LED display screen has many electronic components, complicated circuit, large number of LED lamps, and high reliability, which will directly affect the actual use value of the display. Therefore, when designing the LED display screen, we all hope that the designed display can achieve high reliability, good working stability and long service life. Therefore, after the performance indicators and cost requirements of the display screen are put forward, it is necessary to analyze the performance and reliability of the components used in each module of the system before the development and production, and to carry out the final stability state of the entire LED display. Estimate the calculation and analyze the unit with higher failure rate in the designed display, so that it can be improved by selecting better performance components, replacing components, applying redundant systems, strictly controlling the manufacturing process and strictly controlling the inspection. Small failure rate, focus on the weakest link.
In addition, reliability analysis can help us to compare various design solutions, find the design that maximizes the system reliability index, and provide the basis for the selection of components, parts and materials at design time. Provide information for review, failure analysis, maintenance analysis, and thermal design. This article uses the component counting method, taking an outdoor LED display box as an example to introduce how to predict the reliability of the display, and analyzes the key factors affecting the reliability of the display and proposes ways to improve the reliability.
1. Reliability prediction method
1.1 Product life cycle
From the perspective of reliability engineering, the product life cycle is roughly divided into three stages: early failure period, normal use period and wear aging failure period. The relationship between failure rate and time at each stage follows the bathtub curve, as shown in Figure 1.
Early failure period: Due to defects in the design, manufacturing, materials and other processes, the failure rate is high when the product is first used. The higher the level of enterprise quality management, the shorter the process.
Normal use period: The failure of the product during this period is related to the product quality and the use environment. It is randomly occurring. The better the quality, the low failure rate and almost constant, so the usable life is longer.
Loss of energy: As the life of each major component of the product has reached, various faults “accumulateâ€.
1.2 Failure rate
Failure rate is the cumulative number of irreparable failures of a product at a given time interval, defined as λ.
1.3 Reliability
Reliability refers to the ability of a product or system to perform a specified function within a specified time under specified conditions. The usual way to express reliability is MTBF, which is the average time between failures of the product. The average time between failures is calculated by dividing the total running time by the number of product failures.
When the electronic product enters the normal use period, since the failure rate is almost constant, the reciprocal of the failure rate λ is generally used to represent the MTBF value to measure the quality level of the product:
1.4 Reliability prediction method
Reliability estimation methods generally include component counting method, similar product method, similar circuit method, active device method, scoring prediction method and component stress analysis method. This paper uses component counting method to predict the reliability of LED display. The so-called component counting method is a method for predicting equipment failure rate based on the general failure rate of various components constituting the device and the number of uses thereof. Applicable to the electronic equipment program demonstration stage and preliminary design stage, the types and quantities of components have been roughly determined, but when the specific work profit and environment are not clear, the basic reliability of the system is predicted, and the basic principle is also for the components. Correction of basic failure rate. The calculation step is: first calculate the number of various types and various types of components in the device, and then multiply the basic failure rate of the corresponding model or response type component, and finally add up the multiplication and accumulation to obtain the product failure. rate. The calculation formula is:
2. Reliability prediction of LED display box
The projected display box in this paper is a series model. The units including redundant or alternative working modes are processed in series, and then the component counting method is used to predict the failure rate of the model, and then the MTBF time is solved.
The display box to be estimated is composed of six 300W power supplies, one receiving board, one adapter board and 24 lights. The display features: full color screen, design brightness 8000cd/m2 The pixel pitch is 16mm, and the constant current drive is 1/8 scan.
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