LED drive power, how much do you know?

1. What is the LED driver power supply?
The LED drive power source converts the power supply into a specific voltage and current to drive the LED light-emitting voltage converter. Usually, the input of the LED drive power source includes high-voltage power frequency AC (ie, mains), low-voltage DC, high-voltage DC, low-voltage high-frequency. AC (such as the output of an electronic transformer). The output of the LED driver is mostly a constant current source that changes the voltage as the LED's forward voltage drop changes. The core components of the LED power supply include a switch controller, an inductor, a switching component (MOSfet), a feedback resistor, an input filter component, an output filter component, and the like. According to the requirements of different occasions, there are also input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.
2, LED drive power features (1) high reliability, especially like the LED street light drive power, installed at high altitude, maintenance is not convenient, maintenance costs are also large.
(2) High efficiency
LEDs are energy-saving products, and the efficiency of driving power supplies is high. It is very important to dissipate heat from the power supply installed in the fixture. The power supply has high efficiency, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LEDs.
(3) High power factor The power factor is the load requirement of the grid. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the power factor of a single power consumer with low power has little effect on the power grid, the amount of lighting used at night is large, and the similar load is too concentrated, which will cause serious pollution to the power grid. For 30 watts to 40 watts of LED driver power, it is said that in the near future, there may be certain indicators for power factors.
(4) There are two types of driving methods: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. In this way, the combination is flexible, and all the LED faults do not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, which is the drive mode adopted by “Zhongke Huibao”. The LEDs run in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and it is necessary to solve a certain LED failure without affecting the operation of other LEDs. These two forms coexist for a while. Multi-channel constant current output power supply mode will be better in terms of cost and performance. Perhaps it is the mainstream direction in the future.
(5) Surge protection
The ability of LEDs to withstand surges is relatively poor, especially against reverse voltage capability. It is also important to strengthen protection in this area. Some LED lights are installed outdoors, such as LED street lights. Due to the start of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause LED damage. Therefore, the analysis of the "Zhongke Huibao" drive power supply should have a certain lack of surge protection, and as the power supply and lamps are frequently replaced, the LED drive power supply must have the ability to suppress the intrusion of surges and protect the LED from damage.
(6) Protection function power supply In addition to the conventional protection function, it is better to increase the LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high; it is required to meet the safety and electromagnetic compatibility requirements.
3. Classification according to driving mode (1) The current output by the constant current constant current driving circuit is constant, and the output DC voltage varies within a certain range according to the magnitude of the load resistance value, and the load resistance is small, and the output voltage is small. Low, the greater the load resistance, the higher the output voltage;
The constant current circuit is not afraid of load short circuit, but it is forbidden to completely open the load;
The constant current driving circuit drives the LED, which is ideal, but relatively high in price;
Attention should be paid to the maximum withstand current and voltage values ​​used, which limits the number of LEDs used.
(2) Voltage regulation When the parameters in the voltage regulator circuit are determined, the output voltage is fixed, and the output current changes with the increase or decrease of the load;
The voltage regulator circuit is not afraid of the load open circuit, but it is forbidden to completely short the load;
Driving the LED with a voltage-stabilized driving circuit, each string needs to be added with a suitable resistor to make each string of LEDs display brightness average;
The brightness is affected by the rectified voltage changes.
4. The advantages and disadvantages of the overall constant current and the constant current mode are compared with the overall constant current. Although the constant current is more disadvantageous, the cost is higher. But it can really protect the LED and extend the life of the LED, so the constant current is the future trend.
5, the shortage of LED power
LED driver power supply currently has insufficient reasons:
The technicians of the company producing LED lighting and related products have insufficient understanding of the switching power supply, and the power supply can work normally, but some key evaluations and electromagnetic compatibility considerations are not enough, and there are certain hidden dangers;
Most of the LED power supply manufacturers are transforming from ordinary switching power supplies to do LED power supply, and the characteristics and use of LEDs are not enough;
At present, there are almost no standards for LEDs, and most of them are standards for reference switching power supplies and electronic rectifiers;
Most LED power supplies are not unified now, so most of them are relatively small. The purchase volume is small, the price is high, and the component suppliers are not very cooperative;
The stability of the LED power supply: wide voltage input, high temperature and low temperature operation, over temperature, over voltage protection and other issues are not solved one by one;
The first is the overall life of the driver circuit, especially the key components such as: the life of the capacitor at high temperatures directly affects the life of the power supply;
LED drivers should challenge higher conversion efficiency, especially when driving high-power LEDs , because all power that is not used as light output is dissipated as heat, and the power conversion efficiency is too low, which affects the energy-saving effect of LEDs. Play
At present, in the application of low power (1-5W), the proportion of constant current driving power supply has been close to 1/3, which is close to the cost of the light source, which has affected the market to some extent.

