How to select the power supply of DCDC module

2022-08-07
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How to select dc/dc module power supply

dc/dc module power supply is increasingly widely used in the fields of communication, network, industrial control, railway, military and so on because of its remarkable characteristics of small size, outstanding performance and convenient use. Many system designers have realized that the correct and reasonable selection of dc/dc module power supply can save the trouble in power supply design and commissioning, and focus on their own professional fields. This can not only improve the reliability and design level of the overall system, but also shorten the R & D cycle of the entire product, and win valuable business opportunities for leading and winning in the fierce market competition. Then, how to correctly and reasonably select the dc/dc module power supply

in addition to the most basic voltage conversion function, the following aspects need to be considered:

1. rated power: it is generally recommended that the actual power used is 30-80% of the rated power of the module power supply (the specific proportion is also related to other factors, which will be mentioned later.), Within this power range, the performance of the module power supply is relatively full, stable and reliable. Too light load causes waste of resources, and too heavy load is detrimental to temperature rise and reliability. All module power supplies have certain overload capacity

2. packaging form: there are various packaging forms of module power supplies, including those conforming to international standards and non-standard ones. For the products of the same company, the same power products have different packaging, and the same packaging has different power. So how to choose the packaging form? There are three main aspects: ① the volume should be as small as possible under certain power conditions, so as to give more space and more functions to other parts of the system; ② Try to choose products that conform to international standard packaging because of good compatibility. 2. Lithium salt production is not limited to oneortwo suppliers; ③ It shall be expandable to facilitate system expansion and upgrading. Select a package. Due to the increased requirements of the system for power supply power due to function upgrading, the package of the power module remains unchanged, and the design of the system circuit board does not need to be changed, which greatly simplifies the product upgrading and saves time. Driven by the "1025" plan

3. temperature range and derating use: the module power supply of general manufacturers has several temperature range products to choose from: commercial grade, industrial grade, military grade, etc. when selecting the module power supply, we must consider the actual operating temperature range, because the prices vary greatly with different temperature grades, materials and manufacturing processes, and improper selection will affect the use, so we have to consider carefully. There are two selection methods: one is to select according to the use power and packaging form. If the actual use power is close to the rated power under a certain volume (packaging form), the nominal temperature range of the module must strictly meet the actual needs or even have a slight margin. Second, the product is selected according to the temperature range. What if the product with a smaller temperature range is selected due to cost considerations, but sometimes the temperature approaches the limit? Derating use. That is, select products with greater power or packaging. In this way, the "big horse pulls the small car", and the temperature rise should be lower, which can alleviate this contradiction to a certain extent. The derating ratio varies with the power level. Generally, the derating ratio above 50W of the 8th China International Automotive Lightweight plastics and innovative materials development forum is 3-10w/℃. In a word, products with a wide temperature range can be selected to make full use of power and package smaller, but the price is higher; Or choose products in the general temperature range with a lower price and a larger power margin and packaging form. Compromise should be considered

4. operating frequency: Generally speaking, the higher the operating frequency is, the smaller the output ripple noise will be and the better the dynamic response of the power supply will be. However, the higher the requirements for components, especially magnetic materials, the higher the cost will be. Therefore, the switching frequency of domestic module power products is mostly below 300kHz, and even some are only about 100kHz, which is difficult to meet the requirements of dynamic response under load changing conditions, Therefore, products with high switching frequency should be considered for high demand applications. On the other hand, when the switching frequency of the module power supply is close to the signal operating frequency, it is easy to cause beat oscillation, which should also be taken into account when selecting

5. isolation voltage: generally, the isolation voltage of the module power supply is not very high, but a higher isolation voltage can ensure that the module power supply has smaller leakage current, higher safety and reliability, and better EMC characteristics. Therefore, the general isolation voltage level in the industry is above 1500vdc

6. fault protection function: relevant statistical data show that the main reason for the failure of module power supply within the expected effective time is the damage under external fault conditions. The probability of failure in normal use is very low. Therefore, an important part of prolonging the service life of the module power supply and improving the reliability of the system is to select products with perfect protection functions, that is, in the fatigue testing machine produced by Shandong Sida hi tech, there are several models of module power supply that are specifically aimed at fatigue life. When the external circuit fails, the module power supply can automatically enter the protection state without permanent failure. After the external failure disappears, it should automatically return to normal. The protection function of module power supply shall at least include input overvoltage, undervoltage and soft start protection; Output overvoltage, overcurrent and short circuit protection, and high-power products shall also have over-temperature protection

7. power consumption and efficiency: according to the formula η= Pout/pin=pout/(pout+p consumption), where pin, pout and P consumption are module power input, output power and self power loss respectively. Thus: it can be seen that under certain output power conditions, the smaller the module loss P consumption, the higher the efficiency, the lower the temperature rise and the longer the service life. In addition to the full load normal loss, there are two other losses worth paying attention to: no-load loss and short-circuit loss (module power loss during output short circuit). The smaller these two losses are, the higher the module efficiency is. In particular, if the short circuit is not taken in time, it may last for a long time. The smaller the short-circuit loss is, the probability of failure is greatly reduced. Of course, the smaller the loss, the more in line with the requirements of energy conservation

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