I.LED street light waterproof power supply is one of the LED drive power supply, is to put the power supply is converted into a specific voltage current to drive the LED voltage converter, normally: LED street light waterproof power input includes high voltage power frequency ac (mains), low voltage, high voltage direct current, low voltage high frequency ac dc (such as the output of electronic transformer). The output of LED drive power is mostly a constant current source that can change the voltage with the change of LED forward voltage drop value.
According to the power grid rules and the characteristics of LED street lamp waterproof power supply, the following points should be considered in the selection and design of LED drive power supply:
1. High reliability is especially like the driving power supply of LED street lamp, which is installed in the high altitude, which is inconvenient to repair and costs a lot.
2. High efficiency LED is energy saving product, the efficiency of driving power supply is high. It is particularly important for the structure of the power source installed in the lamp. Because the luminous efficiency of LED decreases with the increase of LED temperature, the cooling of LED is very important. The efficiency of the power supply is high, its consumption power is small, the heat in the lamp is small, also reduced the temperature rise of the lamp. It is beneficial to delay LED light decay.
3. High power factor power factor is the load requirement of power grid. General 70 watts of electrical appliances, no mandatory indicators. Although the power factor of individual electrical appliances with small power is a little lower on the impact of the grid, but at night we light, the same load is too concentrated, will produce serious pollution to the grid. For the 30-40 watt LED drive power supply, it is said that in the near future, there may be certain power factor requirements.
4. Currently, there are two driving modes: one is a constant voltage source to supply multiple constant current sources, and each constant current source alone provides power to each LED. In this way, the combination is flexible, and the LED failure will not affect the work of other leds, but the cost will be slightly higher. The other is direct constant current power supply, LED series or parallel operation. Its advantage is low cost, but poor flexibility, but also to solve one LED fault, does not affect the operation of other LED problems. These two forms coexist for a period of time. Multi-channel constant current output power supply mode, in terms of cost and performance will be better. Maybe it's going to be the mainstream.
5. Surge protection LED anti - surge ability is relatively poor, especially anti - reverse voltage ability. Strengthening protection in this area is also important. Some LED lights are installed outdoors, such as LED street lamps. Due to the swing of power grid load and the induction of lightning strike, various surges will be invaded from the power grid system, and some surges will lead to the damage of LED. Therefore, LED drive power should have the ability to suppress the invasion of surge and protect LED from being damaged.
6. In addition to the conventional protection function, it is better to add negative feedback of LED temperature in constant current output to prevent LED temperature from being too high.
7. Protection outside the lamp installation type, power structure to waterproof, moistureproof, shell to be light resistant.
8. The life of the drive power should match the life of the LED.
9. To meet the requirements of safety and electromagnetic compatibility.
With the wide application of LED, the performance of LED drive power supply will be more and more suitable for the requirements of LED.
According to the driving mode, it can be divided into two categories:
(1) constant current:
A. The constant current driving circuit output current is constant, while the output dc voltage varies within a certain range with different load resistance value. Small load resistance value leads to low output voltage, and the larger the load resistance value leads to higher output voltage.
B. Constant current circuit is not afraid of load short circuit, but it is forbidden to completely open the load.
C, constant current drive circuit drive LED is relatively ideal, but relatively high price.
D. Attention should be paid to the maximum withstand current and voltage value, which limits the number of LED;
(2) stable voltage:
A. when the parameters of the voltage regulator circuit are determined, the output voltage is fixed, while the output current changes with the increase or decrease of the load;
B. The voltage regulator circuit is not afraid of open circuit under load, but it is strictly prohibited to have complete short circuit under load.
C. Drive LED with voltage stabilizing drive circuit. Each string needs to be added with appropriate resistance to make each string of LED display brightness average;
D. Brightness will be affected by the voltage change from rectification.
Classified by circuit structure
(1) voltage step-down mode of resistance and capacitance:
By using capacitor to reduce voltage, when flashing, due to the action of charging and discharging, the instantaneous current through LED is extremely large, which is easy to damage the chip. Vulnerable to power grid voltage fluctuations, low efficiency and reliability of power supply.
(2) resistance step-down mode:
It is not easy to make voltage stabilized power supply through resistance step-down, which is greatly affected by the change of grid voltage. Step-down resistance consumes a large part of energy, so the power supply efficiency of this power supply mode is very low, and the reliability of the system is also low.
(3) conventional transformer step-down mode:
Power supply volume is small, weight lay particular stress on, power efficiency is very low also, have 45% ~ 60% only commonly, use rarely commonly so, reliability is not high.
(4) step-down mode of electronic transformer: the power supply efficiency is low, the voltage range is not wide, generally 180 ~ 240V, ripple interference is large.
(5) RCC step-down switching power supply:
Wide voltage range, high power efficiency, generally can achieve 70% ~ 80%, wide application. As the oscillation frequency of this control mode is discontinuous, the switching frequency is not easy to control, the ripple coefficient of load voltage is relatively large, and the adaptability of abnormal load is poor.
(6) PWM control mode switching power supply:
It is mainly composed of four parts: input rectifier and filter part, output rectifier and filter part, PWM voltage regulator control part, switching energy conversion part. The basic working principle of PWM switching voltage stabilizer is changes in input voltage, the parameters of internal and external load, the control circuit by the control signal and reference signal difference of closed loop feedback, adjust the main circuit switching device turn-on, the pulse width of the makes switch power supply output voltage or current stability (i.e., the corresponding regulated power supply and constant current power supply). High efficiency of power supply, generally 80% ~ 90%, stable output voltage and current. Generally this kind of circuit has perfect protection measures, belongs to the high reliability power supply.