Medical Grade Power Supply for Type BF Medical Applications
By Kai Li/MEAN WELL USA
Introduction
Research has shown that even a small amount of current flow through the human heart can lead to serious consequences such as ventricular fibrillation. Medical patients’ weakened bodies are even more susceptible to electrical harm. Therefore, it is important for Medical Electronic Devices to undergo stringent electrical safety tests as outlined by IEC 60601-1 3th edition and its harmonized equivalents for different countries around the world. For medical grade power supplies, it is critical to ensure the leakage current and isolation levels can meet the specified limits of the corresponding Applied Parts type of the medical application.
Applied Parts (AP) are classified into three types: Body (B), Body Floating (BF), and Cardiac Floating (CF). Type CF is the most stringent classification, which is for Applied Parts that may come into contact with the heart, such as surgery equipment. Type B is the least stringent classification, which is for Applied Parts that are normally not conductive, such as hospital beds. For the purpose of this paper, we will focus on Type BF, which is used for Applied Parts that have long term or short term conductive contact with the patient. We are most interested in Type BF applications because Type BF is perhaps the most prevalent to the largest group of patients, covering Medical Electronic Devices from blood pressure monitors to non-cardiac surgical equipment. In this MEAN WELL white paper, we will discuss the leakage current and insulation requirements of power supply for Type BF medical application, as well as examining a case study of MEAN WELL’s medical grade power supply to demonstrate the considerations for medical compliance testing.
Leakage current sources can be categorized into Earth Leakage, Enclosure Leakage, and Patient Leakage. Patient Leakage is specified for each type of Applied Parts, but the patient leakage is only considered for the end system. The outputs of power supplies should never be connected directly to a patient as part of the Applied Parts, so only Earth and Enclosure Leakage currents are tested for compliance.
The leakage current limit for each source as defined by IEC 60601-1 3th edition is indicated in Table 1.
| Leakage Current | Type B | Type BF | Type CF | |||
| NC | SFC | NC | SFC | NC | SFC | |
| Earth Leakage | 5mA | 10mA | 5mA | 10mA | 5mA | 10mA |
| Enclosure Leakage | 100µA | 500µA | 100µA | 500µA | 100µA | 500µA |
| Patient Leakage | 100µA | 500µA | 100µA | 500µA | 10µA | 50µA |
In order to qualify a power supply for Type BF application per IEC 60601-1 3th edition, the Earth Leakage needs to be less than 5mA under normal conditions and cannot exceed 10mA under single fault conditions. Diagram A shows the circuit diagram for measuring Earth Leakage. The normal condition is defined as S1 closed and S5 normal or reversed. The single fault conditions are defined as S1 open and S5 normal or reversed.
Diagram A.
The Enclosure Leakage is also known as Touch Current, and Type BF applications for IEC 60601-1 3th edition requires the Enclosure Leakage current to be less than 100µA under normal conditions. Under single fault conditions, the leakage current cannot exceed 500µA. Diagram B shows the test circuit for Enclosure Leakage. The normal conditions are defined as S1 and S8 closed, and S5 normal or reversed. Single fault conditions are created by either S1 or S8 open, while S5 is terminated in a normal or reversed state.
Diagram B.
Isolation Level Considerations
In addition to leakage currents, isolation levels also need to be considered when qualifying a power supply for Type BF medical application. Table 2 shows the insulation requirements for I/P-O/P, I/P-FG, and O/P-FG.
| Type | Input to Output Isolation |
Input to Ground Isolation |
Output to Ground Isolation |
| B | 4000VAC (2 x MOPP) |
1500VAC (1 x MOPP) |
500VAC |
| BF/CF | 4000VAC (2 x MOPP) |
1500VAC (1 x MOPP) |
1500VAC (1 x MOPP) |
Type BF Rated Power Supply
We will examine the leakage current and isolation test results of the MEAN WELL RPS-400 series as a case study to see the compliance of a medical grade power supply to the IEC 60601-1 3th edition. The RPS-400 is a highly reliable and highly efficient open frame medical power supply that packs up to 400W power into a 5”x3” compact package, so it is a perfect example for next generation power supply that can be used inside Type BF medical applications.
Table 3 shows the measurements for Earth Leakage and Enclosure Leakage currents under normal and single fault conditions. The tests were carried out at the 264VAC/60Hz input to represent worst case scenario for leakage currents. Per results, the tested currents are much lower than the allowed current. This will help reduce resources needed to address leakage current issues when designing the end medical product.
Table 3
| Test Conditions | Allowed Current | Tested Current |
| ER; NC: S1=1, S5=0 or 1 | 5mA | 274µA |
| ER; SFC: S1=0, S5=0 or 1 | 10mA | 528µA |
| TC; NC: S1=1, S5=1 or 0, S7=1 | 100µA | 74.6µA |
| TC; SFC: S1=0, S5=1 or 0, S7=1 | 500µA | 122µA |
| TC; SFC: S1=1, S5=1 or 0, S7=0 | 500µA | 97.9µA |
The RPS-400 series has also been subjected to dielectric strength tests with the Type BF isolation voltages. The isolation level has been successfully evaluated to be suitable for Type BF applications with 2xMOPP from input to output and 1xMOPP from output to ground.
Summary
Due to the nature of medical applications, profound considerations are necessary for a fault-proof medical system that provides maximum protection for the patients. Hopefully, this white paper was able to provide some insight into leakage current and insulation requirements for Type BF medical applications and for why it is important for power supplies to meet all the stringent requirements outlined by medical safety standard such as the IEC 60601-1 3th edition.
MEAN WELL offers a wide variety of high-quality medical grade power supplies that can satisfy the customer’s Type BF medical power needs for both low power and high power applications. Please contact MEAN WELL authorized distributors or sale representatives for more information.