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LED Driver Basics and Its Circuit Design

Author: Apogeeweb
Date: 9 Apr 2018
 34314
LED Driver circuit

Warm hints: The word in this article is about 3800 words and the reading time is about 23 minutes.

Introduction

LED is recognized as the fourth generation of the green light source. It is a solid cold light source. It has many advantages, like high efficiency, long life, safe and environmental protection, small size, high reliability, fast response speed and so on. At present, the same lighting effect is achieved. The power consumption of LED is about 1/10 of incandescent lamps and 1/2 of fluorescent lamps. Many countries and regions have introduced a variety of policies to support the development of the LED industry, so that the industry has become an important part of the country's important industries, giving birth to huge business opportunities. LED driver circuit is very important for LED and LED dimming control can save energy. The driving and dimming of high brightness white LED are hot topics in recent years.

LED driver

Catalog

I LED Driver Basics

1.1 What is a LED Driver

1.2 Characteristics of LED Driver Power Supply

II Types of LED driver

2.1 LED Driver Constant Current

2.2 LED Driver Constant Voltage

III The Application of LED Driver

IV LED Driver Common Use Product Example Diagram

V Led Driver Circuit Basics

5.1 What is LED Driver Circuit

5.2 Types of LED Driver Circuit and Its Classification

VI Novel Driver Circuit Design

VII Basic Suggestion for Designing LED Driver

7.1 LED Current Size

7.2 Chip Fever

7.3 Power Tube Fever

7.4 Frequency Reduction of Working Frequency

7.5 The Selection of Inductors or Transformers

VIII Conclusion


I LED Driver Basics

1. 1 What is a LED Driver

Led driver changes the power supply to a specific voltage current to drive the LED voltage converter. In general, the input of the LED driver includes the high voltage power frequency AC (i.e., the city electricity), the low voltage DC, the high voltage DC, the low voltage and high-frequency AC (such as the output of the electronic transformer). The output of LED driver power is mostly a constant current source that can change voltage with the change of LED forward voltage drop. The core components of the LED power supply include switch controller, inductor, switch component (MOSFET), feedback resistor, input filter device, output filter and so on. According to the requirements of different occasions, there must be input over-voltage protection circuit, input under-voltage protection circuit, LED open circuit protection, over-current protection circuit and so on.

1.2 Characteristics of LED Driver Power Supply

  • > (1) high reliability

Especially the driving power of the LED street lamp is installed at a high altitude, so the maintenance is not convenient, and the cost of maintenance is also large.

  • > (2) high efficiency

LED is an energy-saving product, and the efficiency of driving power is high. It is very important for the power to be installed in the luminaire. The power supply's efficiency is high, but the power consumption is small, and the heat in the luminaire is small, so the temperature rise of the lamp is also reduced. As a result, delaying LED attenuation is advantageous.

  • > (3) high power factors

The power factor is the power grid's demand for the load. In general, there are no mandatory indicators for electrical appliances with a power rating of fewer than 70 watts. Although the power factor of a single electric appliance is low, it has little influence on the power grid; however, in the evening, the power grid will be seriously polluted by a large amount of lighting and the concentration of the same kind of load. There may be some index requirements for power factors for the 30 watts-40 watts LED driver in the near future.

  • > (4) driving mode

Now there are two kinds of traffic: one is a constant voltage source for multiple constant current sources, and each constant current source is supplied to each LED individually. In this way, the combination is flexible, and all the LED failures do not affect the work of other LEDs, but the cost will be slightly higher. The other is the direct constant current power supply, that is, the drive mode of "Keke Hui Bao", which is driven by LED in series or parallel operation. It has the advantage of low cost but poor flexibility, and it also does not affect other LED operation problems when solving an LED failure. The two forms coexist in a period of time. The way of multi-way constant current output power will be better in terms of cost and performance. Maybe it's the main direction in the future.

  • > (5) surge protection

The ability of LED to resist surge is relatively poor, especially the ability to resist reverse voltage. It is also important to strengthen the protection in this area. Some LED lights are outdoors, such as LED street lights. Because of the load shedding and lightning induction, all kinds of surges will be invaded from the power grid, and some surges will cause LED damage. Therefore, the analysis of the driving power of "Zhongke Hui Bao" should be deficient in surge protection. As for the frequent replacement of power and lamps, the LED driver should have the ability to suppress the surge and protect the LED from being damaged.

