The power supply is the heart of the electronic system. In industrial applications, the power supply for the system's preamplifier or interface generally requires high anti-interference performance. Various isolated module power supply modules have emerged. You may know the design of isolated power supply, but can you really design a stable power supply? This article reveals secrets for you.
First, why the power module needs to be isolated
1, protect personnel from physical and electrical damage
The isolation voltage of the power supply is also known as the electrical strength in GB-4943 GB. This GB-4943 standard is the safety standard for information equipment that we often say. It is a national standard to prevent people from physical and electrical harm, including avoiding People receive electric shock injuries, physical injuries, explosions, and other injuries. Figure 1 shows the isolated power supply structure as shown below. In particular, the DC DC-DC module power supply that exceeds the human body safety voltage at the previous stage, such as the 137.5VDC railroad module power supply, and the 1200VDC power module product for photovoltaic applications, may not be physically isolated and may cause physical and electrical damage. In the medical industry, the requirements for isolation of the power supply are higher. Generally, it is required to strengthen the insulation isolation. The higher the isolation, the smaller the leakage current, and the leakage current of a few milliamps can take a patient's life.
Figure 1 GB-4943 standard
2. Protection of post-load devices and systems
Isolated power supply input and output isolation, in the event of an abnormal power supply products, can protect the role of the rear load equipment and systems to avoid the risk of electric shock, physical injury, explosion and other injuries. It is common to see power products that are damaged by lightning surges and transient high-voltage surges. A large area of ​​components on the circuit board is blown away and carbonized. In fact, many devices are directly harmed by high voltage and pressure and crosstalk and radiation to avoid high voltage and pressure. The isolation plays a very good role in the damage of the lower level weak electricity.
Figure 2 rear stage load damage
3, improve the common-mode interference suppression performance and anti-interference ability
Isolated power supply removes the ground loop between isolation circuits, which can cut off the propagation path of common mode, surge and other interference signals, effectively reduce the influence of ground potential difference and wire coupling interference, and can improve common mode interference suppression performance and anti-interference ability. The use of advanced systems that are more sensitive to interference signals and their integration, such as instrumentation, data acquisition devices, and embedded systems, have become more and more widely used in remote industrial communications. For power supply, the isolated power supply is generally used to provide power for each communication node. At the same time, it also has higher safety and reliability, especially the EMC characteristics of conduction disturbances, radiation disturbances and ESD electrostatic discharge and other performance is also better, and in the system can easily complete the output wiring, but not with the main ground conflict.
Figure 3 Instrumentation
Second, how to achieve power isolation
Currently, there are two main power isolation schemes in the industry: one is to use a transformer magnetic isolation + optocoupler photoelectric isolation combination to achieve electrical isolation between the primary side and the secondary side. In this way, the circuit is simple and mature, easy to implement, and can achieve high output voltage accuracy, linear adjustment rate and load regulation performance to meet the high performance requirements of current electronic products.
Figure 4 Optocoupler isolation scheme
The other is a transformer-only magnetic isolation scheme. This kind of transformer magnetic isolation primary feedback sampling method has a higher requirement for the consistency of the transformer, and the output voltage accuracy, linear adjustment rate and load regulation performance are relatively poor. In fact, some people in the industry have also studied the use of piezoelectric ceramic isolation, new technology, performance is difficult to achieve the previous two methods, and equipment and equipment investment costs are very high, basically no further research and promotion.
Figure 5 primary side feedback sampling scheme
Third, self-built VS module solution
At present, when some engineers design products, the choice of power supply scheme has such an idea. It will be considered that for several materials, the material models are known, and their unit prices are known. The price of the power supply module is relative to the cost of the material. It seems to be more expensive. This part of the user wants to build it by means of discrete devices. Let me explain from a few points to you, why choose to purchase power supply module products.
1, program options
After the product performance requirement is slightly clearer, the next step is to start design and development. The first thing to do is to select the circuit scheme. The following is a list of some of the more common "negative materials."
For example, the design and development of a commercial AC input to DC output, many people think of the first time the use of frequency conversion circuit program, because this program is relatively simple, an industrial frequency transformer, coupled with a rectifier filter can handle, as follows Figure 6 shows. The efficiency of the products using this solution is very low, and the volume of the products will be very large, and in the application is also accompanied by a very disturbing power frequency vortex sound. The appropriate transformer is selected for the module scheme, and multiple process layers ensure the product consistency of the transformer and ensure the final product performance.
Figure 6 Comparison of transformer solutions
2, material selection and PCB design
After the circuit scheme is determined, the design of the product performance parameters needs to be performed next. The electronic component design and calculation in the circuit scheme and the structural material selection must be weighed in various aspects.
First, the selection of materials. In the professional module power supply manufacturers can do both, according to the different specifications of the product needs, different application conditions, discard the unnecessary material specifications, select the optimal material specifications required.
Second, the PCB design of the power module. Because the modular power supply product has the PCB design specification requirements of the module power supply, it must consider the heat dissipation design, the EMC design, the interference design and the production process design, etc. The content involved is non-production, so the PCB design is used as the module power supply product development process. One of the most important aspects to deal with is shown in Figure 7.
Figure 7 PCB design requirements
3, reliability test
After the completion of product development, it can not be directly applied. In order to ensure that the product performs its best performance in practical applications, it is usually required to perform each input and output performance test, tolerance test, transient condition test, reliability test, and EMC electromagnetic compatibility test. , high and low temperature test, limit test, life test, safety test and other tests, the standards are shown in Table 1 below. , And many performance indicators of the test should be further detailed to the multi-point test, long-term test, repeat test and batch test, so test a product or a project, short more than half a month, more than a month or more . Zhiyuan Electronics has a full set of test equipment and testing procedures, as shown in Table 2 below.
Table 1 Reliability Test Standards
Table 2 Test Equipment
4, industry application circuit design experience
In other words, “interlaced lines are separated by mountainsâ€. Although power supplies are extremely versatile products, there are thousands of forms of power supply requirements in all walks of life. In order to produce power supply products suitable for their own industry applications, this is not really difficult for DIY users. small. Zhiyuan Electronics has been ploughing power modules for many years. Since the first isolated DC-DC power module was introduced in 2003, it has been favored and accepted by a wide range of users. So far, it has provided users of many different industries with different power isolation solutions, such as public transportation. POS locomotive-carrying power supply, as shown in Figure 8 below; BMS complete system solution can provide a complete set of power and signal isolation scheme, as shown in Figure 8 below.
Figure 8 Bus POS Locomotive Power Supply
Figure 9 BMS power and signal isolation solutions
Fourth, summary
ZLG Zhiyuan Electronics independently researches and develops and produces isolated power supply modules with a wide input voltage range, isolated 1000VDC, 1500VDC, and 3000VDC series, with various package formats, compatible with international standard SIP, DIP, etc., and also according to the special conditions of the project. Provide tailor-made tailor-made services, custom features, special packaged isolated power supply for customers. Zhiyuan Power Module is widely used in electric power, industrial automation, etc. for its high efficiency, wide input voltage range, small size, high reliability, impact resistance, good isolation characteristics, wide temperature range, etc., and is suitable for board-level power supply. Communications, medical, transportation, building automation, instrumentation, and automotive electronics are among many other areas.
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