Two major categories of LED drive power
The LED driving power supply is a voltage converter that converts the power supply into a specific voltage and current to drive the LED to emit light. Usually, the input of the LED driving power source includes high-voltage power frequency alternating current (ie, mains), low-voltage direct current, high-voltage direct current, low voltage high. Frequency communication (such as the output of an electronic transformer). The output of the LED driver is mostly a constant current source that changes the voltage as the LED's forward voltage drop changes.
Since the performance and conversion efficiency of LED power supplies of different specifications are different, it is necessary to select a suitable and efficient LED dedicated power supply to truly reveal the high-performance characteristics of the LED light source. Because the low-efficiency LED power supply itself needs to consume a large amount of power, it is impossible to highlight the energy-saving characteristics of the LED in the process of supplying power to the LED. In short, the LED power supply has an important role in the stability, energy saving and long life of the LED.
What are the classifications of LED power supplies?
First, the LED power supply can be divided into two categories according to the driving method:
A. Voltage regulation:
1. After the voltage regulator circuit determines various parameters, the output is a fixed voltage, and the output current changes with the increase or decrease of the load.
2. Although the voltage regulator circuit is not afraid of the load open circuit, it is forbidden to completely short the load.
3. The voltage change after rectification will affect the brightness of the LED.
4, to make each string with the voltage regulator circuit to drive the LED display brightness uniform, you need to add the appropriate resistance before you can
B. Constant current type:
1, constant current drive circuit to drive LED is very ideal, the disadvantage is that the price is higher
2. Although the constant current circuit is not afraid of load short circuit, it is forbidden to completely open the load.
3. The current output by the constant current drive circuit is constant, and the output DC voltage varies within a certain range depending on the magnitude of the load resistance.
4, to limit the number of LEDs used, because it has the maximum withstand current and voltage values. Second, LED power can be divided into six categories according to the circuit structure:
1. Conventional transformer step-down:
The advantage of this kind of power supply is that it is small in size. The disadvantage is that the weight is heavy and the power supply efficiency is very low. Generally, it is 45%~60%. Because the reliability is not high, it is rarely used.
2, capacitor step-down:
The LED power supply in this way is easily affected by the voltage fluctuation of the power grid, and the power supply efficiency is low. It is not suitable for the LED to be used when flashing, because the circuit is stepped down by the capacitor, and when the flashing is used, the instantaneous current through the LED is due to the charge and discharge. Great, easy to damage the chip.
3, electronic transformer step-down:
The insufficiency of this power structure is that the conversion efficiency is low, the voltage range is narrow, generally 180~240V, and the ripple interference is large.
4, resistance buck:
This type of power supply is very inefficient and the system is less reliable. Because the circuit is stepped down by the resistor, it is greatly interfered by the change of the grid voltage, it is not easy to make a regulated power supply, and the step-down resistor itself consumes a large part of the energy.
5, RCC step-down switching power supply:
The advantage of this type of LED power supply is that the voltage regulation range is relatively wide and the power supply efficiency is relatively high, generally 70%~80%, and the application is wide. The disadvantages are mainly that the switching frequency is not easy to control, the load voltage ripple coefficient is large, and the load adaptability of the abnormal situation is poor.
6, PWM control type switching power supply:
At present, the LED power supply designed by the PWM control method is ideal because the output voltage or current of the switching power supply is stable. The power conversion efficiency is extremely high, generally up to 80% to 90%, and the output voltage and current are very stable. The LED power supply of this mode is mainly composed of four parts: an input rectification filtering part, an output rectification filtering part, a PWM voltage regulation control part, and a switching energy conversion part. Moreover, this circuit has perfect protection measures and is a highly reliable power supply.

The nine performance characteristics of the LED driver power supply require the following nine performance characteristics when selecting and designing the LED driver power supply according to the power usage rules of the power grid and the characteristics of the LED driver power supply:
1. The high reliability is especially like the driving power of the LED street lamp. It is installed at a high altitude, the maintenance is inconvenient, and the maintenance cost is also large.
2. High-efficiency LEDs are energy-efficient products that drive power supplies with high efficiency. It is especially important for structures where the power supply is installed in the luminaire. Since the luminous efficiency of the LED decreases as the temperature of the LED increases, the heat dissipation of the LED is very important. The power supply has high efficiency, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LEDs.