  • > (6) protection function

To meet the requirements of safety and electromagnetic compatibility, it is best to increase the LED temperature negative feedback in the constant current output, in addition to the conventional protection.

15w LED driver

II Types of LED Driver

2.1 LED Driver Constant Current

According to the driving mode, the common market-led lamp driver is divided into two kinds. One is constant current drive. The characteristic of a constant current drive is that the output current is constant. The output voltage is changed in one range. So we often see that the driving shell is marked out (output: DC**V - **V * * * mA+-5%) in the market. This means that the output voltage is in one of the output voltages. The range, the current is how many ma.

  • A. The output current of the constant current drive circuit is constant, but the output DC voltage varies in a certain range with the different sizes of the load. The load resistance is small, the output voltage is low, the greater the load resistance is, the higher the output voltage is.

  • B. Constant current circuit is not afraid of load short circuits, but it is strictly forbidden to load fully open.

  • C. The constant current drive circuit is ideal for driving LED, but relatively speaking, the price is higher.

  • D. Attention should be paid to the maximum withstand current and voltage used, which limits the number of LEDs used.

2.2 LED Driver Constant Voltage

And the other is the constant voltage drive. The constant voltage driving characteristic is that the output voltage is fixed, and the current is limited to the maximum value with the change of the lamps and lanterns. In this case, the shell usually indicates (output: DC**V **A) the voltage of the output fixed volt, and how many maximum output currents are available. The most common output voltages in the led market are 5V, 12V, 24V, and so on.

  • A. When the parameters in the voltage stabilizing circuit are determined, the output voltage is fixed, whereas the output current varies with the increase or decrease of the load.

  • B. The voltage stabilizing circuit is not afraid of load opening, but load short circuits are strictly forbidden.

  • C.  A regulated drive circuit powers the LED. Each string requires a proper resistor to average the brightness of each string LED.

  • D. The rectified voltage changes will affect the brightness.

III The Application of LED Driver

The application of LED drivers is determined by the LED parameters that we wish to drive. The input voltage and current are the two most important parameters. The propagation lamp comes with a separate explanation on how to calculate the input voltage and current of the LED lamp. This is only a description of the LED lamp's input. People will be able to see the original driving parameters (be sure to identify some driving false targets!!!).

 

We select the corresponding LED driver based on the lamp board's input voltage and current. For example, if the lamp board's input voltage is 37-40V and the input current is 300mA, the LED driver output voltage can be selected to include it, and the current is nearly the same. The formula surface, as well as the voltage greater or lesser than all, must be included. Otherwise, there will be flickering. Low current is acceptable.

LED Driver

Finally, we only need to press the positive and negative pole marked by the lamp plate to weld the drive or connection line. It is necessary to note that the conventional LED-driven output line, the red is the positive pole. The black is the negative pole... If it is a gray line, then the gray is the positive pole, the white is negative... Blue brown line, the blue line is the negative pole, the blue line is the negative pole and so on...

IV LED Driver Common Use Product Example Diagram

LED Driver Common Use Product Example Diagram

Figure 1. LED Driver Common Use Product Example Diagram

Let's see a video about how to make an LED driver:

How to Make a LED driver

V Led Driver Circuit Basics

5.1 What is LED Driver Circuit

An LED driver is an electrical device that regulates the power of an LED or a string (or strings) of LEDs. An LED driver responds to the changing needs of the LED, or LED circuit, by providing a constant quantity of power to the LED as its electrical properties change with temperature.

5.2 Types of LED Driver Circuit and Its Classification

  • A. Charge Pump Circuit

The charge pump circuit is also a DC/DC converter circuit. The charge pump circuit uses the accumulation effect of the capacitor on the charge to store electrical energy. It uses the capacitor as an energy coupling element and controls the power electronic device to perform high-frequency switching, allowing the capacitor to store energy during a part of a period, and the capacitor releases energy during the remaining time. This kind of circuit obtains different output voltages through different connection modes when the capacitor is charged and discharged, and the whole circuit does not need any inductance.

