DC / DC Converter Supply Selection
DC / DC power module with its compact size, outstanding performance, a notable feature of easy-to-use, has been increasingly widely used in communications, networking, industrial control, railways, military and other fields. Many engineers have been aware of: choosing a suitable DC / DC power modules can save design, debugging problems, and focus more in their field. This can not only improve the overall system reliability, and more importantly, shorten the entire product development cycle. So as to win business opportunities in the fierce market competition. So, how to choose correct DC / DC power modules?
In addition to the most basic functions of voltage conversion, you also need to consider the following aspects:
1. Rated Power
General recommendations of the actual use of power is 30 ~ 80% rated power of the power module(the ratio is also related to other factors, will be discussed latter.). Too low loads lead to waste, too high will product too much heat and are relatively not so stable. A waste of resources to load too light, too heavy on the temperature rise, the negative reliability. Most modules have overload protection, like current-logic.com's products usually provide 120 to 150% bearing, but it is not recommended to work long hours under the over load conditions. After all, this is only a short-term protection measure.
Power modules are packaged in a variety of forms. Some are in line with international standards, others are non-standard. The same rated power modules may have different packaging, or the same package have different rated power. So how to choose letters loaded form of it?
There are three major criteria: ①size should be as small as possible in order to save more space for other parts; ② choose types in line with international standards package as far as possible.Because compatibility will be better, and more easy to find replacing supplier; ③ should have the scalability, ease of system expansion and upgrading.
Take current-logic.com's high-power line as an example, they are fully in line with international standards of widely used semi-brick, full brick package, are fully compatible with VICOR, LAMBDA and other well-known brands. The half brick products cover power 50 ~ 200W, full bricks cover 100 ~ 300W.
3. Derating temperature range
Power module manufacturers usually have a few temperature range available: Commodity-grade, industrial-grade, military rank, etc. When choosing module power must take into account the actual needs of the operating temperature range. Different temperature level use different materials and processes, so prices vary greatly. There are two choosing method: One is based on the use of power and package, if the use of power are close to the actual rated power, then the nominal temperature range modules must strictly meet the actual needs with even a slight margin. Second, choose in accordance to the temperature range. If a smaller temperature range is chosen as a result of considering the cost, but the temperature approaches now and then the limits of the situation, what should we do? Derating use. Choose higher power or greater package products, to lower the temperature rise. Thus can be alleviated this contradiction to some extent. Derating ratio of different grades vary with the power, generally is 3 ~ 10W / ℃ above 50W. In short, choice of wide temperature range, the power can be used more fully and smaller package, but higher prices; choice of temperature range or products, lower prices, larger power margin and package.
4. Operating frequency
Generally speaking the higher the frequency, the smaller output ripple noise, the better dynamic response. But the cost will increase, particularly the magnetic components. In the market, power module switching frequency are mostly under 300kHz, or even about 100kHz. They will be difficult to meet dynamically response requirements. User should consider the use of high switching frequency products inapplications of strict requirements . The other hand, when the power module switch frequency is close to the signal frequency, syntonic oscillation will easily occur. User should also take this into account. Current-logic.com power modules have witching frequency up to 500kHz, with excellent output characteristics.
5. Isolation voltage
In general occasions, very high isolation voltage requirements are not needed. However, a higher isolation voltage can ensure power supply module has a smaller leakage current, higher reliability, and better EMC characteristics. Isolation voltage of 1500VDC or above is the level generally accepted.
6. Fault protection
Relevant statistical data shows that, if the power modules in effective life-time out of work, the main reasons for failure is damage caused by external fault conditions. The normal probability of failure is very low. Therefore, to extend of the power module life and improve system reliability, it is important to choose products with comprehensive protection functions. That is to choose products that will automatically protect themselves when external circuit failed to work, and recover to normal automatically after the correction of an external fault. Power module protection function should include at least input over-voltage, under-voltage, soft-start protection, output overvoltage, overcurrent, short circuit protection. High-power products should have the over-temperature protection.
For a given output power under certain conditions, the smaller loss of consumption, the higher the efficiency, lower temperature rise, and longer life. In addition normal loss under full load, there are two noteworthy loss: loss of no-load and loss of short circuit (the smaller loss when output short-circuit the higher efficiency is the module). And of course, the smaller the loss is also more in line with the requirements of energy conservation.