How to choose medical power supply

  Medical power supply is one of the power supplies, it can be said that medical power supply in line with some characteristics of the medical field. In order to improve everyone's understanding of medical power supply, this article will introduce the medical power supply and the selection criteria of medical power supply. If you are interested in medical power, you may wish to continue reading with Xiaobian.

  First, medical power supply

In today's society, with the continuous progress of science and technology, more and more modern medical devices have been rapidly developed, especially electronic instruments directly in contact with the human body, in addition to the increasingly high requirements for the performance of the instrument itself, the consideration of human safety is also becoming more and more concerned. For example: heart puncture monitor, ultrasound, maternal and child monitor, baby temperature preservation instrument, life monitor and some other instruments that are in close contact with the human body, that is to say, patients cannot use the instrument because of the use of the instrument and cause any danger to the human body or other aspects. Unlike other electronics and power electronics, which are targeted at mass market and cost-conscious consumer electronics and other low-cost product applications, medical electronics have many more rules to follow. If the designer is responsible for the system power design, the first question to consider for the power supply part of the system is: buy or manufacture the relevant solution. Since medical electronics production is generally relatively low, designers must consider the issue of buying or homemade. Designers of medical electronics rarely consider designing off-line power supplies themselves. Because the investment required for this particular design and testing is not commensurate with the final volume scale, the equipment manufacturer will find it difficult or impossible to share the investment in the design phase with the volume of the product. Therefore, it is more cost-effective to purchase power supplies directly from companies that already have the corresponding professional design capabilities and testing technologies.

  In commercial application design, if the quality is guaranteed, it is easy to directly select the lowest price power supply product after shopping around. At this time, the lowest price but "passable" product is often the winner, and the best product is not popular. That's fine for disposable electronics that will soon be discarded or don't need repair, but what's the risk if designers just pick one of these power sources and use it in a medical system? The value of medical electronics is high and there are some critical tasks that need to be accomplished. When the health care system fails, the consequences are not as simple as missing a game or taking the wrong train. The proper operation of medical equipment is vital to life and death, especially the power supply of medical equipment, which must comply with the relevant regulations in terms of safety, leakage, EMI-RFI radiation and protection. These standards and related safety codes constitute a set of stringent normative requirements. The power supply used in these demanding applications must meet strict specifications in terms of insulation measures to prevent electrocution for patients and medical personnel. EMC is also a key issue, both in terms of how to reduce electromagnetic radiation and how to protect against it. Therefore, for the design of medical power supplies, the first choice must be the quality and reliability of the product. Commercial power supplies are often confused with medical power supplies by designers, and manufacturers of various low-cost power supplies for the mass market may sell these commercial power supplies as medical power supplies without modification. In this regard, buyers must be careful, because the desire for cheap and choose such power products will lead to terrible consequences. Therefore, designers need to understand the relevant rules and regulations.

  Second, choose what indicators of medical power supply

  1. Requirements for EMC indicators:

The conduction and radiation of medical devices need to meet EN55011, the same limits as EN50552 ITE devices. Considering that the medical system must meet the requirements of high safety and high isolation, conduction and radiation and requirements to meet the standard requirements, which is a big test for the design of the power supply, designers in the design to ensure both high isolation and to do a good job of EMI, in fact, it is a very difficult thing, so many medical equipment also have to compromise, Only the EMI performance must meet the CLASSA level.

  2. Safe distance and pressure resistance:

Medical standards are different from conventional certification. In order to ensure safety and reliability, the standard clearly specifies the safety distance and pressure resistance index requirements of the system. These distance and pressure resistance requirements are differentiated according to the application and population, and are divided into MOPP (patient protection mode) and MOOP (operator protection mode) according to the protection mode. According to the type of equipment is divided into B class, BF class, CF class. Taking into account the versatility of the module, medical power engineers usually meet the most demanding requirements as far as possible in the design process, as simple as: ①L, N to PE 1500VAC isolation, electrical gap 2.5mm, creepage distance 4.0mm. ② The primary side of the transformer is 4000VAC to the secondary side, the electrical clearance is 5mm, the creepage distance is 8mm. ③ Output to PE, 500VDC (floating), electrical clearance 2.5mm, creepage distance 4mm.

  3. Requirements for ultra-low leakage current:

Low leakage current is the core indicator of medical power supply, IEC requirements for medical equipment under normal state test 264VAC, 50Hz, leakage current ≤500uA, but medical equipment is usually far more than one isolated power supply, some large CT will even have 5 or more power supplies. Therefore, for power supply manufacturers, the leakage current of a power module is best to be less than 100uA. For post-grade DCDC power supplies in contact with the human body, because of direct contact with the human body, the isolation requirements are more stringent, especially CF devices in contact with the heart, and the medical certification clearly requires ≤10uA.

  4. Requirements for ground continuity:

The reason why the medical power supply has requirements for this indicator is mainly because when the ground resistance is large, it is easy to lead to the ground potential difference of the equipment powered by different power supplies, which may be harmful to seriously ill patients, so the ground continuity must also be strictly tested, IEC requires PE to the resistance of any accessible metal at the shell <0.1Ω.

  5. Other requirements: In addition to the above routine requirements, medical equipment also needs to meet all the requirements of conventional civilian appliances, such as the need to meet the requirements of ROHS, the temperature that can be reached by the human hand must meet the requirements of conventional standards, etc., not listed in detail.