3. The high power factor power factor is the grid's load requirements. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the power factor of a single power consumer with low power has little effect on the power grid, at night, everyone lights up, and the similar load is too concentrated, which will cause serious pollution to the power grid. For 30 watts to 40 watts of LED driver power, it is said that in the near future, there may be certain indicators for power factors.
4. There are two types of driving methods: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. In this way, the combination is flexible, and all the LED faults do not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current supply, with LEDs running in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and it is necessary to solve a certain LED failure without affecting the operation of other LEDs. These two forms coexist for a while. Multi-channel constant current output power supply mode will be better in terms of cost and performance. Perhaps it is the mainstream direction in the future.
5. The ability of surge protection LEDs to resist surges is relatively poor, especially against reverse voltage capability. It is also important to strengthen protection in this area. Some LED lights are installed outdoors, such as LED street lights. Due to the start of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause LED damage. Therefore, the LED driver power supply must have the ability to suppress the intrusion of surges and protect the LEDs from damage.
6. Protection function power supply In addition to the conventional protection function, it is better to increase the LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high.
7. For the protection aspect of the lamp, the power supply structure should be waterproof and moisture-proof, and the outer casing should be light-resistant.
8. The life of the drive power is adapted to the life of the LED.
9. To comply with safety and electromagnetic compatibility requirements.
With the increasing use of LEDs, the performance of LED drive power will be more and more suitable for LED requirements.
Seven principles for determining the quality of LED drive power
1. Give up 4 or more outputs, develop single or two outputs, abandon large currents and large currents, and develop small currents.
The more the number of output channels is more complicated, the current interference between different outlets is solved, and the cost is high. If not solved, the failure rate is high. In addition, the more the number of output channels, the larger the total output current, and the current is the main cause of heat generation. The voltage itself does not directly cause heat. Simply speaking, the heat is proportional to the square of the current, that is, the current increases to the original. 2 times, the heat will increase to 4 times, the current will increase to 3 times, and the heat will increase to 9 times. In summary, the single- or two-output LED lamp power failure rate will be much lower.
2, intelligent control is one of the advantages of LED lamps, and power is the key to intelligent control.
Intelligent control is the most mature condition in LED street light and LED tunnel light lighting application. Intelligent control can realize stepless control of lamp power according to road traffic density in different time periods, which not only meets application requirements, but also realizes huge energy saving. The effect can save a lot of money for the highway supervisory unit. The application in tunnel lighting not only saves energy, but also automatically adjusts the brightness of the tunnel entrance and exit according to the brightness outside the tunnel, providing the driver with a visual over-stage to ensure driving safety.
3, give up high power, super high power, choose a medium and small power supply with higher stability.
Because the greater the power, the greater the heat, the more compact the components inside, which is not conducive to heat dissipation, and the temperature is the culprit of power failure. Moreover, the low-power power supply is relatively mature in development, and has advantages in terms of stability and cost. In fact, many high-power power solutions have not been time-tested and proven in practice. They are all rushed projects, all of which are experimental products, so the faults are endless. In contrast, small and medium-sized power supplies have matured due to their earlier development.
4. Heat dissipation and protection are the main external factors of power failure.
Not only the power supply itself will heat up, but also the lamps will heat up. How to properly dissipate these two heat sources is a problem that the lighting design engineer must consider. It is necessary to prevent excessive heat concentration, form a heat island effect, and affect the life of the power supply. A split power solution is a good choice.
5. Feasibility of maintenance.
The problem of power failure cannot be completely avoided. Chengdu Chaoyue Optoelectronics proposed the principle of maintenance simplicity. Only when the replacement of the power supply is made as simple as the replacement of the light source of the conventional illumination can the user be happy, even if the power supply is broken, the mood will not be too bad, and the user's mood determines the LED lamp manufacturer. fate.
6, protection performance.
The protection problem is also very important. The penetration of moisture may cause short circuit of the power supply. The dust on the outer casing will affect the heat dissipation of the power supply. Exposure will easily cause high temperature and aging of wires and other components. From the experience in actual use, the rotation The failure rate of the wiring plug is high, and most of them are faults caused by water leakage.
7, modular design.
Modular design has become the trend of today. It is necessary to find a way to integrate the module power supply. If the power supply can solve the maintenance problem by plugging and unplugging, it will be welcomed by users. At the same time, it is necessary to establish interface standardization for different manufacturers. LED light power can be used universally.
Summary: LED light power supply is best to use split design, while paying attention to the reliability and life of the power supply, even if it adds a little cost, only by standing from the customer's point of view to design the product, the enterprise can get long-term development.