How to choose a suitable DC power module

Temperature range and derating use

Generally, power modules of manufacturers have several temperature range products to choose from: commercial grade, industrial grade, military grade, etc. when selecting module power supply, we must consider the actual working temperature range, because different temperature grades, different materials and manufacturing processes will cause great price differences, and improper selection will affect the use, so we have to consider carefully. 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 (packaging form), the nominal temperature range of the module must strictly meet the actual needs or even have a little 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 approaches the limit, what should be done? Derating. That is, choose products with larger power or package, so that "big horse pulls small car", and the temperature rise is lower, which can alleviate this contradiction to a certain extent. The derating ratio varies with the power level. Generally, it is 3 ~ 10W / ℃ above 50W. In a word, either choose products with a wide temperature range to make full use of power and have smaller packages, but the price is higher; Or choose products in the general temperature range, the price is lower, and the power margin and packaging form have to be larger. A compromise should be considered.

4. Working frequency

Generally speaking, the higher the operating frequency, the less the output ripple noise, and the better the dynamic response of the power supply. However, the higher the requirements for components, especially magnetic materials, and the cost will increase. Therefore, the switching frequency of domestic modular power supply products is mostly below 300kHz, and even only about 100kHz, which makes it difficult to meet the requirements of dynamic response under variable load conditions, Therefore, products with high switching frequency should be considered for applications with high requirements. On the other hand, when the switching frequency of the module power supply is close to the operating frequency of the signal, it is easy to cause beat oscillation, which should also be considered when selecting. The switching frequency of the power module can reach up to 500KHz, with excellent output characteristics.

5. Isolation voltage

The isolation voltage of power modules used in general occasions 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 statistics show that the failure of module power supply within the expected effective time is mainly caused by damage under external fault conditions. And the probability of failure in normal use is very low. Therefore, an important link to prolong the service life of the module power supply and improve the system reliability is to select 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 permanent failure, and after the external fault 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 should also have over-temperature protection.