The central issue of DCDC module power supply:
This article refers to the address: http://
How to choose DC/DC module power supply correctly and reasonably
DCDC module power supply solution:
Rated power considerations
Package form considerations
Choose the right temperature range and derating
Isolation voltage considerations
Power and efficiency considerations
DC/DC module power supply is widely used in communication, network, industrial control, railway, military and other fields due to its remarkable size, excellent performance and convenient use. Many system designers have realized that correct and reasonable selection of DC/DC module power supply can save troubles in power supply design and debugging, and concentrate on their own professional fields, which can not only improve the reliability and design level of the overall system. And more importantly, it shortened the development cycle of the entire product and won valuable business opportunities for leading the competition in the fierce market competition. Then, how to correctly and reasonably select the DC/DC module power supply, the author will talk about this issue from the perspective of DC/DC module power supply development and design, for the reference of the system designers.
Several aspects to consider when selecting a power module
rated power
Package form
Temperature range and derating
Isolation voltage
Power consumption and efficiency
rated power
It is generally recommended that the actual power used is 30 to 80% of the rated power of the module. The specific ratio is also related to other factors, which will be mentioned later. The performance of all aspects of the module power supply is sufficient and stable in this power range. reliable. Too light a load causes waste of resources, and too heavy is unfavorable for temperature rise and reliability. All module power supplies have a certain overload capacity, but it is still not recommended to work under overload conditions for a long time. After all, this is a short-term emergency plan.
Package form
The form factor and output form of the DC/DC converter vary widely. Low-power products use a sealed enclosure that is very small in size; high-power products are often in the form of quarter-brick or half-brick, circuited or exposed, or wrapped in a casing. When choosing, you need to pay attention to the following two aspects: first, whether the pins are on the same plane; second, whether it is easy to solder. Converters in the form of SMT must comply with the requirements of the IEC 191-6:1990 standard, which imposes strict limits on the coplanarity of the pins of SMT devices. The fact that the device pins are not coplanar will cause difficulty in positioning the device during assembly, which will seriously affect the soldering quality and increase the defect rate. Converters in the form of SMT shall be capable of withstanding the specified welding conditions. For most modern pipelines, the device must meet the reflow requirements specified in the CEC00802 standard, ie the device surface temperature can exceed 300 °C. If the converter does not meet this requirement, it will need to design a special welding assembly process, which will increase assembly time and increase production costs.
Module power supply packages are available in a variety of ways, in accordance with international standards, non-standard, as well as the same company products, the same power products have different packages, the same package has different power, then how to choose the package form? There are three 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 standards, because compatibility is better, not limited to one or two suppliers. ;3 should be scalable to facilitate system expansion and upgrade. Selecting a package, the system requires higher power supply requirements due to functional upgrades, the power module package remains unchanged, and the system board design can be modified without modification, which greatly simplifies product upgrades and saves time. All are in line with international standards, and are widely used in the industry in half-brick and full-brick packaging. They are fully compatible with famous brands such as VICOR and LAMBDA, and the half-brick product power range covers 50-200W, and the whole brick product covers 100-300W.
Temperature range and derating
General manufacturer's module power supply has several temperature range products available: commercial grade, industrial grade, military grade, etc., when selecting the module power supply must consider the actual operating temperature range, because the temperature grade is different materials and manufacturing processes Prices vary widely, and improper selection can affect usage, so they have to be carefully considered. There are two options: one is to choose according to the power and package form. If the actual power is close to the rated power under certain conditions of volume (package form), then the nominal temperature range of the module must strictly meet the actual needs or even Slightly marginal. 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 there is a temperature approaching the limit, what should I do? Derating. That is to choose the power or package a larger product, so that the "big horse car", the temperature rise is lower, can alleviate this contradiction to some extent. The derating ratio varies with the power level, and is generally 3 to 10 W/° C above 50 W. In short, you can choose a wide temperature range of products, the power is more fully utilized, the package is smaller, but the price is higher; either the general temperature range is selected, the price is lower, the power margin and package form are larger. Should be compromised.
