The medical power supply has special considerations for safety and has its particularity. The following describes the leakage current and protection level.

1. Leakage current

The isolated power module serves as the main isolation component of the entire medical system, and it will also greatly affect the leakage current of the entire system. Therefore, for the leakage current required by medical equipment, the power supply module must be satisfied as much as possible, and the design of the system to ground must also be considered. It is best to leave a margin for the leakage current.

(1) Different medical equipment has different requirements for leakage current and protection level

At present, the latest third edition of the medical certification IEC60601-1-3rd, according to the application part, the medical equipment is divided into three categories: category B, BF category and CF category, as follows:

Class B: The lowest level of patient protection among all types of applications, such as devices that do not come into contact with the patient's body, such as laser therapy equipment.

Class BF: a higher level of patient protection than Type B applications, equipment to be in contact with the patient's body, such as ultrasound, various monitors (including EGC equipment), and operating tables.

Class CF: The highest level of patient protection, suitable for direct cardiac applications, such as cardiac puncture monitors.

(2) Classification and requirements of leakage current

For medical devices, the leakage current can be divided into patient leakage current, patient auxiliary leakage current, accessible leakage current, and ground leakage current according to the application of the device.

Patient leakage current refers to the current that flows into the ground through the patient and the F-type application when an external voltage is applied. During actual testing, an MD module is connected in series in the loop to simulate the impedance of the human body.

Patient-assisted leakage current refers to the current that flows from patient A to patient B through the device through the device.

The contactable leakage current refers to the leakage current between the human body and the accessible point. It is usually required to be 100uA in normal state and 500uA in single fault state. Normally, the leakage current between the MD module and the ground, and the shell that is not protected by the ground is measured during the test.

The ground leakage current refers to the current of the equipment to ground, the requirement is 5mA, and it is 10mA in a single fault state.

In the above leakage current test, the voltage tested in the medical certification requirements is mostly at 110% of the rated grid voltage, which means that it is not the definition of leakage current that we conventionally understand. Generally, the network voltage range of medical equipment is 100-250VAC. According to the worst conditions, the test should be 265VAC, 60Hz. Therefore, when the demand for medical power is raised, it is also necessary to focus on the customer's test conditions.

2. Protection level

The protection level refers to the specification requirements for the protection strength of different medical equipment. The medical device operator is a doctor, and the target is the patient. In the third edition of IEC60601-1, the protection levels are divided into MOOP (Means of Operator Protection) and MOPP (Means of Patient Protection). Different protection levels correspond to different pressure test requirements, usually 1*MOOP, 2*MOOP, 1*MOPP, 2*MOPP as requirements. The pressure resistance requirement of MOPP protection is higher than that of MOOP. The working voltage of medical equipment is usually 250VAC. To meet the protection requirements of 2 MOPPs, the withstand voltage of 4000VAC is the basic requirement.