LED driver constant voltage and constant current comparison

The constant current power supply method is an ideal LED power supply method. It can avoid current fluctuations caused by changes in the LED forward voltage. At the same time, the constant current makes the brightness of the LED stable. Therefore, generally advanced LED circuits use constant current to drive LEDs.

The circuit diagram below is a low-cost, high-performance LED constant current power supply circuit designed by Electronic Production Network;

When we design LED driver power supply, we must know the LED current and voltage characteristics. Due to different LED manufacturers and LED specifications, the current and voltage characteristics are different. Taking the typical specifications of white light LED as an example, according to the current and voltage change law of LED, the applied forward voltage is about 3.0-3.6V, the typical value voltage is 3.3V and the current is 20mA. According to the current and voltage in the circuit diagram, I=2.5V/120=20mA; V=(3.3+3.3)/0.7=9.5v is calculated; because the circuit constant current accuracy is very high, V can be taken as 10V-12V, and the circuit will automatically stabilize the current and voltage at normal values. If the forward voltage applied to both ends of the LED exceeds 3.6V, the forward voltage increases very little, but the forward current of the LED may increase exponentially, causing the temperature of the LED light source to rise, 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 change characteristics of the LED, strict requirements are put forward for the design of the LED power supply. Designer: Mr. Lao Duo believes that although LED is more efficient than ordinary light sources in terms of energy saving, LED light sources cannot directly use 220 grid voltage like ordinary light sources. It must be equipped with a dedicated power supply. Only by providing a dedicated LED power supply that can meet the rated voltage and current of LED can the LED operate within the normal working range. However, since the performance and conversion efficiency of LED power supplies of various specifications are different, choosing a suitable and efficient dedicated LED power supply can truly reveal the high-efficiency characteristics of LED light sources. Since the low-efficiency LED power supply itself consumes a lot of electricity, the energy-saving characteristics of LED cannot be displayed in the process of powering the LED. In short, LED power supply plays an important role in the stability, energy saving and life of LED work. Due to its many advantages such as environmental protection, long life and high photoelectric efficiency, LED has been rapidly developed in various industries in recent years, and LED power supply has become a hot topic. Theoretically, the service life of LED is more than 100,000 hours, but in actual applications, due to improper selection of the design of the driving power supply, the LED light decay is accelerated, the life is shortened, or even damaged. Many manufacturers produce LED lighting products that use RC voltage reduction and a voltage regulator diode to power the LED. This method of driving LEDs has defects, mainly because of low efficiency, which consumes a lot of power on the voltage reduction resistor, and may even exceed the power consumed by the LED, and cannot provide high current drive, because the larger the current, the more power consumed on the voltage reduction 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 poor ability to stabilize the voltage cannot ensure that the current passing through the LED does not exceed its normal working value. When designing products, the voltage at both ends of the LED is reduced to power the drive, which is at the cost of reducing the brightness of the LED. The brightness of the LED driven by the RC voltage reduction method 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 by the RC voltage reduction 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. There is another LED driving method that is feasible. It is neither constant voltage nor constant current, but through the design of the circuit, when the forward voltage of the LED increases, the driving current is reduced, ensuring the safety of the LED product. Of course, the increase in forward voltage can only be within the range that the LED can bear, and too high will also damage the LED. The ideal LED driving method is to use constant voltage and constant current, but the cost of the driver increases. In fact, each driving method has advantages and disadvantages. According to the requirements and application scenarios of LED products, it is key to reasonably select the LED power supply method and accurately design the power supply.