Classification and selection of LED power supply

There are many ways to classify LED power supplies:

According to the different output characteristics, it can be divided into constant voltage series and constant current series;

According to different input characteristics, it can be divided into ordinary series and high power factor series;

According to different uses, it is divided into waterproof series and non-waterproof series;

According to the circuit structure, it can be divided into isolation series and non-isolation series;

According to different control methods, it can be divided into dimmable series and non-dimming series.

Due to the many advantages of LED such as environmental protection, long life, and high photoelectric conversion efficiency, in theory, the service life of LED is more than 100,000 hours. However, in actual application, due to improper design of the driving power supply and driving mode selection, or mismatch with LED lamps, the LED is easily damaged or the light decay is very serious, reducing the reliability of LED lamps.

Due to the different manufacturers and specifications of LEDs, the current and voltage characteristics are different. Taking the typical specifications of white light LEDs as an example, according to the current and voltage variation law of LEDs, the forward voltage is generally applied to be around 3.0-3.6V, the typical voltage is 3.3V, and the current is 20mA. When the forward voltage applied to both ends of the LED exceeds 3.6V, a small increase in the forward voltage may double the forward current of the LED, causing the temperature of the LED light source to rise too fast, thereby accelerating the LED light attenuation, shortening the life of the LED, and even burning the LED in severe cases. According to the voltage and current variation characteristics of the LED, strict requirements are put forward for the design of the driving power supply.

At present, many manufacturers produce LED lighting products (such as guardrails, lamp cups, and projection lamps) that use resistors and capacitors to reduce voltage, and then add a voltage regulator diode to stabilize the voltage to supply power to the LED. This way of driving LEDs has great defects. First, the efficiency is low, and a large amount of power is consumed on the voltage-reducing resistor, which may even exceed the power consumed by the LED, and it cannot provide high-current drive, because the larger the current, the greater the power consumed on the voltage-reducing resistor. Therefore, many products do not dare to use the parallel connection method for LEDs, and all use the series connection method to reduce the current. Secondly, the ability to stabilize voltage is extremely poor, and it is impossible to ensure that the current passing through the LED does not exceed its normal working requirements. When designing products, they will use the method of reducing the voltage across the LED to power the drive, which is at the cost of reducing the brightness of the LED. When driving LEDs using the resistor and capacitor voltage-reducing method, the brightness of the LED cannot be stable. When the power supply voltage is low, the brightness of the LED becomes dim, and when the power supply voltage is high, the brightness of the LED becomes brighter. The biggest advantage of driving LEDs using the resistor and capacitor voltage-reducing method is low cost.

According to the characteristics of LED current and voltage changes, it is feasible to use constant voltage to drive LED. Although the commonly used voltage stabilization circuit has the disadvantages of insufficient voltage stabilization accuracy and poor current stabilization ability, it may be over-precisely designed in the application of some products, and its advantages are still irreplaceable by other driving methods.

The constant current driving method is an ideal LED driving method. It can avoid the current fluctuation caused by the change of LED forward voltage. At the same time, the constant current makes the brightness of LED stable. Therefore, many manufacturers choose constant current driving LED.

However, since the performance and conversion efficiency of LED power supplies of different specifications are different, choosing a suitable and efficient LED power supply can truly show the high-efficiency characteristics of LED light sources. Because the low-efficiency LED power supply itself consumes a lot of electricity, the energy-saving characteristics of LED cannot be highlighted in the process of powering the LED. In short, the stability, energy saving and life of LED power supply in LED work play an important role.