Commercial grade (0 °C to +70 °C)
Industrial grade (-40 °C to +85 °C)
Military grade (-55 °C to +125 °C)
Frequency conversion and fixed frequency
Like all switching devices, the DC/DC converter generates noise during operation, so the filtering performance is also an important selection basis. Integrated DC/DC converters typically use variable frequency switching technology or fixed frequency switching technology. Converters using variable frequency switching technology are subject to constant adjustment based on load conditions, which leads to band broadening and increased filter complexity. The fixed-frequency switching converter is much simpler in this respect, and even LC filters can be used.
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 on components, especially magnetic materials, the higher the cost, so the switching frequency of domestic module power products is higher. In order to be below 300 kHz, and even some are only about 100 kHz, it is difficult to meet the dynamic response requirements under load-changing conditions. Therefore, high-requirement applications should consider products with high switching frequency. On the other hand, when the module power switch frequency is close to the signal operating frequency, it is easy to cause beat oscillation, and this should be taken into consideration when selecting.
Isolation
Most circuits must be isolated, that is, the load and the load are separated from the noise of the local power supply from other loads and noise on the grid. Only isolated converters can achieve this. In addition to the above requirements, an isolated converter can be used to achieve differential output and bipolar output (see figure). In addition, the output high voltage terminal of the isolated converter is connected to the power ground of the load to form a negative power source. Since the voltage reference point is not ground, the load can achieve a higher voltage. Another advantage of using an isolated converter is that multiple converters with different output voltages can be cascaded to form a single power supply. This feature is useful for devices where the output voltage of a single converter does not meet operating voltage requirements. The maximum voltage applied between the input and the output that the converter can withstand for a certain period of time (usually 1 second) is called the isolation strength of the converter. The rated operating voltage of the converter refers to the voltage applied to the input terminal that the converter can withstand for a long time. This voltage is lower than the isolation strength. When selecting an isolated converter, it is also necessary to consider the leakage current indicator of the device. The leakage current refers to the current generated by the coupling capacitance between the input circuit and the output circuit. As long as the value of the isolation capacitor is given and the noise frequency is determined, the magnitude of the leakage capacitance can be calculated from the impedance. The leakage current increases as the noise voltage increases and decreases as the isolation capacitance decreases. Therefore, when designing a low-noise power supply, a DC/DC converter with high isolation strength and low isolation capacitance should be selected to reduce leakage current.
Usually, a high isolation voltage is required in medical equipment, so that the leakage current is small and the harm to the body is small. In general, the power supply isolation voltage requirement for the module is not very high, but the higher isolation voltage can ensure that the module power supply has less leakage current, higher safety and reliability, and better EMC characteristics. The universal isolation voltage level is above 1500 VDC.
What is a surge?
Surge, known as transient over-current, is a transient current, voltage fluctuation that occurs in a circuit and typically lasts about one millionth of a second in a circuit. A voltage fluctuation of 5,000 or 10,000 volts in a 220 volt circuit system that lasts for a moment (one millionth of a second), that is, a surge or transient overcurrent.
Sources of Surge: In simple terms, there are two aspects: external surges and internal surges. Surge from the outside: The main source is lightning. When there is charge accumulation in the cloud layer, and the surface under the cloud layer collects the same amount of charge of opposite polarity, lightning discharge occurs. The charge potential between the cloud layer and the ground is up to several million volts. When lightning strikes, several thousand The ammeter's current is discharged through a lightning strike, and passes through all the equipment and the earth back to the cloud, thus completing the electrical path. Unfortunately, access is often an important or expensive device. If a lightning strikes a nearby power line, some of the current will enter the building along the line. This huge current will directly disrupt or destroy the computer and other sensitive electrical equipment. The speed is as fast as a millionth of a second. .
Another source of external surges is the overvoltage generated by the utility's utility grid switch on the power line.
