How to select DC/DC module power
發(fā)布日期：2017-04-21 13:36:22
The DC/DC module power supply with its small size, good performance, convenient features, has been widely used in communication, network, industrial control, railway, military and other fields. Many system designers have realized: the DC/DC power module correctly, you can debug the power supply design, save trouble, will mainly focus on their own areas of expertise, so that not only can improve the overall system reliability and design level, and it is more important to shorten the product development cycle, leading to success to win the precious opportunities in the fierce competition in the market. Then, how to choose the DC/DC module power supply correctly and reasonably?
Choose to use the DC/DC module power, in addition to the most basic voltage conversion function, there are several aspects to consider:
1. rated power: generally recommended the actual use of power is module power rating of 30 to 80% is appropriate (specific proportion is also related to other factors, will be mentioned later) In this power range, all aspects of module power performance are relatively adequate and stable and reliable. The load is too light, waste of resources, too heavy for temperature rise, reliability and other disadvantages. All modules have the power overload capacity
2. package: a package form of power module is diverse, in line with international standards is also non standard is also the same in terms of the company's products, the same power products have different package, the same package has different power, so how to choose the package? There are three main aspects: first, under the condition of certain power volume to be as small as possible, so as to give the rest of the system more and more space; the choice as far as possible in line with international standards of packaging products, because of better compatibility, not limited to one or two suppliers; it should be scalable, easy expansion and upgrade system. Choose a package to upgrade the power system due to functional requirements to improve the power module packaging system remains unchanged, circuit board design can not be changed, which greatly simplifies the upgrading of products upgrading, saving time.
3. temperature range and derating: power module manufacturers generally have several temperature range of products available for use: commercial grade, industrial grade, military grade, in the selection of power supply module must consider the actual needs of the working temperature range, because the temperature level of different materials and manufacturing process of different price difference, selection improper use will affect, so to take into account. You can have two options: one method is based on the use of power and package selection, if the volume (package) under certain conditions the actual use of power is close to the rated power, then the nominal temperature range module must be strictly meet the actual needs and even a slight margin. Two, according to the range of temperature to choose, if because of cost considerations, choose a smaller temperature range of products, but sometimes also have temperature approaching the limit, how to do? Derating. Choose the power or a larger package of products, so "big horse cart", the temperature rise to lower, can alleviate this contradiction to some extent. The derating ratio varies with the power level, and the average 50W is over 3 to 10W/ degrees centigrade. In a word or a wide temperature range of products, make full use of power, the package is also smaller, but the price is high; either the general temperature range of products, price, power margin and package is big and should be a compromise.
4. working frequency: generally the higher the frequency of output ripple noise is smaller, the power dynamic response is better, but the components especially the magnetic material requirements are also higher, the cost will be increased, so the switching frequency of the domestic power supply module products are below 300kHz, and even some only about 100kHz, so it is difficult to meet the dynamic response under the condition of variable load, therefore high demand to consider the application of high frequency switching products. On the other hand, when the module power switch frequency is close to the signal operating frequency, it is easy to cause a beat oscillation, which should be taken into consideration when choosing the power switch frequency.
Isolation of module power supply voltage: 5. isolation voltage requirements are not very high general occasions, but isolated higher voltage can guarantee the power supply module has smaller leakage current, higher safety and reliability, and EMC characteristics is better, so the current industry generally isolated voltage level is above 1500VDC.
6. fault protection function: the statistical data show that the main reason for the failure of the module power within the expected effective time is the damage under external fault conditions. The probability of normal use failure is very low. Therefore, prolong the life and improve the reliability of the system power supply module is an important part of the selection of perfect protection products, namely failure in the power supply module external circuit module when the power supply can automatically enter the state of protection without permanent fault, external fault can be automatically recovered after the disappearance. The protection function of module power supply shall include input overvoltage, undervoltage, soft start protection, output over-voltage, over-current and short circuit protection, and high power product should have over temperature protection, etc..
