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Selection of dcdc module power supply

Edit:Nanjing Fulaixiang Electronics Co., Ltd.UpDate:2018-06-28

Choose to usedcdc module power supplyIn addition to the basic voltage conversion function, the following aspects need to be considered:

1. rated power

Generally, it is recommended that the actual power used is 30-80% of the rated power of the module power supply (the specific ratio is also related to other factors, which will be mentioned later.). All aspects of the module power supply performance within this power range are fully and stable. reliable. Too light load causes waste of resources, and too heavy load is detrimental to temperature rise and reliability. All module power supplies have a certain overload capacity. For example, the products of the following companies can reach 120-150%, but it is still not recommended to work under overload conditions for a long time. After all, this is a short-term emergency measure.

2. Package form

There are various packaging forms of module power supplies. There are also international standards and non-standard ones. For the same company's products, the same power product has different packages, and the same package has different power. Then how to choose the package 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 functions to other parts of the system;

② Try to choose products that conform to international standard packaging, because of better compatibility, it is not limited to one or two suppliers;

③ It should be expandable to facilitate system expansion and upgrade. Choose a package. Due to the increased power requirements of the system due to function upgrades, the power module package remains unchanged, and the system circuit board design does not need to be changed, which greatly simplifies product upgrades and saves time. Take Ding Lixin’s high-power module power products as an example: all comply with international standards, are half-brick and full-brick packages widely used in the industry, are fully compatible with famous brands such as VICOR, LAMBDA, and the power range of half-brick products covers 50-200W Full brick products cover 100~300W.

3. Temperature range and derating use

Generally, the module power supplies of manufacturers have several temperature range products to choose from: commercial grade, industrial grade, military grade, etc. When choosing a module power supply, the actual operating temperature range must be considered, because the temperature grade is different, the material and manufacturing process are different. Prices vary greatly, and improper selection will also affect the use, so we have to carefully consider. There are two options:

One is to choose according to the use power and packaging form. If the actual use power is close to the rated power under a certain volume (package form), then the nominal temperature range of the module must strictly meet the actual needs or even have a slight margin.

The second is to choose according to the temperature range. If a product with a smaller temperature range is selected due to cost considerations, but sometimes the temperature is approaching the limit, what should I do? Use derating. That is to choose a product with a larger power or package, so that the temperature rise of the "big horse-drawn car" will be lower, which can alleviate this contradiction to a certain extent. The derating ratio varies with different power levels, generally 3~10W/℃ above 50W. In short, either choose a product with a wide temperature range, which has more full power utilization and a smaller package, but the price is higher; or choose a product with a general temperature range, which has a lower price, and a larger power margin and package form. A compromise should be considered.

4. working frequency

Generally speaking, the higher the operating frequency, the smaller the output ripple noise, and the better the dynamic response of the power supply. However, the higher the requirements for the components, especially the magnetic materials, the higher the cost, so the domestic module power products have more switching frequencies. In order to be below 300kHz, even some only about 100kHz, it is difficult to meet the requirements of dynamic response under load changing conditions, so high-demand applications should consider using products with high switching frequency. 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, and this should be taken into consideration when selecting. The switching frequency of Ding Lixin's module power supply can reach up to 500kHz, and it has excellent output characteristics.

5. Isolation voltage

In general occasions, the isolation voltage requirements of the module power supply are not very high, but higher isolation voltage can ensure that the module power supply has smaller leakage current, higher safety and reliability, and better EMC characteristics. Therefore, the current industry The general isolation voltage level is above 1500VDC.

6. Fault protection function

Relevant statistics show that the main reason for the failure of the module power supply within the expected effective time is damage under external fault conditions. The probability of failure in normal use is very low. Therefore, an important part of extending the life of the module power supply and improving the system reliability is to choose products with perfect protection functions, that is, when the external circuit of the module power supply fails, the module power supply can automatically enter the protection state without long-term failure. Automatically return to normal. The protection functions of the module power supply should include at least input overvoltage, undervoltage, and soft-start protection; output overvoltage, overcurrent, and short circuit protection, and high-power products should also have over-temperature protection.

7. Power consumption and efficiency

According to the formula, Pin, Pout, and P consumption are respectively the module power input, output power and its own power loss. It can be seen that under certain conditions of output power, the smaller the module loss P, the higher the efficiency, the lower the temperature rise, and the longer the service life. In addition to the normal loss at full load, there are two other losses worth noting: no-load loss and short-circuit loss (module power loss when the output is short-circuited), because the smaller these two losses, the higher the efficiency of the module, especially if the short-circuit is not taken in time. In the case of measures, it may last for a longer time, and the smaller the short-circuit loss, the greater the probability of failure. Of course, the smaller the loss, the more it meets the requirements of energy saving.

In short, the power supply module, like other components, can only be brought into full play by careful selection and reasonable application, the reliability is fully guaranteed, and the module power supply will be more widely used!