The working principle of LED lamp power driver
LED is a solid light source, when a forward voltage is added to its two ends, the minority carriers and the majority carriers in the semiconductor are recombined, and the excess energy emitted will cause photon emission. Using different materials, it can be made into different colors of light-emitting diodes. LED is a light-emitting diode that has the characteristics of ordinary semiconductor rectifier diodes in addition to its light-emitting properties.
If a lighting fixture is compared to a young girl, then the light distribution is her connotation, the structure is her appearance, and the electronics is her heart. If you don't have a heart, you don't have life, and the role of power in the whole lamp is as important as the heart of a person. A good driving power supply can also determine the life of a lamp product.
Basic characteristics of LEDs
(1) Unidirectional conduction;
(2) LEDs have threshold voltages. The threshold voltage of the LED and the forward voltage drop during normal operation are related to the light color of the LED.
(3) It has a nonlinear volt-ampere characteristic curve, and the current is not proportional to the voltage;
(4) The LED luminous flux increases with the increase of current, but it is not proportional;
(5) Sensitive to temperature, when the temperature rises, the light output decreases, and the forward voltage decreases;
(6) The discreteness is large.
Basic operating conditions for LEDs
(1) The input DC voltage is not lower than the forward voltage drop of the LED;
(2) Driven by DC current or unidirectional pulse current;
(3) Limit the LED current to prevent LED damage;
(4) Due to the nonlinear relationship between the LED current and its luminous flux, the LED should work at a current value with a high luminous efficiency ratio;
(5) Excellent heat dissipation design.
As the core component of LED lamps, LED power supply is like the heart of LED, and the quality of LED drive power supply directly determines the quality of LED lamps. First of all, in terms of structural design, the outdoor LED driver must have a strict waterproof function, otherwise, it cannot withstand the harsh use environment outside.
Secondly, the lightning protection function of the LED driver is also crucial. If the driving power supply has no lightning protection function, it will directly affect the life of LED lamps and increase the maintenance cost of lamps.
Finally, in the selection of raw materials, their reliability must meet their life requirements, and their functional characteristics must be good enough.
LED power supply can be divided into two categories according to the driving mode:
1. Constant current type:
1. The constant current drive circuit is ideal to drive the LED, and the disadvantage is that the price is higher.
2. Although the constant current circuit is not afraid of short circuit of the load, it is strictly forbidden to completely open the load.
3. The output current of the constant current drive circuit is constant, while the output DC voltage changes within a certain range with the different size of the load resistance.
4. The number of LEDs should be limited, because it has the maximum current and voltage value.
2. Voltage stabilization:
1. After the voltage stabilizing circuit determines the parameters, the output is a fixed voltage, but the output current changes with the increase or decrease of the load.
2. Although the voltage regulator circuit is not afraid of open circuit of the load, it is strictly forbidden to completely short circuit the load.
3. The voltage change after rectification will affect the brightness of the LED.
4. In order to make the brightness of each string drive LED with a voltage regulator circuit to display uniformly, it is necessary to add a suitable resistor.
Why do LEDs use constant current power supplies?
The volt-ampere characteristics of LEDs are not fixed, they change with temperature, so when the constant voltage power supply, the LED current changes with the change of temperature, because the volt-ampere characteristics of LEDs have the characteristics of negative temperature coefficient.
The quality of LED power supply directly restricts the reliability of LED products, therefore, foreign customers in the international market have a good interest in LEDsThe requirements for efficiency conversion, effective power, constant current accuracy, power supply life, and electromagnetic compatibility of the drive power supply are very high. A brief introduction to the key technical parameters of the power drive:
【Input Voltage】
That is, the voltage value required for the normal operation of LED lamps and lanterns, according to different countries have different input voltage values, we usually refer to the civil full voltage is AC85~264V.
【Input power】
Input power refers to the product of the input voltage and input current of various electrical devices, that is, the power of the power supply or power grid to provide electrical energy to various electrical devices.
【Power Factor】
Also known as power factor, the English abbreviation PF (Power Factor) is the ratio of active power to apparent power. To a certain extent, the power factor reflects the proportion of electric energy that can be utilized, and is an important indicator of rational electricity consumption.
The low power factor indicates that the driving power supply and circuit design used are not good, which will greatly reduce the service life of the lightingThe power factor is low, and the life of the lighting will not be long, no matter how good the lamp beads are. The power factor can be detected with the "power factor table"!Generally, the power factor of export LED panel lamps is required to reach more than 0.85. The power factor is less than 0.5, it should be said that unqualified products or garbage products not only have a short life, but also the actual power consumption is about twice as high as the nominal one, that is, compared with ordinary energy-saving lamps, there is no power saving at all!
【Constant current accuracy】
Constant current accuracy refers to the ratio of the output current fluctuation value to the rated output current when the input voltage of the driving power supply changes within a certain range, which is usually expressed as a percentageFor example, the rated output current of an LED driver power supply is 0.45A, when the input voltage is inAC80~264VWhen changing, the measured output current varies between 0.43-0.45, then the constant current accuracy=(0.45-0.43)÷0.45≈0.045 =4.5%.The higher the constant current accuracy, the more stable the LED operation is,Otherwise, there will be a flicker phenomenon and, more seriously, LED failure.
【Electromagnetic Compatibility】
Electromagnetic compatibility (EMC) refers to the ability of a device or system to work normally in the electromagnetic environment in which it is located and not to cause unbearable electromagnetic disturbance to anything else in the environment (such as causing the radio to be unable to play normally, causing noise in the TV screen, etc.).