Ten Misunderstandings Often Faced by Hardware Engineers When Designing Circuit Stability

There is not only a lot of circuit design skill, but also a lot of misunderstandings. In this article, we will introduce you to ten misunderstandings related to circuit stability design.

Myth 1: Product failure = product unreliable

Sometimes, problem of product is not a research and development problem. There have been cases where equipment for middle and highly developed regions of China has been exported to Colombia because it has been well used in China, but there have been frequent failures. The reason for failure is that height above sea ​​level in developed areas of mainland China is relatively small, so tightness of equipment in high mountain areas is questioned, and leakage rate increases as pressure difference between inside and outside of equipment increases.

When project was approved, only low altitude was taken into account, so there were no problems with their design. Your boss asked for this. Whoever decides to export this model to Colombia is to blame. If an R&D boss is involved, He is simply biggest sinner for making decisions without objection. After all, sales managers can be forgiven for making decisions without understanding technology, and mistakes of a technical vice president are incompetent.

Product reliability is "the ability to perform a given function for a given time and under given conditions." Readers should carefully study this definition, study things to find out, and see who can gain more knowledge when they can fit this definition. The conditions in area of ​​use often exceed specified conditions, and this excess may be implicit.

Myth 2: transition process = steady state process

The introduction to "Curve Affecting Product Reliability and Social Harmony" is a good illustration of content of this graph.

Myth 3: Downgrading is easy, it's not a problem

Everyone can derank how to draw, everyone can, but not everyone can survive by drawing. See article "Derating of Electronic Products" for details. Here is just a summary:

1. Devices with same functions but different processes have different derating factors;

2. Derating factors for adjustable and fixed value devices are different;

3. Different loads have different derating factors;

4. The derating factors for wires of same specification are different in multi-turn and single-turn applications;

5. Some parameters cannot be lowered;

6. A derating of junction temperature cannot be ruled out.

Misunderstanding 4. That device can be used with confidence

Why is device damage often referred to as "fire"? The reason is that most device failures are due to overheating. Pay attention to two points. First, ambient temperature of device ≠ ambient temperature of whole machine, and environment of device is affected by other devices in chassis Due to effect of heat dissipation, ambient temperature of main unit is higher than ambient temperature of whole machine.

ErrorZone 5: Reliability of electronics has nothing to do with mechanical and software knowledge

Installation, wiring, layout and spraying affect electrical performance; electromagnetic compatibility, virtual welding, heat dissipation, vibration and noise, corrosion and grounding are related to structure; software error prevention, error evaluation, error correction and error handling measures. Mechanical and electronic defect problems can be avoided.

Misunderstanding 6: The device is very simple, it doesn't matter if there is a datasheet

When designing, you must get Datasheet of all devices, then read all graphs, diagrams and parameters on it, and finally relate to these curves in design. The figure below shows volt-amThe first characteristic of diode. When designing, it is necessary to carefully confirm static operating point of device in our circuit.

Myth 7: Maintainability has nothing to do with me

What is purpose of working on reliability of electronics? To make money. What do you rely on to make money? Open source and cost reduction. It's hard to increase income and easy to cut costs. Do not always think about saving on material costs. Material costs are saved and maintenance costs are high. dying early, you will die sooner or later. Why bother?? It is better to die early and be born early. It is best to pay attention to maintainability and save on this part of cost. This is real profit.

Misconception 8: If process control is bad, there are no good masters

Poor process control is not only a problem for craftsmen, but also process of building a value chain. The design engineer's requirements for device, selection of manufacturer by purchasing engineer, and control content of inspection link should be developed for key indicators of device. The detection method should not represent mechanism of component failure and damage, and assembly link should not lead to damage oven, anti-static treatment of manual soldering table, etc.), factory inspection link should check drift part of device parameters, which may lead to product failure, and maintenance link should not present a failure.

It can be seen from above that in event of a problem, two process engineers can guarantee it. Therefore, it is concluded that a special approach is to ensure consistency. The prerequisite for consistency is that designer provides sufficient technical information as a matter of priority, and process is based only on design drawings and design documentation to ensure that production reliability is infinitely close to design reliability.

Misconception 9: The relationship between MTBF value and failure rate of one particular machine

MTBF is a macroscopic and statistical concept, while single device failure is a microscopic and concrete concept. Customers love to ask question, “Your product has an MTBF of 10,000 hours, so if I buy yours, will there be any issues within 10,000 hours?” 1 km or 1 kg?

Myth 10. Reliability problems can be fixed with more testing

Because this question can be classified as one of ten most popular myths, its definition is, of course, incorrect. There are three summaries:

1. Some problems cannot be detected by simulation tests;

2. Test method = engineering calculation, specification check, simulation test, electronic simulation;

3. Corresponding working time at low temperaturetemperature cannot be calculated from results of heat resistance test.