductors, and electrical memory, as shown in figure 1.

 

       Figure 1 physical diagram of the on-off power supply powered by memory.

The PWM circuit works as shown in figure 2. The PWM chip adjusts the output voltage by controlling the high-speed on and off of the upper and lower tubes. When the upper tube is turned on, the VIN charges the energy storage circuit of the inductor and capacitor through the upper tube and supplies power to the later stage. When the capacitor and inductor is full of electricity, the PWM chip controls and closes the upper tube, and opens the lower tube so that the energy storage circuit composed of inductor and capacitor can form a closed loop, so that the inductor and capacitor discharge continue to supply power to the later stage (the lower tube constitutes the discharge loop). In fig. 2, T1 is on and T2 is off. It can be seen from the diagram that the output voltage can be effectively controlled by controlling the duty cycle of T1.

Fig.2 The PWM circuit works.

Intel H61 single-bridge chip board works.

     The Intel H61 chipset is an upgrade of the H55 chipset, supporting the 1155-pin second-generation CPU. of 13, 15, and 17 The function of H61 chipset motherboard is greatly improved, and the ERP energy-saving circuit is set on the standby circuit of the motherboard, which greatly reduces the power consumption of the motherboard when it is on standby. The main difference between the H6I chipset and the normal motherboard after using the ERP energy-saving circuit is that there is no standby power supply before the motherboard does not press the switch. The Intel H6I chipset motherboard boot circuit works as shown in figure 1.

      Figure 1 operating principle block diagram of the motherboard boot circuit of the Intel H61 chipset.

The Intel H61 chipset motherboard boot circuit works as follows.

The first stage: the main board installed the battery BATI through R299 sent to the DI0 Schottky transistor positive pole, from the negative output RTCVCC for the bridge real-time clock circuit power, RTCVCC after R411 and C465 capacitor delay to get RTCRST# high-level reset South Bridge chip RTC circuit.

The second stage: plug in ATX power supply and connect 220V AC market power, ATX power output ATX_5VSB, through voltage regulator step down to SB_3VSB power supply to IT8728F, used for IT8728F chip trigger module and ERP module power supply.

The third stage: the short switch generates the PANSHW# trigger signal to the 75 pins of the IT8728F, outputs the SLP_SUS_L signal after the internal logic circuit conversion, controls the ERP energy-saving circuit to step down to get the standby power supply of the 3VSB to the bridge and the IT8728F. IT8728F gets standby power supply after internal delay from 85-pin output RSMRST# high-level signal to the bridge, notifying the main board of the bridge standby power supply is normal.          At the same time, the RSMRST# signal is pulled to the high level of the DPWROK through the resistor, and the transmission to the bridge indicates that the power supply is normal. The IT8728F internal delay then sends out the PWRON# of the 3.3V-0V-3.3V jump from the 72 feet to the bridge request to power on. The bridge sends a 3.3V continuous high-level SLP_S3# to the 71 pins of the IT8728F when standby conditions are normal and itself is normal, indicating that power is allowed. Finally, 1T8728F sends out a continuous low-level PSON# signal from 76 pins to pull down the green line of ATX power supply, so that the output of ATX power supply is + 12V, + 5V, + 3.3V to complete the power-up.

       This article is from Allicdata Electronics Limited.