Select medical power supply needs to pay attention to?

Today's society, with science and technology progresses, more and more modern medical equipment have been booming, especially in contact directly with the human body with electronic devices, in addition to the performance of the instrument itself increasingly high demands from the outside, on human safety considerations are more and more attention, for example: cardiac puncture monitor, ultrasonic, mother and baby monitors, baby thermal insulation system, and so on some life monitor in close contact with the human body, which means that patients use instrument instruments cannot use the instruments and on the human body caused a risk of electric shock or other aspects of any danger. Then, he was elected with the most relevant medical power supply, we should pay attention to?

Medical power of choice

Medical electronics, and other positioning in the mass market and care about the cost of consumer electronics and other low-priced products in the field of electronics and power electronics, medical electronics to abide by the rules.

If the designer is responsible for the system power design for system power supply part of the first to consider the question: buy or manufacture for solutions?

As a general medical electronic output is relatively low, the designer must consider buying or self-made.

Medical electronics designers rarely consider their own design offline power supply. Because this kind of special design and test the required investment and ultimately does not match the scale of output; device manufacturers will find product production is difficult or impossible to apportion the investment during the design phase. Therefore, to have appropriate professional design and testing technology company in direct purchasing power and more cost-effective.

1. the price

In the commercial application of design, if the quality assured, it's easy to shop around to select the price directly after the lowest power products.

This time, the price is the minimum but the "decent" products tend to be a winner, and the best products are not welcome. This is for those who will soon be abandoned or not need maintenance, one-time electronic product is nothing, but if designers pick one such power to use medical system will have any risk? medical e-value is very high, you need to complete some of the key tasks. If the health care system fails, the consequences of not just missed a game or on the wrong train. The proper functioning of the medical device and death, especially medical equipment of power supply, must meet safety, leakage, EMI-RFI radiation and the relevant provisions of the terms of protection. These standards and related safety specifications constitute a set of strict regulatory requirements. For such demanding applications in power in insulation measures must comply with the strict specifications in order to prevent electric shock patients and medical staff. EMC is also a key issue, including how to reduce electromagnetic radiation and how the two aspects of protection from electromagnetic radiation. Therefore, the design of medical power supply, the preferred must be the product quality and reliability.

Often, designers of commercial power supply and power supply for medical and confusing for mass market manufacture of various low power of the manufacturers may apply these commercial power does not change as a medical supply sales.

In this regard, the purchaser must be careful, because just for the sake of cheap and select such power products will lead to terrible consequences. Therefore, designers need to understand relevant provisions and regulations. Then, select the medical power supply will relate to which problems?, medical devices must meet safety, leakage, EMI-RFI radiation and the relevant provisions of the terms of protection. There are also other problems, including whether by GMP certification of factory production products?

2.GMP qualifications

United States food and Drug Administration (FDA) requirements for medical product must be obtained GMP qualified (that is, with good job specifications) of factory production.

This is in addition to the traditional ISO9000 certification should require manufacturers to produce a quality certification system, to prove its quality control procedures in line with GMP standard. Similarly, China also has medical power of strict control, for example, must conform to CE, UL, and a series of medical certification requirements.

GMP norms requiring manufacturers must have the parts quality control procedures, and related documentation.

Select medical power supply, you can ask the manufacturers have parts quality control procedure? quality data and test files? may ask what program to produce relevant documents. Requirements for manufacturers to produce can prove their product quality and reliability of file, reputable manufacturers will be pleased to provide. We found that many low-cost manufacturers are using no marks, no manufacturers of power products or counterfeit power product, to the end of medical electronics OEM brings a lot of problems. If the manufacturer cannot take out the authentication file, but they only POS terminal power transformed when medical power sales, then, this product will only make the users to gain. Therefore, a good selection of medical supplies, GMP qualifications can appropriate proof of the production and quality control, but this product is good product? no, we also have on product performance parameters and reliability to grasp that the product has adopted a number of international standard.

EN60950 is applicable to the general power to meet international security standards.

Medical power supply also needs to meet the specification of the minimum basic requirements. But the medical power of international safety norms are stricter IEC601-1 A2 and press area has three versions: Europe is EN60601-1, UL2601-1 is the United States and Canada is No 601.1 CSA22.2.

These specifications cover electric shock protection, fire and mechanical aspects of the specification and creepage distance and clearance, as well as high-voltage insulation etc test indicators.

