A common acknowledgment is “Medical DC power supply essentially that ITE power supplies plug in IEC 60601 certification.” In fact, it is wrong. And this acknowledgment seems like no problem in the early prototype stage, but in the system integration, certification testing, and actual clinical use phase will expose a series aisks that cannot be ignored. So this artical tell us why Medical DC power supplies are different from ITE power supplies in design logic.
Both of the different risks
Medical equipments risks model
Medical standards’ core assumptions include that the equipment may have direct or indirect contact with the human body; the user may be in an extremely vulnerable state; even if in a single fault condition, it cannot create unacceptable risks for the patient. These standards mean that the medical power supply design is not around the “normal work”, but around the “worst case”.
ITE equipments risks model
The ITE power supply design key points differ from those of the medical power supply. Its default users is health adult people, and the human is not a part in th equipment features. Moreover, the ITE power supply risks are contained in that the operator received an electric shock, fire, or property damage. But it doesn’t mean the ITE power supply is unsafe, as it safe target for different medical equipment.
IEC 60601 and IEC 62368 design logic
The IEC 60601 design logic assumes that errors are inevitable, components may fail, and equipment may work in disadvantageous conditions. Therefore, its standard requirement structure, isolation, leakage current, and reliable side are all reserved with a large margin.
Another, IEC 62368 uses Hazard-Based Safety Engineering[1]（HBSE）[1]ideas, which include identifying dangerous energy, reducing risks through protective measures, based on a reasonable foreseeable use way. These ideas suit the ITE equipment, but do not suit direct use for medical scenarios, as medical equipment is unacceptable due to the reasonable risks.
MOPP and MOOP are not as simple as just a few extra millimeters of distance.
In medical power supply, MOPP[2]（Means of Patient Protection）and MOOP[3]（Means of Operator Protection）offen simple understand “Higher level insulation.” In engineer side, it represents different reliable assumptions.
MOPP means that higher isolation requirements, stricter creepage and clearance requirements, and requirements for the long-term reliability of materials and protection capabilities must be maintained even in the event of a single failure. 2 x MOPP is not 2 x MOOP simple overlay; that reassessment for failure probability, aging path, and environmental impact.
The medical system constitute to power supply, a motherboard, a shell, and cables. If the power supply fails to fulfill its required MOPP responsibilities, the entire system will be forced to compensate using other modules, which not only increases design complexity but also significantly raises system risks.
Key electrical specifications: why more strict for medical equipment
The leakage current is not only a number but also a link. In a medical application, leakage current affects more than ITE equipment. Because a small current can creat effect to patient, the EMI suppression circuit’s Y capacitance direct effect leakage current, and after multiple modules are stacked together, the leakage current of the system may be more that single module test result. This means the power supply single test pass is not equal to the system pass.
The medical equipment usually lasts for 7-10 years or more. High temperature, humidity, cleaning, and disinfecting the environment speed up the material aging and reduce the initially perceived safety margin. ITE power supply is usually not designed for the long-term and strict environment.
ITE’s EMC is more attracted to not disturbing others. Medical’s EMC attracts to not disturbing self-sensitive module and not affect life support or monitoring functions. With the same power supply, the medical equipment will lead to some problems, but the ITE equipments not happen.
Why “functional” doesn’t necessarily mean “compliant”
In actual projects, some people think of using an ITE power supply instead of a medical DC power supply, but some common results include complete certification stage findings exceeding the standard of leakage current; single-fault testing is unable to pass; the system EMC problem is difficult to position; and the listing date is delayed. These problems happen in the projects later. At this time, you change the power supply, meaning that architectural adjustments are required, repeat the test, and the cost and time increase.
In medical equipment, the external DC power supply is easy to verify, and the core values are let high risks part outside of the system, clear system’s responsibility border. Of course, external doesn’t mean reducing the requirement for cable reliability, the plug misuse risk, and user replaceability. You need to carefully evaluate these requirement in system side.
So if you are an engineer need to ask the following problems:
What is the leakage current of the power supply in the system condition?
Does it support 2 x MOPP? Which section structure comes true?
Does it still meet the medical requirement in high temperature work?
Is the behavior predictable under a single fault condition?
These problems do not decide “if through test” but rather truly accept the engineering responsibility of medical equipment.
In all, medical DC power supplies different of ITE power supplies in price, volume, tag of certified. More in come from the risk module, design philosophy, and different understandings of the responsibilities of the system and the patient. In a medical application, the power supply selection is not for a thorough test, but in order to ensure the bad solution is still worth trusting.
[1]: Explore this link to understand the principles of HBSE and how
[2]: Understanding MOPP is crucial for ensuring patient safety in medical devices. Explore this link to learn more about its significance.
[3]: MOOP is essential for operator safety in medical environments. Discover more about its role and importance in this informative resource.
