What's the difference between LED power supply and ordinary power supply?

2020-01-03 16:48:07

LED drive supply converts the power supply to a specific voltage or current to drive the LED's luminous voltage converter. In general, the input of LED drive supply includes high-voltage power frequency ac (i.e., mains), low-voltage dc, high-voltage dc, low-voltage high-frequency ac (e.g., output of electronic transformers), etc. The output of LED drive power supply is mostly a constant current source that can change the voltage with the change of LED forward voltage drop. The core components of LED power supply include switch controller, inductor, switching element (MOSfet), feedback resistance, input filter, output filter, and so on. According to the requirements of different occasions, but also input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection circuit.

2. Characteristics of LED drive power supply

(1) high reliability, especially like the driving power supply of LED street lamps, is installed at high altitude, so it is inconvenient to repair and expensive to repair.

(2) high-efficiency LED is an energy-saving product, so the efficiency of driving power should be high. It is very important for the power installed in the lamp junction cooling. The efficiency of power supply is high, its consumption power is small, calorific value is small inside lamps and lanterns, also reduced the temperature rise of lamps and lanterns. It is beneficial to delay the light decay of LED.

(3) high power factor power factor is the load requirement of the power grid. Generally, there is no mandatory quota for electrical appliances under 70 watts. Although the low power factor of a single electrical appliance with low power has little influence on the power grid, the large amount of lighting used at night and the concentrated load of the same kind will cause serious pollution to the power grid. For 30 watts to 40 watts of LED drive power supply, it is said that in the near future, there may be certain requirements for power factors.

(4) there are two driving modes in use: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED individually. This way, the combination is flexible, LED failure along the way, does not affect the work of other LED, but the cost will be slightly higher. The other is direct constant-current power supply, which is the driving mode adopted by "zhongke huibao", LED series or parallel operation. It has the advantage of low cost, poor flexibility, and the ability to solve one LED failure without affecting the operation of other leds. These two forms, for a while, coexist. Multi-channel constant current output power supply, in terms of cost and performance will be better. Maybe it is the mainstream direction in the future.

(5) surge protection LED has poor anti-surge ability, especially anti-reverse voltage ability. It is also important to strengthen protection in this regard. Some LED lights are installed outdoors, such as LED streetlights. Due to the start and drop of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, some of which will cause damage to the LED. Therefore, the analysis of "zhongke huibao" drive power supply in the surge protection should have some deficiencies, and as for the power supply and lamp frequent replacement, LED drive power should have the ability to suppress the invasion of the surge, protect the LED from damage.

(6) protection function in addition to the conventional protection function, it is better to add negative feedback of LED temperature in the constant current output to prevent excessive LED temperature; To meet safety and electromagnetic compatibility requirements.

3. According to the driving mode, it can be divided into two categories:

 

A. The output current of the constant-current drive circuit is constant, while the output dc voltage varies within a certain range with the size of the load resistance value. If the load resistance value is small, the output voltage will be low.
B. The constant current circuit is not afraid of short circuit of load, but it is strictly forbidden to open the load completely.
C. constant current drive circuit drives LED is ideal, but relatively expensive.
D. attention should be paid to the maximum allowable current and voltage values used, which limit the number of leds used.

(2) stabilized voltage:

A. When the parameters in the voltage stabilizing circuit are determined, the output voltage is fixed, while the output current varies with the increase or decrease of the load;
B. The voltage stabilizing circuit is not afraid to open the load, but it is strictly forbidden to short the load completely.
C. Drive the LED with stable voltage drive circuit. Each LED should be equipped with appropriate resistance to make the display brightness of each LED average;
D. the brightness will be affected by the voltage change caused by the rectification.

 

4. For LED street lamp driving power supply, there are two types of constant-current power supply in the market: overall constant-current power supply and circuit-by-circuit constant-current power supply.
The whole constant current by constant current

Advantages and disadvantages advantages and disadvantages

1. Low cost.
2. Emc is easy to handle.
3. LED light source board is easy to design and can be directly connected in parallel.
4. The overall efficiency can reach more than 90%
5. Wiring is easy, the light source board only needs 2 wires. 1. The consistency of LED VF value is required to be very high, otherwise the current will be unbalanced and damaged. 1. The VF consistency of LED is not highly required, and the current of each circuit is very average. LED work more reliable. 1. High cost.
2. Electromagnetic compatibility is not easy to handle.
3. The overall efficiency is not high, up to 85%
4. Wiring is easy, the light source board only needs 2 wires.
It can also be seen from the above comparison that the constant current by road has more disadvantages and higher costs. But it can really protect leds and extend their life, so constant current is the future.
To achieve a higher stability of constant current source power, the specific are:
4.1 high stability, high power factor.
4.2 long life, at least 5000 hours.
4.3 higher overall efficiency.
4.4 strong environmental adaptability. Such as working environment temperature -20-60 degrees lightning strike 4KV.
4.5 waterproof grade shall be above IP66.

In response to the above requirements to solve the following problems.
A. For high power factor and efficiency, LLC is relatively efficient but not stable. Because it depends on the transformer leakage resonance work. The efficiency of forward excitation and synchronous rectifier is also higher, but the technology of forward excitation synchronous rectifier is more complex. Compared with the above two kinds of quasi-resonant and synchronous rectifier, the efficiency is slightly lower, but the stability is good, the scheme is mature. So choose quasi - resonance plus synchronous rectifier.

B. Because the scheme of quasi-resonance plus synchronous rectifier cannot be without electrolytic capacitor. So in the design and components to choose a relatively large margin, high life electrolytic capacitor. At the same time, in order to meet the requirements of the working environment, the components used should be selected at least -20-105 degrees of temperature resistance.
C. Lightning protection circuit and EMC filter circuit shall be added at the input end to meet the requirements of electromagnetic compatibility and lightning strike. Some of the high frequencies are also shielded.
D. The power supply shall be treated with glue to meet the requirements of IP protection level.
5. Current status of LED power supply
LED power supply is also a supporting product. At present, the quality of power supply in the market is uneven. Based on the query of existing data and the bad light problem encountered in the implementation of the project, the reasons for the current shortage of LED drive power are analyzed:

 

A. The technical staff of the company that produces LED lighting and related products do not know enough about the switching power supply, so the power supply can work normally. However, some critical assessment and consideration of electromagnetic compatibility are not enough, so there are still some hidden dangers.
B. Most LED power supply manufacturers have transformed from ordinary switching power supply to LED power supply, so they do not know enough about the characteristics and use of LED.
C. Currently, there are almost no standards for LED, most of which refer to the standards of switching power supply and electronic rectifier.
D. Most LED power supply is not unified, so the quantity is relatively small. The purchase volume is small, the price is high, and component suppliers are not very cooperative.
E. Stability of LED power supply: wide voltage input, high and low temperature operation, overtemperature and overvoltage protection and other problems have not been solved one by one.