 

The charge pump circuit is relatively small, with fewer components, and lower cost. However, it uses relatively many switching elements. Under the condition of a certain input voltage, the range of output voltage change is relatively small. The output voltage is mostly 1/3~3 times the input voltage, and the circuit power is small, and the efficiency will vary with the output. The relationship between the voltage and the input voltage changes. When there are multiple LEDs, they must be driven in parallel. To prevent uneven current distribution in the branch, a ballast resistor must be used, which will greatly reduce the efficiency of the system.

  • B. Switch Power Circuit

The switching power supply circuit is a DC/DC transform circuit which changes the output voltage by changing the time ratio between switching and turn off. From the circuit point of view, compared with the charge pump circuit, it contains magnetic components, that is inductor or high-frequency transformer. The switching power supply is divided into two types of DC/DC converters, namely, input and output without isolation, namely, "direct connection" and "input and output".

 

The typical circuits of "straight-through" DC/DC converter include Buck, Boost, Buck-Boost and Cuk.

 

The typical circuits of isolated DC/DC converters with input and output are single-ended forward, single-ended flyback, push-pull, half-bridge and full-bridge. The switching power supply circuit can achieve a wide range of voltage output, and the output voltage is adjustable continuously, the output power is large, so the application range is wider, especially in the medium and large power situations.

  • C. Linear Circuit

The linear control circuit regards the semiconductor power device working in the linear region as a dynamic resistor and realizes constant current drive through its control level control. The disadvantage of the linear control circuit is low efficiency, but it has a fast response to the input voltage and load change. The circuit is relatively simple. It is easy to control the current of LED directly, and it is easy to control the high precision of the current.

VI Novel Driver Circuit Design

The actual feedback control of the switching power supply is the output voltage, and the output current control is not easy to be accurate, and the LED lamp is easily damaged when the control of the switching power supply is biased; the efficiency of the linear circuit is not high.

 

Based on the above reasons, a novel LED drive circuit is designed. The circuit uses a single-end flyback switching power supply as the front stage control, and the linear pressure control constant current source is used as the post level control. After converting the single-ended flyback power supply, the DC voltage output can be obtained, which is used as the input of the post-stage voltage-controlled constant current source. Because the input voltage of the constant current source is controlled by a high-efficiency single flyback switching power supply, the pressure control constant current source can accurately control the LED and can change the input voltage of the constant current source in a large range, so the efficiency and precision are guaranteed, and the power supply can be supplied by the city. At the same time, the two-level control is not easy to damage the LED lamp.

Novel High Power LED Lamp Driving Circuit

Figure 2. Novel Driver Circuit Design

The system circuit is shown in Figure 2. The transformer T1, the switch tube Q1, the diode D1 and the capacitor C1 constitute the single end flyback switching power supply, and the operational amplifiers U1, U2 and power transistor Q2 constitute the pressure controlled constant current source, and the MCU STC89C51 is the core control device.

 

When the gray value changes, the microcontroller generates a corresponding brightness control voltage based on the gray value obtained. The brightness control voltage is added to the same phase input of U1. The reverse input terminal of U1 is the LED current signal obtained by U2, and R12 is the current detection resistor. The output voltage of the U1 is the control voltage of the MOS tube Q2, which is known by the concept of the operational amplifier's deficiency. The reverse input voltage of the U1 is equal to the voltage on its forward input, that is, the current on the R12 is controlled by the brightness control voltage, and does not change with the change of the load.

 

Single-chip produces a corresponding luminance control voltage according to the gray value it gets, and also produces a PWM signal. The PWM signal meets the TL431 signal to control the switch of the Q1. Then the MCU changes the duty ratio of the PWM signal according to the LED current signal obtained and changes the output voltage of the switching power supply, that is to change the constant. The input voltage of the flow source reduces the voltage on the power tube Q2, so that it works in the adjustable resistance zone or near the adjustable resistance zone in the case of the constant output current, in order to improve the efficiency. TL431 is the three-terminal adjustable shunt reference, where the existence of TL431 and its corresponding electric phase is to limit the maximum output voltage of the switching power supply and further improve the security of the system.

