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The PSU is one of the most important parts in the PC. But how is a PSU constructed and then built?

The PSU is one of the most important parts in the PC. If there are malfunctions, it can cause disturbances and damage or even destroy the whole hardware in the worst case. Inferior PSU’s sometimes don’t comply to the ATX-Specifications, formulated by Intel, and cause an unstable System. We want to show you how to develop and produce a good PSU by looking at COUGAR-PSU’s by HEC/Compucase. In the beginning there is the development. The ATX-Specifications by Intel play a big role in ensuring the biggest compatibility. Some other aspects have to be clarified in the beginning, for example for which use the PSU’s are going to be. There are huge differences between Industry-PSU’s and those used in Gaming-PC’s, so a preselection is defined clearly. The use of COUGAR-PSU’s is claerly defined. They are for private users with higher standards, even suitable for Multi-GPU- and Multi-CPU-Systems and have to fit their special demands. Often we hear about the “new” DC-DC-Technology, in which the 3,3- and 5-Volt-Voltages are built out of the 12-Volt-Rail – this increases the efficiency and stability.

This technology exists since more than ten years, but was too expensive, to use them in PSU’s for private use. The technology is still a bit expensive, but it has it’s benefits in using it in PC’s with a very high need of energy, and by comparing it to other components it is not that much expensive. The decision, if a PSU shall be built with the “classic” design or with DC-DC-Technology, has to be clarified in the beginning, because the basic layout decides of all following steps. After working this out , the next step follows. Now the cooling-concept has to be fixed, whether it should be the classic variant with a 80-mm-fan, placed at the back, or choosing a vertical cooling with a 120- to 140-mm-fan. This point is very important, to develop the actual layout, which has to be customised. Using present PSU’s and changing the cooling-concept is not advisable. For example COUGAR-PSU’s are cooled vertically (Power-Series 120mm and CM-Series 140mm), because of that the cooling is produced in a fitting way and in this special case as small as possible, so that the airflow is not influenced in a negative way.

Choosing the components

Now the real choosing of the components begins. We know the Requirement-profile, the basic layout and the cooling-concept. Very much electronic components are required for building a PSU. The most important ones are the condensers for the primary (input) and secondary (output) side, several transformers, different coils, of course the board, mosfets, the fan and a chip for

security-functions. Parallel to that the PSU is being designed on the PC. The housing for a PSU is a self-made product from COUGAR and is being cut out of steel, grinded, polished and lacked. The requirement for a PSU is a very good quality, so that no wishes rest. The components are picked only, if they fit to that. So COUGAR only uses high-performance parts. But it is not enough just to choose the best components and stick them together. The individual parts have to match together perfectly. Here it may come to incompatibilities. Also the finished PSU has to correspond to the actual security-standards and has to be in accordance with the the Electro-Magnetical-Interferience (EMI) of the EU-norms, which are often ignored by cheap PSU’s. This aspect has to be checked meticulous. Experienced manufacturer can look back on many years of knowledge and their own “know-how” , to realise and prevent possible problems before starting.

Order of the components

The order of the components on the board has to be suitable for the actual production. If components let themselves be integrated difficult and time-wasting, this has some handicaps. A complicated assembling includes a higher probability of

mistakes in processing. A high use of time is a problem in the assembly line; if the production stops in one place, the whole product gets more expensive because of the delay. A good example for the time of developing is the COUGAR-Series, which was about six month, checking every detail. After finishing the board-layout and choosing all components, it comes to a so-called “pilot-production”. In this production, 20 to 50 PSU’s are produced on different days. During this “Mini-production” special attention is paid on the single steps of production. Delays in the practical production are faced and optimised afterwards. After that the manufactured PSU’s are getting proved very intensively. After that the important test of EMI (Electro-Magnetical-Interferience) follows. There are several regulations, which declare exact values, which may not be passed. A good EMI-test is about a hundred sites.

