Selection Elements of DC/DC Module Power Supply
Rated power
It is generally recommended that the actual power used is 30-80% of the rated power of the module power supply. Within this power range, the performance of the module power supply in all aspects is fully utilized and stable and reliable. A light load causes resource waste, while a heavy load is detrimental to temperature rise, reliability, and other factors.
Packaging form
There are various packaging forms for modular power supplies, including those that comply with international standards and non-standard ones. For the same company's products, the same power product has different packaging, and the same packaging has different power. So how to choose the packaging form? There are mainly three aspects:
Under certain power conditions, the volume should be as small as possible in order to provide more space and functionality for other parts of the system;
2. Try to choose products that comply with international standard packaging, as they have good compatibility and are not limited to one or two suppliers;
3 should have scalability to facilitate system expansion and upgrading.
Choose a packaging method. Due to the increased power requirements for the system due to functional upgrades, the power module packaging remains unchanged, and the system circuit board design does not need to be modified, greatly simplifying product upgrades and saving time.
Temperature Range and Derating Usage
Generally, module power supplies from manufacturers have several temperature range products to choose from: commercial grade, industrial grade, military grade, etc. When selecting module power supplies, it is necessary to consider the actual operating temperature range, because different temperature levels, materials, and manufacturing processes can result in significant price differences. Improper selection can also affect usage, so careful consideration is necessary. There are two ways to choose:
One is to choose based on the usage power and packaging form. If the actual usage power is close to the rated power under certain conditions of volume (packaging 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 based on the temperature range.
What if a product with a smaller temperature range is chosen due to cost considerations, but sometimes the temperature approaches the limit? Reduced usage. Choosing products with higher power or packaging can alleviate this contradiction to a certain extent by reducing the temperature rise of the "big horse pulling the small car". The reduction ratio varies with different power levels, generally ranging from 3 to 10W/℃ for power levels above 50W. In short, either choose products with a wide temperature range for better power utilization and smaller packaging, but at a higher price; Either choose products with a general temperature range, lower prices, and larger power margins and packaging forms. Compromise should be considered.
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 components, especially magnetic materials, the higher the cost. Therefore, the switching frequency of domestic modular power supply products is mostly below 300kHz, and some even only have around 100kHz, which makes it difficult to meet the requirements of dynamic response under load changing conditions. Therefore, in high demand applications, products with high switching frequencies should be considered. 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 also be considered when selecting.
Isolation voltage
In general, there is not a high requirement for the isolation voltage of the module power supply, 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 commonly used isolation voltage level in the industry is above 1500VDC.
Fault protection function
According to statistical data, the main reason for the failure of module power supply within the expected effective time is damage under external fault conditions. The probability of failure during normal use is very low. Therefore, an important part of extending the lifespan of module power supplies and improving system reliability is to choose products with complete 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. After the external fault disappears, it should be able to automatically restore normal operation. The protection function of the module power supply should at least include input overvoltage, undervoltage, and soft start protection; Output overvoltage, overcurrent, short circuit protection, and high-power products should also have over temperature protection.
Power consumption and efficiency
According to the formula, Pin, Pout, and P losses are the module power input, output power, and self power losses, respectively. From this, it can be seen that under certain output power conditions, the smaller the module loss P, the higher the efficiency, the lower the temperature rise, and the longer the lifespan. In addition to normal losses at full load, there are also two losses worth noting: no-load losses and short-circuit losses (module power loss during output short-circuit), because the smaller these two losses, the higher the efficiency of the module, especially in cases where short-circuit measures are not taken in a timely manner, which may last for a longer time. The smaller the short-circuit losses, the greater the probability of failure. Of course, the smaller the loss, the more in line with energy-saving requirements.
