Publisher: Supplier of LED Display Time: 2022-10-12 18:26 Views: 145
With the development speed of the industry LED display, the full-color LED display also puts forward higher requirements for the line drive, and the display quality of the LED full-color display has always been closely related to the input voltage. From simple P-MOSFET to achieve line switching, to more integrated and more functional multi-function line driver. The display quality of the LED display has always been closely related to the input voltage. So what faults will occur when the voltage of the color led display is unstable? Next, the editor of LCF will give you a detailed introduction.
When the LED is short-circuited, there will be a long-bright phenomenon, which is generally called a short-circuit caterpillar. When the middle LED lamp bead is short-circuited, if the voltage difference between VLED and point A is greater than the lighting value of the LED lamp bead, a column of constant voltage will be formed, which is a bright caterpillar. The difference between the short-circuit caterpillar and the open-circuit cross is that the short-circuit caterpillar will appear as long as the screen is in the scanning state, regardless of whether the LED lamp beads display an image or not.
2. Lamp reverse voltage
The reverse impulse voltage of the lamp beads greatly affects the service life of the lamp beads, and the dead pixels caused by the back pressure have always been the pain point of the LED full-color display, especially the small spacing. When the output channel is closed, due to the freewheeling effect of the parasitic inductance, the parasitic capacitance at the channel will continue to be charged, forming a high voltage glitch. At this time, a reverse voltage loaded on the lamp bead is formed with the output of the line tube, so the blanking voltage of the line tube affects the reverse voltage of the lamp bead at the same time. When the voltage at the constant current output channel is fixed, the higher the blanking voltage of the line tube, the smaller the reverse voltage of the lamp bead.
In fact, after testing by LCF LED display manufacturers, the reverse voltage below 1.4V can greatly reduce the dead pixels caused by reverse voltage. Therefore, for the lamp reverse voltage problem, the blanking voltage should not be too low. Generally not lower than VCC-2V.
3. Open Cross
In the scanning screen, when the lamp bead is open and the point is lit, the voltage of channel OUT1 is pulled down to below 0.5V. If the scanning line potential blanking voltage VH is 3.5V, a conduction path will be formed for the column of lamp beads, forming an open-circuit caterpillar. When the lamp bead is open, the voltage of the channel OUT1 is pulled down to below 0.5V or even 0V, and the parasitic capacitance Cr of the column is affected by the parasitic capacitances C1 and C2. When the potential of Cr is pulled down, the LED in the same row as the open lamp bead appears. Hidden bright. Hidden bright. The problem of split ends can be solved by reducing the blanking voltage of the blanking line, that is, the blanking voltage VH.
4. On the ghost
When the scanning screen is switched, since it takes a period of time for the PMOS switch to be turned on and off and the discharge of the charge on the parasitic capacitance Cr of the row line, the unreleased charge of the VLED of the previous row scan is conduction path. When turned on, the row parasitic capacitance Cr is charged to the VCC potential. When switching to Row(n+1), a potential difference is formed between Cr and OUT, and the charge is discharged through the lamp bead, resulting in a dim LED. Therefore, it is necessary to discharge the charge on Cr in advance at the time of line feed. Usually, the line tube with integrated blanking function can quickly discharge the charge of the parasitic capacitor Cr when switching is performed by adding a pull-down circuit. The lower the pull-down potential, that is, the blanking voltage VH is set, the faster the charge on the parasitic capacitor discharges, and the better the effect of eliminating ghosting. Usually, VH<VCC-1V can eliminate ghosting.
The above are the faults that will occur when the voltage of the color LED display is unstable, and I hope it will be helpful to you. At the same time, you are welcome to correct or add. LCF is a world-leading provider of LED display applications and solutions, as well as a national-level specialized, special, and new little giant enterprise. The main business covers "smart city", "cultural tourism business performance", "commercial display project", "content technology" four major sections, with the world's leading automated production equipment and modern post-doctoral research laboratory and perfect sales and services team. Friends who want to buy LED display can also contact us, LCF LED display manufacturer, a big country brand, trustworthy!