One of the hottest topics in the LED power supply industry recently is non-LED constant power driving. Why LED must be driven with constant current? Why can't it be driven with constant power? Before discussing this topic, we must first understand why LED must be driven with constant current? When the LED forward voltage changes by 2.5%, the current through the LED will be approximately 16% change, and the LED forward voltage is easily affected by temperature. The temperature difference between high and low temperature can even make the voltage change more than 20%. In addition, the LED brightness is proportional to the LED forward current, and the current difference will cause the brightness to change too much. Large, so the LED must be driven by a constant current.

However, can LEDs be driven with constant power? First of all, the issue of whether constant power is equal to constant brightness is eliminated. From the perspective of simply discussing the design of constant power drivers, the changes in the LED I-V vs. temperature curve seem feasible. Then why don’t LED driver manufacturers directly design constant power LED drivers? There are many reasons involved. It is not difficult to design a constant power circuit, as long as it is matched with an MCU (Micro Controller Unit) to detect the output voltage and current, and calculate it through the program. Control the PWM (Pulse Width Modulation) duty cycle and control the output power on the blue constant power curve in Figure (b), so that constant power output can be achieved, but this method adds a lot of cost, and when LED short-circuit damage occurs, constant power output The power LED driver will increase the current due to the detection of a lower voltage, and this phenomenon 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 performance of the LED's long life. However, the constant power method contradicts this consideration. When the LED is used at high temperature, the LED The driver has increased the output current because it detects a lower voltage. Considering all the factors mentioned above, the "constant power" LED driver that provides customers with a wide range of voltage/current output is the most effective solution for customers.