Medical supplies must adopt appropriate design technology to ensure that the input when the exception is still stable work, and in some special (where oxygen and/or anesthetic gases) of the environmental conditions. In these applications, the fire is also a key issue.

3. leakage current

Leakage current is a protective earthing conductors of electric current to flow.

Without grounding conditions, if anyConductive paths (such as the human body) exists, the current available from conductive parts or non-conductive parts of the surface to ground. Safety grounding conductor always exist outside current. Typically, a medical power of leakage current limit is one-tenth of the normal power supply.

IEC601 standard all power leakage current indicators than non-strict medical power supplies.

Which the specification defines several different and most critical of leakage current such as: on the floor drain current (flow along the grounding) and shell leakage current (through patient flow from the shell). Standard for the following IEC601, three main types of device power supply maximum leakage current for a different definition:

B class: no physical contact with the patient's device, such as laser treatment instrument.

BF: physical contact with the patient, such as ultrasonic devices, monitors (including EGC devices), as well as the operating table. CF: contact with the patients ' heart of devices, such as cardiac puncture monitor.

People often misunderstand that the device type of leakage current indicators.

In fact, these types of devices allow the leakage current is the same. North American index requirements than European EN60601-1 provisions allow leakage current tighter. For example, Europe and the United States allowed 0.5mA, and Canada only allow 0.3mA. Thus, medical devices, designers need to note that its products will be sold to which regions.

And BF or CF class of device (commonly known as "contact with the human body" equipment) also require additional insulation measures so that patients and, signal ports and power output insulation.

This is for the equipment to an unexpected failure protection of patients, and for the patients of the leakage current in within the limits of the standard requirements. This insulation is also available through other parts of the final equipment, if there is sufficient insulation performance of plastic probe or casing. But the need for patient power applications, the processing methods used is consistent with the IEC601-1 standard AC/DC power supply on one or more isolated DC/DC converter power supply, i.e. added secondary insulation protection. Therefore necessary to carefully select DC/DC converter, to ensure that insulation requirements.

Due to medical devices often have to connect directly with the patient, but also through the skin or subcutaneous conduction pathway junction formation, the leakage current must as far as possible to zero, the insulation must be reliable, and shall not be prowling around current.

4. Security and isolation

Security and isolation is also a commercial power and a major medical power supply, the treatment of patients and medical staff using the device of electric shock and other security related.

Although the human skin is a good insulator, but once you have a very small AC current applied to heart, it is possible to cause cardiac muscle fibrillation and neuromuscular injuries. It involves the patient's environment equipment, any potential contact with patients of part of its current must be strictly limited in 40-70Hz.

Medical applications of the desired protection level and devices, and how closely related the patient.

Power supply for medical systems, insulation and protection index has three security levels. First, all offline power supply must meet the basic standard in EN60950 safety requirements. In addition, close to the patient's medical power supply must comply with the IEC601-1 standard. But contact with a patient's device in addition to meeting the above two requirements, but also need additional isolation barrier to protect. There are also commercial power outage, a standby generator to hospital for a few seconds or several minutes after the power supply. Therefore, many medical power supply and use of this power supply devices are powered through the UPS system to relay. Thus, the power of the input waveform may change, no longer is the ideal of a sine wave. So, you also need an external power front-end a medical transformer to further increase the security level. Therefore, directly to the patient's device must meet all of these parameters, the maximum insulation specification.

5.

EMI-RFI radiation and protection

Equipment of electromagnetic radiation and electromagnetic radiation protection is also an important medical power supply parameter standard involves a power surge and transient current strength, electrostatic discharge (ESD) level, and radio frequency interference (RFI) protection capability.

On medical power supply, these electrical indicators must be the same level of commercial products. Many medical applications involving RF apparatus or non-invasive electronic surgical instruments, so the power supply must be protected against interference, are not affected. Qualified medical power supply shall comply with EMC-related technical requirements of the many compatible EN60601-1-2 standard. Moreover, the medical power supply also must meet IEC61000-4-2 ((electrostatic protection capacity requirements meet 3kV), IEC61000-4-3 (radiofrequency radiation protection capabilities to 3V/m), IEC61000-4-4 EFT (voltage transient capacity requirements meet 1kV), IEC61000-4-5 (AC surge capacity to 1kV and 2kV), IEC61000-3-2 (power line harmonics), IEC61000-3-3 (power line flicker requirements), as well as EN55011 (A type of product or B product emission limits) and other requirements. To this end, consistent with the IEC601-1 standard power generally complies with EN55022/11A class equipment specifications, rather than a more rigorous class b EMC specifications. These devices can also be designed to meet class b EMC specification, but required additional more complex filtering and screening measures, making the device size increases, costs increase. Kim Seung Yang company Guangzhou medical power supply module in product size, cost, performance, security, and so made a very good balance.

