LED driver power supply is one of the essential accessories of lamps and lanterns; LED driver power supply is closely related to the power and luminous efficacy of the lamp body, so lighting practitioners should have a more in-depth learning knowledge of LED driver power supply. This article provides some LED drive power-related knowledge for those who are new to the industry.
1，What is the LED driver power supply
LED drive power supply to convert the power supply to a specific voltage current to move the LED light voltage converter, in general: LED go power supply inputs include high-voltage frequency AC (i.e., utility), low-voltage DC, high-voltage DC, low-voltage high-frequency AC (such as the output of electronic transformers), etc.
The output of the LED driver power supply is mostly a constant current source that can change the voltage with the change in the value of the LED forward voltage drop.
LED power supply core components include switching controllers, inductors, switching components (MOSFET), feedback resistors, input filter parts, output filter parts, etc. According to the requirements of different occasions, there are also input overvoltage protection circuits, input under-voltage protection circuits, LED open circuit protection, overcurrent protection, and other courses.
2, the characteristics of the LED driver power supply
(1) High reliability
Especially like the LED street light drive power supply, installed at high altitude, maintenance is not convenient, and maintenance costs are also high.
(2) High efficiency
LED is an energy-saving product, the efficiency of the drive power supply to be high. For the power supply installed in the lamps and lanterns junction, heat dissipation is very important. High efficiency of the power supply, its power dissipation is small, the heat generated in the lamps and lanterns is small, also reduces the temperature rise of the lamps and lanterns. Beneficial to slow down the light decay of LED.
(3) high power factor
Power factor is the power grid requirements for the load. General 70 watts or less of appliances, there are no mandatory indicators. Although the power of a small single appliance power factor is a little lower on the grid, the use of lighting at night, the same kind of load is too concentrated, will produce more severe pollution of the grid. For 30 watts to 40 watts of LED drive power supply, it is said that shortly, there will be specific indicators of power factor requirements.
(4) drive mode
There are two prevailing: one is a constant-voltage source for multiple constant-current sources, each constant-current source separately to each road LED power supply. This way, the combination of flexible, one LED failure does not affect the work of other LEDs, but the cost will be slightly higher. It has the advantage of a little lower price but poor flexibility, and to solve the problem of a LED failure, it does not affect the operation of other LEDs. These two forms, over time, coexist. Multiple constant-current output power supply methods, in terms of cost and performance, will be better. Perhaps the mainstream direction in the future.
(5) Surge protection
LED anti-surge capability is relatively poor, especially the ability to resist reverse voltage. Strengthen this aspect of protection is also very important. Some LED lights are installed in the outdoors, such as LED street lights. Due to the induction of the grid load and lightning strikes, the grid system will invade a variety of surges; some surges will lead to damage to the LED.
(6) protection function
Power supply in addition to the conventional protection function, it is best to increase the LED temperature negative feedback in the constant current output to prevent the LED temperature is too high; to meet the requirements of safety regulations and electromagnetic compatibility.
3, according to the driving mode classification
(1) constant-current type
constant current driver circuit output current is constant, while the output DC voltage varies with the size of the load resistance within a certain range, the load resistance is small, the output voltage is low, the greater the load resistance, the higher the output voltage.
The Constant current circuit is not afraid of the load short circuit, but the load is strictly prohibited completely open circuit.
Constant current driver circuit to drive the LED is a more ideal but relatively high price.
Attention should be paid to the maximum withstand current and voltage value used, limiting the number of LEDs used.
(2) Regulated
When the parameters in the regulated circuit are determined, the output voltage is fixed, while the output current changes with the increase or decrease of the load.
(b) The regulated circuit is not afraid of an open load, but a complete short course of the bag is strictly prohibited.
To drive LEDs with a regulated drive circuit, each string needs to add a suitable resistor to make each series of LEDs show average brightness.
Brightness will be affected by the voltage variation coming from rectification.
4, the overall constant current and constant current by way of working advantages and disadvantages
Compared with the overall constant current, constant current circuit by circuit, although the disadvantages are more, the cost is also relatively high. But it can play a role in protecting the LED and extending the LED's life, so the constant current is the future trend.
5, the shortage of LED power supply
LED drive power supply is currently inadequate for the following reasons.
The production of LED lighting and related products of the company's technical staff do not know enough about switching power supplies to make the power supply can work properly, but some critical assessments and electromagnetic compatibility are not enough to consider; there are still certain hidden dangers.
Most LED power supply manufacturers are transformed from ordinary switching power supplies to do LED power; the characteristics of LED and the use of knowledge is not enough.
At present, there are almost no standards on LED; most of them refer to the means of switching power supplies and electronic rectifiers.
Now, most LED power supplies are not unified, so the volume is mostly relatively minor. Small procurement volume, the price is high, and component suppliers are not very cooperative.
LED power supply stability: broad voltage input, high and low-temperature work, over-temperature, over-voltage protection, and other issues are not solved one by one.
First is the overall life of the driver circuit, especially the critical devices such as capacitors at high temperatures directly affect the life of the power supply.
Is the LED driver should challenge higher conversion efficiency, especially when driving high-power LEDs is even more so, because all the power not dissipated as light output as heat, the power conversion efficiency of the power supply is too low, affecting the energy-saving effect of LEDs.
At present, in minor power (1-5W) applications, the cost of constant current drive power supply has been close to 1/3, is close to the cost of the light source, to a certain extent, affects the market promotion.
