The characteristics that the led display power supply needs to have

The characteristics that the LED display power supply needs to have

 

 

 

 

What kind of functions should the power supply of outdoor LED display have to meet the demanding power supply needs of LED display?

 

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

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 changes in outdoor light, according to different climates and time periods, the voltage value corresponding to the brightness of the full-color screen is tabulated in advance and stored in the single-chip microcomputer. Check the meter according to the signal sent by the light sensor, and obtain the output voltage value of the CNC switching power supply to control the brightness of the display screen.

 

Compensate for the change in the forward voltage drop VF of the LED caused by the ambient temperatureThe positive voltage drop VF of the LED decreases as the ambient temperature rises. The coefficient of temperature change varies from LED to LED. Over the normal operating temperature range, the VF can vary by up to 20%. Driven by constant voltage, a decrease in VF causes the LED current to rise, causing the overall temperature to rise. In this feedback process, the working condition of LED will deteriorate more and more, which will seriously affect the quality and life of outdoor screens. Therefore, the switching power supply of the outdoor screen is required to have a 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 enter a negative temperature coefficient thermal electrocathode with a 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 drops and the output voltage drops, suppressing the rise of the LED operating current. Due to the high discrete nature of thermistors, it is necessary to select them to ensure product consistency. In addition, there is an independent resistance combination for each temperature change rate, and the interchangeability is poor. In order to overcome these shortcomings, a numerically controlled switching power supply with an output controlled by a digital signal is adopted. According to the temperature drift curve of various LEDs, the driving voltages that need to be supplied to LEDs at different temperatures are tabulated and stored in the single-chip microcomputer for inquiry. According to the temperature table measured by the temperature sensor microcomputer, the output voltage of the corresponding CNC switching power supply can be obtained.