Design and Analysis of Constant Current Drive Circuit for LED Display

1 Introduction

LED display screen is a new type of information display media that has been rapidly developed around the world in the late 1980s. It uses a dot matrix module or pixel unit composed of light-emitting diodes to form a large-area display screen with high reliability, long service life and strong environmental adaptability. It has high performance and price ratio and low cost of use. It has been widely used in the field of information display.

The LED display mainly includes an array of LEDs, a driving circuit, a control system and a transmission interface, and corresponding application software, among which the design of the driving circuit is good or bad, and the display effect, manufacturing cost and operating performance of the LED display are A very important role. Therefore, it is necessary to design a control drive circuit that satisfies the requirements of the control drive while using fewer devices and lower cost. This paper analyzes the design of the conventional drive circuit and proposes the design of the constant current drive circuit.

2, LED display conventional drive circuit design

The design of the LED display driver circuit, in conjunction with the control system used, is generally divided into dynamic scanning type driving and static latch type driving. The following is an example of the design of the dynamic scanning type driving circuit for analysis:

The dynamic scanning type driving method refers to the four rows, eight rows, 16 rows and the like, and the n rows of light emitting diodes share a set of column driving registers, and the time sharing operation of the row driving tubes makes the lighting time of each row of LEDs total. 1/n of time, as long as the refresh rate of each line is greater than 50 Hz, people can see a complete text or picture by using the visual persistence effect of the human eye.

Conventional driver circuits are generally designed with a serial-integrated integrated circuit chip such as the 74HC595 or MC14094 as a column data latch, a small power N PN transistor such as 8050, and a Darlington triode TIP127. The line scan tube has a circuit as shown in Figure 1.

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