Because LED saving, long life, high efficiency photovoltaic numerous advantages to the rapid development in recent years, applications in various industries, LED drive power became concerned about the hot, theoretically, LED life of over 100,000 hours, but in the actual application process In the middle, the LED is extremely vulnerable due to improper selection of the design and driving method of the driving power supply.
When designing the LED driver power supply , it is necessary to know the LED current and voltage characteristics. Due to the different LED manufacturers and LED specifications, the current and voltage characteristics are different. Taking the typical specification of white LED as an example, according to the current and voltage variation rules of LED, the general application forward voltage is about 3.0-3.6V, the typical value is 3.3V, and the current is 20mA. When applied to the forward voltage of the LED. After more than 3.6V, the forward voltage is very small, and the forward current of the LED may increase exponentially, so that the temperature of the LED illuminator rises too fast, thereby accelerating the LED light attenuation, shortening the life of the LED, and even burning when it is serious. Bad LED. According to the voltage and current variation characteristics of the LED, strict requirements are imposed on the design of the driving power supply.
At present, LED lamp products (such as guardrails, lamp cups, and projection lamps) produced by many manufacturers use resistance, capacitance and step-down, and then add a Zener diode to supply power to the LED. This way, there are great defects in the way of driving the LED. First, it is inefficient, consumes a lot of power on the step-down resistor, and may even exceed the power consumed by the LED, and cannot provide a large current drive, because the larger the current, the greater the power consumed by the step-down resistor, so Many products do not dare to use parallel mode, and all use series to reduce current. Secondly, the ability to stabilize the voltage is extremely poor, and it cannot be guaranteed that the LED current does not exceed its normal working requirements. When designing the product, the voltage across the LED is used to drive the power supply, which is at the cost of reducing the brightness of the LED. The LED is driven by the resistance and capacitance step-down mode, and the brightness of the LED cannot be stabilized. When the power supply voltage is low, the brightness of the LED becomes dark, and when the power supply voltage is high, the brightness of the LED becomes brighter. The biggest advantage of resisting and capacitive step-down driving LEDs is low cost.
According to the LED current and voltage variation characteristics, it is feasible to drive the LED with constant voltage. Although the commonly used voltage regulator circuit has the disadvantages of insufficient voltage regulation accuracy and poor current flow capability, it may be designed accurately in some products. The advantage is still that other driving methods cannot be replaced.
The constant current driving method is an ideal LED driving method, which can avoid the current fluctuation caused by the change of the LED forward voltage, and the constant current stabilizes the brightness of the LED. Therefore, many manufacturers choose constant-current mode to drive LEDs. There is also a kind of LED driving method that is feasible. It does not have constant voltage or constant current, but through the design of the circuit, when the forward voltage of the LED rises, the driving current is reduced. Small, to ensure the safety of LED products . Of course, the rise of the forward voltage can only be in 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 type of driving method has advantages and disadvantages. According to the requirements and application of LED products, the LED driving method is reasonably selected, and the precise design of the driving power supply becomes the key.
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