 

When the light is relatively good, the MCU controls the output of the luminance control voltage according to the gray value obtained, so that the output current of the constant current source is relatively small, and the energy-saving effect can be achieved. In Figure 2, the output voltage of the microcontroller is controlled by D/A to supply the constant current source. Figure 2 does not draw the D/A part.

VII Basic Suggestion for Designing LED Driver

The design of an LED driver is not difficult, but we must have a good idea. As long as we do debug before calculation, debugging and aging after debugging, we believe that anyone can do well in LED.

7.1 LED Current Size

Everyone knows that if the LED ripple is too large, it will affect the life of the LED. As for the impact, there is no specific indicator yet.

7.2 Chip Fever

This is mainly for the high-voltage driver chip with a built-in power modulator, which not only reduces the power consumption of the chip but also does not introduce additional power consumption for heat dissipation.

7.3 Power Tube Fever

The power consumption of the power tube is divided into two parts, switching loss and conduction loss. LED is an electric drive application, and the switch damage is much larger than the conduction loss. The switching loss is related to the CGD and CGS of the power pipe and the driving ability and working frequency of the chip. So solving the heat problem of the power pipe can be solved from the following aspects:

 

A. MOS power tube can not be selected based on the size of the conduction resistance. The smaller the internal resistance, the larger the capacitance of CGS and CGD.

 

B. The rest is frequency and chip drive capability. Here we only talk about the influence of frequency. The frequency is directly proportional to the conduction loss. So when the power tube is heating, we should first consider whether the frequency selection is a bit high. When the frequency is reduced, in order to get the same load capacity, the peak current must be larger or the inductance becomes larger, which may lead to the inductor into the saturation area. If the inductance saturation current is large enough, the CCM (continuous current mode) can be changed into DCM (discontinuous current mode), which requires an increase of load capacitance.

7.4 Frequency reduction of working frequency

Frequency reduction is mainly caused by two aspects. The ratio of input voltage to load voltage is small and system interference is large. For the former, be careful not to set the load voltage too high, though the load voltage is high, the efficiency will be high.

 

For the latter, we can try the following aspects: A, the smallest current set the smallest point; B, wiring clean point, especially the key path of sense; C, the selection of the inductor or the inductance of the closed magnetic circuit; D, RC low pass filter, this effect is a little bad. C is not good consistency, the deviation is a bit big, but it should be enough for lighting.

7.5 The Selection of Inductors or Transformers

As the high power light-emitting diode operating voltage is only 3V, the full-bridge rectifier turns the 220V AC into DC, the voltage drop on the full bridge is about 1.8V. And the power utilization efficiency of only one light-emitting diode is only 60%. We must connect more than 3 light-emitting diodes together to make the total electricity utilization efficiency more than 80%.

 

According to the principle of three basic color synthesis white light, 31W high-power light-emitting diodes with red, green and blue are connected in series, and the brightness of the LED equivalent to the white light of 3W can be obtained. At the same time, 6 kinds of color light can be combined to satisfy people's preference for color conversion.

 AC LED Driver

VIII Conclusion

The LED drive circuit uses a switching power supply as the first level of control, and a pressure control constant current source as the second level of control. Combining the advantages of the two can ensure efficiency and control accuracy. Moreover, it is directly provided by the city with electricity, two-layer drive, high safety, and it is not easy to damage the expensive LED lights. Experiments show that the efficiency of the system can reach more than 83%, and the power is the same as that of a single-ended flyback switching power supply, which is worthy of promotion.

 

Frequently Asked Questions about LED Driver Basics

1. What is an LED driver used for?

LED drivers are devices which regulate and supply the power used to 'drive' runs of LED strip lighting. Similar to traditional transformers, they transform mains voltage alternating current (240v AC) to a lower voltage.

 

2. Do I need a driver for LED lights?

Every LED light source requires a driver. ... Some LEDs already include an integrated driver within the bulb. LEDs designed for household use (bulbs with E26 / E27 or GU24 / GU10 bases and that run on 120V) typically already include a driver. However, low voltage LED light sources, such as some MR- bulbs (MR GU5.

