Medical power supply selection and application

I. Introduction

In today's society, with the continuous advancement of science and technology, more and more modern medical devices have developed rapidly, especially electronic instruments that are in direct contact with the human body, in addition to the increasingly high requirements for the performance of the instrument itself. There are more and more concerns about human safety, such as: cardiac puncture monitors, ultrasound, maternal and child monitors, baby incubators, life monitors, etc., which are in close contact with the human body, that is, patients use The instrument should not cause any electric shock or other danger to the human body due to the use of the instrument.

Second, the choice of medical power

Medical electronics, unlike other electronic and power electronics that target mass-market and cost-conscious consumer electronics and other low-cost products, 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 system power supply section is: Is the purchase or manufacturing related solution?

Since medical electronics production is generally relatively low, designers must consider buying or making problems. Medical electronics designers rarely consider designing their own offline power supplies. Because the investment required for this particular design and test does not match the final production scale; equipment manufacturers will find it difficult or impossible to share the investment in the design phase. Therefore, it is more cost-effective to purchase power directly from companies that already have the corresponding professional design capabilities and testing techniques.

Price

In commercial application design, if the quality is guaranteed, it is easy for people to directly select the lowest-priced power product after shopping for three. At this time, the products with the lowest price but “going to go” are often winners, while the best products are not welcome. This is not bad for disposable electronic products that are quickly abandoned or need not be repaired, but what if the designer chooses such a power supply to use the medical system? The value of medical electronics is high and some key tasks need to be accomplished. If the medical system fails, the consequences are not just to miss a game or to take the wrong car. The proper functioning of vital medical equipment, especially power supplies for medical devices must comply with safety regulations, leakage, EMI-RFI radiation and protection aspects. These standards and related safety regulations constitute a set of strict regulatory requirements. Power supplies used in such demanding applications must meet stringent specifications for insulation measures to prevent patient and medical personnel from getting an electric shock. EMC is also a key issue, including how to reduce electromagnetic radiation and how to protect electromagnetic radiation. Therefore, for the design of medical power supply , the first choice must be the quality and reliability of the product.

Often, designers are confused about commercial power supplies and medical power supplies, and manufacturers that manufacture 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 choice of such power products will lead to terrible consequences. Therefore, designers need to understand the relevant regulations and regulations. So, what are the problems involved in choosing a medical power supply? The power supply for medical equipment must comply with safety, leakage, EMI-RFI radiation and protection regulations. Other issues, such as whether it is produced by a GMP-certified factory?

2. GMP qualification

The US Food and Drug Administration (FDA) requires medical products to be manufactured in factories that are GMP-qualified (ie, have good practices). This is a set of quality certification system that should be required by the manufacturer in addition to the traditional ISO9000 certification to prove that its quality control procedures comply with GMP regulations. Similarly, China also has strict control over medical power sources, such as CE and UL medical certification.

The GMP specification stipulates that manufacturers must have component quality control procedures and have relevant documentation. When selecting a medical power supply, can you ask the manufacturer to have a component quality control procedure? Are there quality data and test files? Ask what is the procedure and ask for the relevant documents. Manufacturers are required to produce documents that demonstrate the quality and reliability of their products, and reputable manufacturers will be happy to provide them. We have found that many low-cost manufacturers are using unbranded, un-manufactured power products or counterfeit power products, which poses many problems for the final medical electronics OEM. If the manufacturer can't come up with the relevant certification documents, and they just change the power of the POS terminal and then sell the medical power, then such a product will only make the user lose more than it. Therefore, for a good medical power supply choice, GMP qualification can prove its product production and quality control accordingly, but is such a product a good product? No, we must also grasp the performance parameters and reliability of the product, that is, whether the product has passed some international general specifications.

EN60950 is an international safety specification for general purpose power supplies. Medical power supplies also need to meet the minimum basic requirements of this specification. However, the international safety regulations for medical power supplies are more stringent IEC601-1 A2, and there are three versions by region: EN60601-1 in Europe, UL2601-1 in the US, and CSA22.2 No 601.1 in Canada.

These specifications cover technical indicators for electric shock protection, fire protection and machinery, as well as creepage distances and clearances, as well as test indicators for high-voltage insulation. Medical power supplies must be designed with appropriate design techniques to ensure stable operation when input is abnormal and to operate under certain environmental conditions such as oxygen and/or anesthetic gases. Fire protection is also an important issue in these applications.

3. Leakage current

Leakage current is the current that flows through the protective earth conductor to ground. In the absence of grounding, if a conductive path (such as a human body) is present, the current can flow from the surface of the conductive or non-conductive component to the ground. There is always an external current in the safety ground conductor. Generally, the upper limit of the leakage current of a medical power source is one tenth of that of a normal power source.

All power supply leakage current specifications of the IEC601 standard are much stricter than non-medical power supplies. The technical indicators define several different and most critical leakage currents, such as: earth leakage current (flowing into the ground along the grounding body) and casing leakage current (through the patient from the casing into the ground). The maximum leakage current of the three main types of equipment power supplies is defined differently in the IEC601 standard:

Class B: Equipment that does not come into contact with the patient's body, such as a laser therapy device.

Class BF: Equipment to be in contact with the patient's body, such as ultrasound, various monitors (including EGC equipment), and operating tables.

CF: A device that is in contact with the patient's heart, such as a cardiac puncture monitor.