The innovation of health care equipment requires more attention to safety, and the degree of attention is no less than the electronic equipment used in hospitals. Safety includes many aspects and requires electrical safety, so when connected to non-medical communication equipment or other household appliances, high voltage or leakage current will not flow into the human body. Electrical safety is largely ensured by isolation. Isolate and block the electrical path from the main power supply or other medical equipment (such as defibrillators and other high-voltage generating equipment) to the power supply of the equipment.
The main source of unexpected signals in electronic equipment is the power grid. Medical applications must be able to block AC leakage on 50 Hz to 60 Hz lines, transients caused by lightning strikes, switching noise, and line fault conditions. This is not just for medical equipment; however, medical equipment has stricter requirements in this regard, and the level of leakage depends on how the equipment is connected to the patient.
The connection between the device and the patient must also be isolated, to prevent the patient from using multiple medical devices, the device uses other connections as another circuit, resulting in unexpected current trends. In addition, if the patient can access any device connected to the building's safety ground (such as a home appliance or a metal bed frame), the current must not pass that path. Insulation for patients requires the use of two independent insulation systems, or a single system that has proven to be equivalent to two systems. This is called double patient protection isolation.
Typical home healthcare electronic equipment needs to communicate with other medical equipment or existing home electronic facilities. It must be able to meet privacy and security requirements and ensure that information is not intercepted or destroyed. It should meet the leakage and safety requirements in the IEC60601 specification. Usually the electrical connection needs to provide double patient protection, with a rated withstand voltage of 4kV and extremely low capacitive leakage and anti-defibrillation rated performance.
The most reliable way to achieve communication is to use a wired isolation interface. It has the stability of a wired interface; it can also provide power through a built-in isolated DC-DC converter. It supports high-speed upload and download, and can be used while the device is connected to the patient. The wired interface does not require data encryption, reducing processor overhead. Software maintenance can also be done while the equipment is working. The interface can also be set to achieve real-time remote monitoring at high data rates. For example, when a patient needs regular follow-up, a doctor can remotely obtain ECG. The isolation of these interfaces traditionally relies on devices such as optocouplers, which have speed limitations and poor integration capabilities. In new applications, medical-grade digital isolators are replacing optocouplers, and these limitations do not exist.
The defibrillator in Figure 1 has several different interfaces and uses a variety of isolation techniques, so it is an excellent example of checking isolated communication interfaces. The device must use ECG to monitor the patient's cardiac activity in order to decide whether to perform defibrillation. The ECG data path must be isolated from the high-voltage part of the defibrillator so that sensitive ECG electronics will not be fused when an electrical shock is applied to the patient. The isolation can be achieved internally by an isolated gate driver and a digital isolator. The device can also integrate an Ethernet interface for status monitoring when the device is idle on the wall; Ethernet uses mechanical interlocking, so it cannot be used when the defibrillator is removed from the wall. Similarly, the battery charging system is also connected to the wall and interlocked. The last function that needs to be isolated is the communication port, which allows downloading ECG and defibrillation data for the doctor to view and analyze. This connection generally isolates the USB interface, so data can be obtained without disconnecting the device from the patient.