There are also other, related to specific applications: If the system you might want to use in the ambulance car, voltage shock occurs, the power supply shall comply with IEC 68-2-29; some devices is a portable device, you may use in helicopters, random vibration, the power supply shall meet the standard MIL-STD-810E.

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Example: a customer uses a low-cost ", the" medical power supply voltage of 5V, 200mA, hundreds of current batch of unit price is $ 5.

Use the power of the device you want to sell tens of thousands of dollars. The price is low power seems amazingly good, if it's good to be skeptical, really. Apart of this power is found, it is only a single sided printed circuit board, and to save costs, circuit board hole without metallization. Circuit boards using surface mounting structure and component density. Component spacing does not meet the medical power supply and the relevant security authorities require Creepage distance requirements and design guidelines. Leakage current da 900mA, far exceeding the specification limits. Creepage distance and clearance voltage indicators has not yet reached a common power supply voltage in use. The spacing between the high pressure zone only 0.5 mm with solder resist to improve point media. Power MOSFET's pin spacing should be intensified in order to increase the Creepage distance, but this kind of power supply and fails to do so, most likely because considering manufacturing costs and doing so will occupy more space. Aluminum heatsink fastener through some claw into the circuit board, and then welded fixed. Once processing is not correct, the heatsink prone to loose. Flyback circuits of the MOSFET is no manufacturers of fullpak package devices, there is a silicone jacket and insulation tape on the heat sink, thus hampering the device and the heat sink, such use will likely have a serious thermal stability problem, that is, when the MOSFET is, the heat sink or cold. This kind of power supply just to satisfy business requirements, but EMI-RFI does not comply with the requirements of medical power supply.

This power also exists in other issues such as the entire power within existing virtual welding everywhere.

When used, even if they are properly assembled and maybe some will come out of the failure. This kind of power, though they are treated as medical supply sales, but it was never designed in accordance with the medical requirements, in addition to the input voltage and output voltage and current, there is no related documents and technical indicators. This kind of power in addition to the amazing low prices, the level of performance requires far less medical power supply requirements. Why some people just want the power cost reduced to such a level, but deliberately take so many risks? "after all, the power supply is high temperature, high pressure and noise, leakage current, fire and other risks and dangers of primary origin.

Therefore, in the selection and purchase of medical supplies, taking into account the relevant risk must be reputable, and can provide in conformity with the relevant standards of proof, and comply with quality and reliability standards and requirements of manufacturers.

Typical applications of medical power supplies

By understanding the medical power supply options, here we talk about a medical power of some typical application:

1. application of ECG test circuit: the following is a common type of ECG detection circuit, as Figure 1

Figure 1: a common type of ECG test circuit

As figure, this circuit is composed with INA115 ISO122 human ECG test circuit fully meet the requirements for medical devices, i.e. input impedance, low leakage current is small, high measuring accuracy and human body safety indicators; output signal isolation by ISO122 is transferred to the rear of the amplifier circuit, the realization of the human body signal and output and the power of isolation amplifier, use of isolated DC-DC module power supply can effectively non-inhibitory surroundings right and of EMI and eliminates ground loops, etc.

2. the patient's ECG monitoring circuit following the patient ECG monitoring circuit, Figure 2

Figure 2: the patient ECG monitoring circuit

As figure, this circuit is 3652 in patients in the ECG monitoring system for the application, this circuit is a balanced input connection, its common and differential mode input impedance is high, can greatly decrease in guardianship equipment often encountered in the imbalances lead impedance interference caused by a problem of common-mode noise interference; due to the use of DC/DC converter G1515S-1W, 3652 and patients touch of Earth and the input power cord really isolate, moreover, 3652 in input and output isolation voltage between allow continuous, allowing for 2000V isolated non-periodic pulse voltage up to 5000V, this makes it possible to protect patient safety.

The current market medical power supply module, which was mixed medical electronic industry belongs to a particular profession, for its very high power requirements, in order to guarantee the security of human and equipment performance, select medical power supply module is particularly important.

Out of the main describes medical power supply module main performance index requirements and medical power supply module in the medical electronics industry for some typical applications and considerations, hope this article gives a broad medical electronics designers select medical power when the power is able to bring the appropriate help.