Technology – Characteristics of LED display power supply

What functions should the power supply of outdoor LED display have to meet the demanding power supply needs of LED display? Below we have collected some professional LED display power features.

Under certain conditions, keep the LED pixels driven by constant current. The change of LED group voltage caused by the change of display load will affect the pixel current and cause the change of brightness. In order to ensure the brightness uniformity of the whole screen module and reduce the brightness change, move the sampling point of the switching power supply output sampling circuit from the power port to a point in the display screen to keep the voltage at that point unchanged. The electrification of load change is adjusted by switching power supply, that is, when the load is small, the output voltage is low, and when the load is large, the output voltage is high. Therefore, under the condition of constant temperature and brightness, the voltage output to the LED module is constant and the pixel driving current is constant.

The brightness of the display screen is controlled by adjusting the voltage of the switching power supply. In order to make full use of the limited resources in the full-color screen control system, the switching power supply is required to adjust the brightness of the full-color screen by adjusting the output voltage. Due to the large change of outdoor light, the voltage value corresponding to the brightness of the full-color screen should be made into a table in advance and stored in the single chip microcomputer according to different climate and time periods. Check the table according to the signal sent by the light sensor to obtain the output voltage value of the NC switching power supply to control the brightness of the display screen.

Compensate for the change of led forward voltage drop VF caused by ambient temperature. The forward voltage drop VF of LED decreases with the increase of ambient temperature. The temperature variation coefficients of various LEDs are different. Within the normal operating temperature range, the change of VF can reach 20%. Under constant voltage drive, the decrease of VF will lead to the rise of LED current and the rise of overall temperature. In this feedback process, the working condition of LED will be worse and worse, which will seriously affect the quality and service life of outdoor screen. Therefore, the switching power supply of outdoor panel is required to have temperature compensation function to ensure that the LED driving current does not rise with the increase of temperature.

The simple temperature compensation method is to connect the negative temperature coefficient thermal cathode with the temperature change rate close to ledvf in the switching power supply, and introduce the switching power supply PWM chip to compare the reference voltage Vi (VO = kvi). When the temperature rises, VI decreases and the output voltage decreases, which suppresses the rise of LED working current. Due to the large discreteness of thermistors, they need to be selected in order to ensure the consistency of products. In addition, the interchangeability of each combination is different from that of the other. In order to overcome these shortcomings, the NC switching power supply whose output is controlled by digital signal is adopted. According to the temperature drift curves of various LEDs, the driving voltage to be provided to LEDs at different temperatures is made into a table and stored in the single chip microcomputer for query. According to the temperature measured by the temperature sensor single chip microcomputer, the output voltage of the corresponding NC switching power supply can be obtained.