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 supply 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.
LED drive power supply nine performance characteristics requirements
According to the power consumption rules of the power grid and the characteristics of the LED driver power supply, the following nine performance characteristics must be considered when selecting and designing the LED driver power supply:
1. High reliability Especially like the driving power of LED street lights, it is installed at high altitude, it is inconvenient to maintain, 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. High power factor The 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. Drive Mode There are two types of traffic: 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. 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 LED driver power supply must have the ability to suppress the intrusion of surges and protect the LEDs from damage.
6. Protection function 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. Protection aspects The external installation of the lamp, the power structure should be waterproof and moisture-proof, and the 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.
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