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Constant Power Design of LED Driver

Jun 12, 2019

Meanwell Driver:Constant Power Design of LED Driver

 

Recently, one of the most popular topics in the LED power industry is the constant power drive of LED. Why do LEDs have to be driven by constant current? Why can't they be driven by constant power? Before discussing this issue, we must first understand why LED must be driven by constant current. As illustrated by the graph LED curve, when the forward voltage of LED changes by 2.5%, the current through LED will change by about 16%, and the forward voltage of LED is easily affected by temperature. The temperature difference between high and low temperatures will even cause electricity. The voltage difference is over 20%. In addition, the brightness of the LED is proportional to the forward current of the LED. Excessive current difference will lead to excessive brightness change, so the LED must be driven by constant current. However, can constant power drive be used for LED? Firstly, the issue of whether constant power is equal to constant brightness is discussed. From the point of view of simply discussing the design of constant power driver, the change of LED and temperature curve seems feasible. Why doesn't the manufacturer of the LED driver directly design the constant power driver? There are many reasons involved. It's not difficult to design the constant power circuit. It's so convenient to use MCU (Micro Controller Unit) to detect the output voltage and current, to control the responsibility period of the PWM (Pulse Width Modulation) through program calculation, and to control the output power on the blue constant power curve of figure. Constant power output can be achieved, but this method increases a lot of costs, and when the short circuit damage occurs, the constant power LED driver will increase the current because of the detection of lower voltage, which may cause greater harm. In addition, the temperature characteristic of LED is negative temperature coefficient. When the temperature is higher, we expect to reduce the output current to maintain the performance of long life of LED. However, the constant power method is inconsistent with this consideration. In high temperature application of LED, the output current of LED driver is increased because of the detection of low voltage. Considering all the above factors, it is the most effective solution to provide customers with "quasi-constant power" LED driver with wide range voltage/current output.

 

The constant power LED driver labeled by some products of Meanwell uses this kind of constant power optimization design specially. The purpose is to provide customers with a wide range of voltage/current output quasi-constant power LED driver. It can not only take into account the needs of users and avoid the cost increase caused by over-design or the trouble caused by the characteristics of LED, but also cause lamp failure and provide quasi-constant. Wide-range design of power products can be said to be the most effective solution of LED driving power supply on the market at present.