Following tests

Also, an actual test of function is getting performed. Parameters like the stability of voltage, performance results, temperature results or the noise are tested in different conditions and configurations. If this test is successful, the security test is rendered. This includes not only the internal functions, like OVP (Overvoltage protection), but also tests on single components. For example no single components may be overloaded out of their specification in an extreme way. Even in an extreme case, no parts may explode and endanger humans or the machine. Therefore the EU-norm EN 60950 exists, in which also the stability on fire of the board is regulated, so that they don’t mutate into a fire, even if there are high temperatures. At last the PSU’s are strained on 110 percent in a cage with temperatures of about 50 degree Celsius for a few hours.

This test is surely the hardest for the PSU, because with this conditions the PSU’s will not be pursued later on. When this last test is finished, we begin to plan the mass-production. Normally, the tests aren’t fulfilled completely in the first session. Also there are many differences between theory and praxis in the production of PSU’s. While testing the PSU’s often things to be optimised are found, not only at the product, but also in the production-line. That’s another point in choosing components: They have to be available all time, even in big amount. A short-term change in choosing parts can have bad consequences. When these optimisings are finished. it comes to another test-production. This time an amount of more than 100 pieces is produced. Doing this shall confirm the results of optimising. After that the real production begins.

PSU-production

As mentioned before, cases for the PSU’s are produced separately and join the way of production as a finished product. Before the single components can be mounted, the board has to go through the so-called “SMD-Machine”. It equips the board with tiny components, which are too small for mounting it by hand. Additionally the full-automatic machine saves time and money. When the board, also called “PCB”, is finished, the real production of the ready product begins. The PCB is laid on the beginning of the assembly line. Now it goes through different stations, on which each time one component is put on the right

place by hand. Parallel to that the integrated components for the circuits are getting screwed and isolated, like Mosfets with the cooling-trunk. After that the finished packet is put on the PCB. When all components, including the cooling-trunk, are all put in the right place, the input is put in its place, too. It is that part, which will combine the cold-device-socket with the PCB later on, the interface between the socket and the origin PSU. In the end the cables are getting solded. In the COUGAR-PSU’s are additionally isolating shrinkage tubes used, which give an extra isolation to the output of the PCB. After that the ready equipped board is going to the solding-machine. This machine solds the already prepared components to the PCB. Since a few years there is a EU-norm , which is known as RoHS. It says, that the finished product may not contain poisonous materials in higher concentrations. Especially in processes of solding, some time ago often materials were used, which contained lead and are not allowed today.

Last steps

Now the board is nearly finished. After the solding, overlaying contact feet of the components have to be deleted, which is done by another machine. After that the finished PCB’s get over a scanner. This proves full-automatically, if the solding-points are correct to 100 per cent. Before the production begins, the exact layout of the actual produced PSU-series is sent to the computer. Because of that the machine knows exactly, where things got solded and can check it correctly.

In productions with a high-quality-standard, like the COUGAR-series, the PSU’s are checked again, by schooled workers, which look for the quality of the solding after the machine-check. The basic-PSU is now ready, only the case and the fan are left to be mounted. After that the “naked” PSU is getting a basic-function-test. In this test the input and especially the output lanes are proved. If the test is positive, the PCB, including the cables, is put into the case and gets mounted, together with the fan. Now, before the PSU gets its sticker and gets packed completely, another big and detailed test waits for the PSU. In this one, all tests from A to Z are made again: input-voltage, output-voltages, performance values, maximum loads of single lanes, safety functions in the PSU, dynamic load distribution function, the function of the fan, the control of the fan and again the EMI-test, which includes the surge-test. If this marathon is absolved positive, comes another – you surely know – test.

Burn-in-test

In the so-called Burn-in-test, the PSU is getting highly loaded under extreme conditions. In this test, we don’t simulate durable an exactly same load, but a permanently changing load. Sometimes there are higher loads on the 3,3- or on the 5-V-lane, and sometimes an extreme load on the 12-V-lanes. To that comes a sudden reduction of the full-load onto 10 per cent, just to raise it up to 110 per cent a few seconds later. After that test, the PSU’s are brought into a special room, to cool down on some racks, just to pack them in the final step. After the PSU finished all of those tests positively, it gets a serial-number. This number is getting archived, to look back on dates of producing each PSU.