Surge from inside: 88% of surges are generated in buildings such as air conditioners, elevators, welders, air compressors, pumps, switching power supplies, copiers and other inductive loads. The harm of power surge to computers and other sensitive electrical equipment: Computer technology has developed to date, multi-layer, ultra-scale layered chips, circuit-intensive, tend to be more integrated, smaller component gaps, and thinner wires. A few years ago, one square centimeter of computer chips had 2,000 transistors and now the Pentium has more than 10,000,000. This increases the probability that the computer will be damaged by the surge.
Due to the design and construction of the computer it is determined that it should operate within a specific voltage range. When the power surge exceeds the level that the computer can withstand, the computer will be garbled, the chip will be damaged, and the components will age prematurely. These symptoms include: unexpected data errors, failure to receive/deliver data, lost documents, malfunctions, and often Need repairs, unexplained failures and hardware problems, etc.
Lightning surges far exceed the levels that computers and other electrical equipment can withstand. In most cases, computers and other electrical equipment are destroyed immediately, or data is lost forever. Even a 20-horsepower small induction engine can generate 3,000-5,000 volts of surge, causing a computer that shares the same distribution box to be damaged or interfered with each surge. The number of surges is very frequent.
Will surges damage those electrical equipment?
Electrical equipment containing microprocessors is extremely vulnerable to power surges, including computer and computer auxiliary equipment, program controllers, PLCs, fax machines, telephones, message machines, etc.; program-controlled switches, broadcast television transmitters, microwave relays Equipment; products in the home appliance industry include televisions, stereos, microwave ovens, video recorders, washing machines, dryers and refrigerators. According to US survey data, 63% of electrical products that have problems during the warranty period are caused by power surges.
Source of power surge
The surge can come from outside the electrical device or from inside the electrical device, ie from electrical equipment within the electrical device. Surge surges from the outside are caused by lightning or utility grid switching. Both types of harmful power disturbances can disrupt the operation of computer and computer information processing systems, causing downtime or permanent equipment damage.
When there is charge on the cloud, the lower surface of the cloud produces an equivalent charge of opposite polarity, which will cause lightning discharge. The latter situation is like the discharge of a large battery pack or a large capacitor, and the charge potential between the cloud and the ground is as high as several million volts. In the event of a lightning strike, a current of several kiloamperes is discharged through a lightning strike, and all equipment and the earth return to the cloud layer to complete the electrical path. Unfortunately, this lightning path often takes important or expensive equipment. The key concept of surge protection is to provide a short, efficient path to the lightning induced current to the earth. This lightning surge will be shunted from outside the equipment. Large lightning current values ​​are often exemplified, but in fact it is unlikely. For example, Bellcore engineers set the bleeder current of the surge protector to 20000A (see reference TR-NWT-001011). Although they empirically set the maximum peak current in their electrical equipment to 10,000A, they still take a 100% safety factor, which is to set the bleeder current of the surge protector to 2000A. The chance of a lightning strike current of 210,000 A (one of the highest recorded values) in the exposed area of ​​the line is only 0.5% of the total lightning strike chance. Such a large lightning current rarely occurs in the building power supply line, but it is still necessary to pay attention to the prevention of such external surges. Surge from the inside comes from internal surges, such as surges from air conditioners, air compressors, electric arc welders, electric pumps, elevators, switching power supplies, and other inductive loads. For example, a 20 hp induction motor (line voltage 230V, class 4, Y-junction) has a stored energy of about 39J per phase at maximum torque, and it will generate transients when its nominal square root current is cut off. Overvoltage. It often occurs, and other loads that it supplies from the same distribution box will therefore be susceptible to damage or malfunction. Do not assume that the overvoltage protector on the electrical equipment inlet line protects the electrical equipment from internal surges. It can't, it can only prevent external surges entering the electrical device along the power line, because the large-capacity incoming line protector is too far away from the internal surge.
