One of the hottest topics in the recent LED power supply industry is led constant power drive. Why must LEDs be driven by constant current? Why can’t constant power drive?

Before discussing this topic, we must first understand why LEDs must be driven by constant current?

As illustrated by the LED I-V curve in figure (a), when the forward voltage of the LED changes by 2.5%, the current passing through the LED will change by about 16%, and the forward voltage of the LED is easily affected by the temperature. The temperature difference between high and low temperatures will even make the voltage change gap as high as more than 20%. In addition, the brightness of the LED is directly proportional to the forward current of the LED, and the excessive current difference will cause excessive brightness change, Therefore, the LED must be driven by constant current.

However, can LEDs be driven by constant power? First of all, excluding the issue of whether constant power is equal to constant brightness, it seems feasible to simply discuss the design of constant power driver from the perspective of the change of LED I-V and temperature curve. Then why don’t LED driver manufacturers directly design LED drivers with constant power drive? There are many reasons involved. It is not difficult to design a constant power line. As long as it is combined with MCU (micro controller unit) to detect the output voltage and current, control the PWM (pulse width modulation) responsibility cycle through program calculation, and control the output power on the blue constant power curve in figure (b), the constant power output can be achieved, but this method increases a lot of costs, Moreover, in case of LED short-circuit damage, the constant power LED driver will increase the current because of detecting a lower voltage, which may cause greater harm. In addition, the LED temperature characteristic is a negative temperature coefficient. When the temperature is higher, we expect to reduce the output current to maintain the high life performance of the LED. However, the constant power approach conflicts with this consideration. In LED high-temperature applications, the LED driver increases the output current because it detects a lower voltage.

Considering the above factors, the “quasi constant power” LED driver that provides customers with a wide range of voltage / current output is the most cost-effective solution for customers. The constant power LED driver marked by some products of Mingwei adopts the optimized design of this kind of constant power, which aims to provide customers with a wide range of voltage / current output. It can not only meet the needs of users, but also avoid the cost increase caused by over design or the trouble caused by LED characteristics, and even cause lamp failure, Providing a wide range of design products with similar constant power can be said to be the most effective solution for LED driving power supply on the market.