 

3. What is the difference between a transformer and an LED driver?

What's difference between LED driver and LED transformer? A transformer is by convention a double wound device, just ac in, ac out. Drivers are more sophisticated than that and usually give a dc output using a switched-mode system, also they have current regulating and monitoring circuits in them.

 

4. Can a LED driver be used as a power supply?

Constant Voltage LED Drivers. Constant current and Constant voltage drivers are both viable options for a power supply for LED light sources, what differs is the way in which they deliver the power.

 

5. How many LEDs can a driver power?

If you have a driver with a wattage output of 60 watts, it should only operate LEDs that use a combined 48 watts (60w x 80% = 48w). How many lights can one driver power? Drivers are not limited by the number of LED lights they power. They are restricted by the total wattage of the LED lights they power.

 

6. How long does an LED driver last?

Namely, the life of the driving circuit expires prior to when the LED stops emitting light or has its brightness dropped. The typical nominal lifetime of these elements is often times less than 25,000 hours, while the lifetime of LED itself could be as long as 50,000-100,000 hours.

 

7. Do LED drivers get hot?

Heat is the enemy of electronics and this goes for LED drivers too. This doesn't mean that LED drivers cannot operate in hot environments, they can. ... The output capacity of a switch-mode power supply, including LED drivers reduces as the temperature increases.

 

8. How do I choose an LED driver?

Use an LED driver with at least the same value as your LED(s). The driver must have a higher output power than your LEDs require for extra safety. If the output is equivalent to the LED power requirements, it is running at full power. Running at full power may cause the driver to have a shorter life span.

 

9. How do I know if my LED drivers are bad?

LED drivers rectify higher voltage alternating current to low voltage. If you have a good LED and a bad operating LED driver your high bay LED Lights won't be functional for long. Most LED failures are not from the LED, but from the driver. Usually the circuits burn out and fail.

 

10. How does an LED driver circuit work?

In electronics, an LED circuit or LED driver is an electrical circuit used to power a light-emitting diode (LED). ... The voltage drop across an LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current.


Book Recommendation

  • Electronic Drivers for LED Devices, Arrays or Systems (NEMA SSL 1-2010)

--The Association of Electrical Equipment and Medical Imaging Manufacturers (Author)

  • LED Applied Technology Series Books: LED driver power supply design of 100 cases (Chinese) Paperback – 1991

--ZHOU ZHI MIN DENG (Author)

  • Low Cost Low Voltage Low Power Integrated LED Driver Paperback – July 14, 2016

It is quite clear that economic growth is closely linked to energy availability. Energy availability can be approached by two ways; the first way is to build more power plants to cover the increased demand. The second way is to reduce the power consumption. LED lighting has many advantages like high reliability, low maintenance cost, dimming in addition to the main advantage of energy saving and strong expected performance enhancement. On the other hand, the disadvantages are mainly due to the initial cost of changing the lighting systems in addition to the need of a special power electronics circuitry to drive them for regulated intensity and brightness. The project goal is replace the halogen bulbs (50W) to integrated led lamp (10W). LEDs have many advantages when compared with other light sources such as incandescent or fluorescent lamps. The most significant advantages are fast turn-on, lower heat generation, lower power consumption and higher operating life. LEDs need to be driven properly to ensure optimal performance and long life. The driver must be cost effective, which is not usually achieved with discrete components but can be realized with integrated solutions.

--Aya Gebreel Ahmed (Author), Mahmoud Nassary Abd Al-Fattah (Author), Aya Bakr Abd Al-Wahab (Author)


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pinglun 7 comments

    • pingluntus
    • Nama on 2018/4/9 15:20:21

    Good LED Driver article! LED constant current drive has IC and no IC, RC step-down and transformer step-down. Excuse me with IC and not with IC, what is the difference between the use effect, the difference, and the RC depressurization and the transformer depressurization, what is the difference between the use effect and the effect?

      • pingluntu
      • author on 2018/4/9 15:24:26
        author

      Re:

      Hi~ The output current with IC is more stable.