7. power and efficiency: according to the formula of ETA =Pout/Pin=Pout/ (Pout+P, Pin, Pout consumption), P consumption respectively module power input and output power and its power loss. Thus, it can be seen that under the certain output power, the module loss P consumption is smaller, then the efficiency is higher, the temperature rise is low, and the life is longer. In addition to full load loss, two losses are noted: no-load loss and short-circuit loss (module power supply during short circuit output)
Choose to use the DC/DC module power, in addition to the most basic voltage conversion function, there are several aspects to consider:
1. rated power: generally recommended the actual use of power is module power rating of 30 to 80% is appropriate (specific proportion is also related to other factors, will be mentioned later) In this power range, all aspects of module power performance are relatively adequate and stable and reliable. The load is too light, waste of resources, too heavy for temperature rise, reliability and other disadvantages. All modules have the power overload capacity
2. package: a package form of power module is diverse, in line with international standards is also non standard is also the same in terms of the company's products, the same power products have different package, the same package has different power, so how to choose the package? There are three main aspects: first, under the condition of certain power volume to be as small as possible, so as to give the rest of the system more and more space; the choice as far as possible in line with international standards of packaging products, because of better compatibility, not limited to one or two suppliers; it should be scalable, easy expansion and upgrade system. Choose a package to upgrade the power system due to functional requirements to improve the power module packaging system remains unchanged, circuit board design can not be changed, which greatly simplifies the upgrading of products upgrading, saving time.
3. temperature range and derating: power module manufacturers generally have several temperature range of products available for use: commercial grade, industrial grade, military grade, in the selection of power supply module must consider the actual needs of the working temperature range, because the temperature level of different materials and manufacturing process of different price difference, selection improper use will affect, so to take into account. You can have two options: one method is based on the use of power and package selection, if the volume (package) under certain conditions the actual use of power is close to the rated power, then the nominal temperature range module must be strictly meet the actual needs and even a slight margin. Two, according to the range of temperature to choose, if because of cost considerations, choose a smaller temperature range of products, but sometimes also have temperature approaching the limit, how to do? Derating. Choose the power or a larger package of products, so "big horse cart", the temperature rise to lower, can alleviate this contradiction to some extent. The derating ratio varies with the power level, and the average 50W is over 3 to 10W/ degrees centigrade. In a word or a wide temperature range of products, make full use of power, the package is also smaller, but the price is high; either the general temperature range of products, price, power margin and package is big and should be a compromise.
4. working frequency: generally the higher the frequency of output ripple noise is smaller, the power dynamic response is better, but the components especially the magnetic material requirements are also higher, the cost will be increased, so the switching frequency of the domestic power supply module products are below 300kHz, and even some only about 100kHz, so it is difficult to meet the dynamic response under the condition of variable load, therefore high demand to consider the application of high frequency switching products. On the other hand, when the module power switch frequency is close to the signal operating frequency, it is easy to cause a beat oscillation, which should be taken into consideration when choosing the power switch frequency.
Isolation of module power supply voltage: 5. isolation voltage requirements are not very high general occasions, but isolated higher voltage can guarantee the power supply module has smaller leakage current, higher safety and reliability, and EMC characteristics is better, so the current industry generally isolated voltage level is above 1500VDC.
6. fault protection function: the statistical data show that the main reason for the failure of the module power within the expected effective time is the damage under external fault conditions. The probability of normal use failure is very low. Therefore, prolong the life and improve the reliability of the system power supply module is an important part of the selection of perfect protection products, namely failure in the power supply module external circuit module when the power supply can automatically enter the state of protection without permanent fault, external fault can be automatically recovered after the disappearance. The protection function of module power supply shall include input overvoltage, undervoltage, soft start protection, output over-voltage, over-current and short circuit protection, and high power product should have over temperature protection, etc..
7. power and efficiency: according to the formula of ETA =Pout/Pin=Pout/ (Pout+P, Pin, Pout consumption), P consumption respectively module power input and output power and its power loss. Thus, it can be seen that under the certain output power, the module loss P consumption is smaller, then the efficiency is higher, the temperature rise is low, and the life is longer. In addition to full load loss, two losses are noted: no-load loss and short-circuit loss (module power supply during short circuit output)