Mean time between failures
Many DPA systems require a high degree of reliability, which places demands on the Mean Time Between Failure (MTTF). It is necessary to remind readers that the data on the product manual cannot evaluate the reliability of a product. The reason for this problem is that there is no recognized definition and calculation standard for MTTF indicators in the world. The "general" reliability prediction method in the US military standard MIL-HDBK-217F is commonly used by various manufacturers. And the telecom equipment model in the Bellcore standard TR-NWT-000332. However, even MTTF indicators that are claimed to follow the same standard are often inconsistent. The first source of this inconsistency is the different treatment of component characteristics in the calculation formula (for example, some calculations ignore the influence of solder joints, and solder joint failure is one of the most common causes of circuit failure); The second is the reliability index of components. For example, some vendors use device data and failure rate data from MIL-HDBK-217F, while others use data from other sources. The third source is the difference in specific calculation methods (even MIL-HDBK). Two different forecasting tools are given). Of course, any MTTF indicator is meaningless until the converter is put into use. Temperature has a significant impact on reliability. The empirical formula is: for every 10 °C increase in ambient temperature, the lifetime of the device will be reduced by half. If the main equipment needs to operate at 40 ° C ~ 50 ° C, and the temperature of the power supply components is higher than the ambient temperature of 20 ° C, then the MTTF indicator calculated at 25 ° C will lose its meaning. Practice has proved that designers must thoroughly understand the way manufacturers estimate MTTF through the data in the product manual. You must go through the detailed steps of the inference and know the source of the original data and its measurement conditions. For those vendors that cannot provide detailed information, they should have reservations about their indicators.
Relevant statistics indicate that the main cause of failure of the module power supply within the expected effective time is damage under external fault conditions. The probability of failure of normal use is very low. Therefore, an important part of extending the power life of the module and improving the reliability of the system is to select a product with perfect protection function, 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 the external fault should be able to disappear. Automatically resumes normal. The protection function of the module power supply should include at least input overvoltage, undervoltage, soft start protection; output overvoltage, overcurrent, short circuit protection, high power products should also have over temperature protection.
Power consumption and efficiency
According to the formula, the Pin, Pout, and P consumptions are the module power input, output power, and self power loss, respectively. It can be seen that under certain conditions of output power, the smaller the module loss P consumption, the higher the efficiency, the lower the temperature rise and the longer the life. In addition to full load normal loss, there are two losses worth noting: no-load loss and short-circuit loss (module power loss at output short-circuit), because the smaller the two losses, the higher the module efficiency, especially the short-circuit is not taken in time. In the case of measures, it may last for a long time, and the smaller the short-circuit loss, the greater the probability of failure. Of course, the smaller the loss, the more energy-efficient.
Soft-switching technology: In order to improve the conversion efficiency of the converter, various soft-switching technologies are used, representative of passive soft-switching technology and active soft-switching technology, mainly including zero-voltage switching/zero-current switching (ZVS/ ZCS) Resonant, quasi-resonant, zero-voltage/zero-current pulse-width modulation (ZVS/ZCS-PWM) and zero-voltage transition/zero-current transition pulse-width modulation (ZVT/ZCT-PWM). The soft switching technology can effectively reduce the switching loss and switching stress, which helps to improve the conversion efficiency of the converter.
LED Tunnel Lamp is an attractive, functional and weather-resistant feature.Tunnel lamps and lanterns;Die casting aluminum process and aluminum alloy forming process;Strong structure and strong impact resistance;The heat dissipation performance can guarantee the permanent work of lamps in the harsh working environment of the tunnel.Efficient and reliable constant current.Power supply can make lamps work stable and live longer;This lamp also can serve as gas station illume, charge.Station lighting and other ceiling working environment.
Led Tunnel Lamp,Rapidcure Led Tunnel Lamp,Smart Tunnel Led Lamp,Led Lamp
Jiangsu chengxu Electric Group Co., Ltd , http://www.chengxulighting.com