      RC depressurization is resistance resistance and depressurization, generally used in small power, the advantages of low cost, small components, but when the load needs more current, the volume of capacitance will be relatively large, the cost will increase a lot, and the RC is a non isolation power, the security is poor.

      The output power of the transformer can be greatly reduced and the safety is better. When the load power is small, the cost is higher than that of RC.


    • pingluntus
    • ralsa li on 2018/4/9 15:21:55

    Good pages!

    • pingluntus
    • Tomy on 2018/4/9 15:29:20

    The output current reaches 2-3 amperes, and the output voltage is 3-5V. Can you tell me what IC is good for? It's better to input 220V, to output constant current 2.5A, and the lowest output voltage is 3-5V.

      • pingluntu
      • author on 2018/4/9 15:32:05
        author

      Re:

      The parameters are not homogeneous and the input voltage is poor. If DC/DC is buck, AX2003 is recommended, and AX5201 is recommended for DC/DC boost. It is difficult to decide which constant current drive IC will be used for the parameters that have been announced, and what products to use. What are the requirements for the size and external components of the PCB board? They should all be taken into account. Well ,this is my person answer.

    • pingluntus
    • mouser on 2018/4/9 15:35:47

    Hi~@Tomy 3A series LM2596, LM1085, MIC29302, SPX1582, SPX1587, MIC29300, MIC29301 and MIC29303,I think them are worthy to consider. PS: This paper has a vivid clear route to introduce LED driver and driver circuit! I learn a lot from it! Thank you,respected author @author

      • pingluntu
      • author on 2018/4/9 15:37:01
        author

      Re:

      Hi,@mouser

      Thank you for your admire~

    • pingluntus
    • simys on 2018/4/9 15:39:17

    But and I want to know what is the difference between LED constant current drive chip and constant voltage LED drive chip?

      • pingluntu
      • author on 2018/4/9 15:40:45
        author

      Re:

      What is the difference between the LED drive chip and the constant current? The constant current is fixed current, and the voltage is not fixed, which means IC is 74HC595.

      Constant voltage is fixed voltage and current is not fixed, which means IC has MBI5026 and TB62726.

      For the display, constant voltage is more stable than constant current. Most of the LED displays are driven by constant voltage IC.

      The difference between the constant pressure source and the constant current source definition:

      1) the output voltage of constant voltage source is constant under the condition of permissible load.

      It will not change in the load of the Sui Dynasty. It is usually applied to small power LED modules, and there are many aspects of low power LED light bar. Constant voltage source is what we call constant voltage power supply. It can keep voltage unchanged when load (output current) changes.

      2) the output current of constant current source is constant under the condition of permissible load. It will not change according to the load of the Sui Dynasty. It is usually applied to high-power LED products. LED constant current source will also be used in high-end low-power LED products.If you want to lengthen the life of LED products, the choice of LED power is very important, and the constant current source power is the best choice of LED.

      The constant current source can adjust its output voltage correspondingly under the condition of load change, so that the output current remains unchanged. The switching power supply we see is basically constant voltage source.


    • pingluntus
    • nắp rãnh thoát nước bằng gang on 2018/9/13 6:17:16

    Thanks for sharing your thoughts on LED driver. Regards

    • pingluntus
    • Mousa on 2020/8/10 3:47:20

    Good work. However, I still not able to find the cause of Flickering led. I have replaced the 400v and 100v Caps but it still Flickering.

      • pingluntu
      • author on 2020/8/17 10:45:54
        author

      Re:

      I think the possible reasons are:

      1. The LED lamp beads do not match the LED drive power.

      2. The drive power supply is damaged.

      3. If the driver has an over-temperature protection function, and the heat dissipation performance of the material of the lamp cannot meet the requirements, the over-temperature protection of the driver will flash out when it starts to work.

      You need to make sure there is no problem with the circuit where the LED light is there, especially the switch. Then you can check the power converter on the back of the LED light, remove the converter directly, and use a multimeter to measure the voltage or current. If there is no problem with the power converter of the LED, switch the multimeter to the voltage output position, and then place it on the positive and negative poles of the corresponding LED lamp beads to see if it will light up. If not, replace it.


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