Due to many advantages such as environmental protection, long life and high photoelectric efficiency, LED has been rapidly developed in various industries in recent years. The driving power of LED has become a hot spot. In theory, the service life of LED is more than 100,000 hours, but in the actual application process In the case, the design of the driving power and the improper selection of the driving method make the LED extremely vulnerable.
When designing LED drive power, it is necessary to know the LED current and voltage characteristics. Due to different LED manufacturers and LED specifications, current and voltage characteristics are different. Now taking the typical specifications of white LED as an example, according to the LED current and voltage changes, the general application of forward voltage is about 3.0-3.6V, the typical value is 3.3V, the current is 20mA, when the forward voltage across the LED After exceeding 3.6V, the forward voltage will increase very little, and the forward current of the LED may multiply, making the temperature of the LED luminous body rise too fast, thereby accelerating the LED light attenuation, shortening the life of the LED, and even burning in severe cases. Bad LED. According to the characteristics of LED voltage and current changes, strict requirements are imposed on the design of the driving power supply.
At present, many manufacturers of LED lamp products (such as guardrails, lamp cups, and projection lamps) use resistance and capacitance to reduce voltage, and then add a voltage stabilizing diode to stabilize the voltage to supply power to the LED. This way of driving the LED has great defects. First, the efficiency is low, a large amount of power is consumed in the buck resistor, and it may even exceed the power consumed by the LED, and it cannot provide a large current drive, because the larger the current, the greater the power consumed in the buck resistor, so LEDs of many products do not dare to use parallel connection, but all use series connection to reduce current. Secondly, the ability to stabilize the voltage is extremely poor, and it cannot be guaranteed that the current through the LED will not exceed its normal working requirements. When designing the product, the voltage at both ends of the LED will be reduced to power the drive. This is at the cost of reducing the brightness of the LED. The LED is driven by resistance and capacitive voltage reduction. The brightness of the LED is not stable. When the power supply voltage is low, the brightness of the LED becomes darker. When the power supply voltage is high, the brightness of the LED becomes brighter. The biggest advantage of resistive and capacitive buck driving LED is low cost.
According to the characteristics of LED current and voltage changes, it is feasible to use constant voltage to drive LEDs. Although the commonly used voltage stabilizing circuits have the disadvantages of insufficient voltage stabilizing accuracy and poor current stabilizing ability, they may be over-precisely designed in the application of certain products. , Its advantages are still irreplaceable by other driving methods.
The constant current drive mode is an ideal LED drive mode. It can avoid the current fluctuation caused by the change of the LED forward voltage, and the constant current makes the brightness of the LED stable. Therefore, many manufacturers choose to drive LEDs in a constant current mode. There is also an LED drive mode that is not constant voltage or constant current, but through the design of the circuit, when the LED forward voltage increases, the drive current is reduced Small, to ensure the safety of LED products. Of course, the increase of the forward voltage can only be within the range of the LED, and too high will damage the LED.
The ideal LED driving method is to use constant voltage and constant current. But the cost of the drive increases. In fact, each driving method has advantages and disadvantages. According to the requirements of LED products and application occasions, it is reasonable to choose the LED driving method and accurately design the driving power supply.
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