Empowering Healthcare Devices Innovation: Creating Flexible System Monitoring Vital Signs

Medical devices must meet more stringent safety standards than office equipment and are classified into two categories:

Operators are considered to be healthy and well-trained. Equipment only in contact with operators must meet MOOP (means of operator protection) requirements. Typical examples would be IVDs (in-vitro-diagnostic devices)

Sick people are more susceptible to electrical shocks and devices connected to or in proximity to a patient must meet the more demanding MOPP (means of patient protection) requirements.

The following table and graphics show the MOPP classifications:

Overcoming Challenges in Navigating Electrical Isolation and Leakage Currents

Earth leakage currents, mainly generated by EMI filters in the AC power supply, are limited to 500µA, enclosure leakage currents must not exceed 100µA. With earth leakage currents below 100µA both values are easily met by all P-DUKE AC/DC power solutions.

Patient leakage currents depend on the type of application and vary between 100µA and 10µA, a topic covered in another case study.
 

Successful Portable Patient Monitoring Project:

To make patient transport easier, a customer designed a modular patient monitor consisting of a base station and small plug-in modules for different monitoring cases. For transport, the modules are pulled out of the base station and placed on the patient’s bed while continuing to monitor vital signs. When plugged into a base station again, data are uploaded into the base station and the hospital information system.
 

Power Solution for the Base Unit:

The base station needs 20W and the plug-in modules maximum 7W. The 10.8V Li-Ion batteries provide up to 6 hours of backup time and then must be recharged in 6 hours. Considering internal losses, the maximum power consumed by the device is around 60W. P-DUKE´s MED100 AC/DC product with a 15V/100W output offers sufficient power margin, is 2xMOPP compliant, and has a Class B EMI filter with only 75µA earth leakage current.

When connected to mains, the voltage on the internal bus is 15V. In battery backup mode it can drop down to 9V when batteries are more than 90% discharged. Therefore, the downstream converters must cover a 9 – 15V input range.

Data processing and the touch screen need 5V with in total 15W. Although only operators should touch the screen, patients can get in contact with the screen, too. Therefore, a 2xMOPP compliant 20W converter from the MPM20 family with 5000Vac isolation voltage and 8mm clearance & creepage was selected.

From this 5V bus, a non-isolated converter from the HSRP6 family generates the 3.3V supply voltage for the internal WLAN module.

The isolated LAN interface is connected to the hospital network. Wiring or connection errors and isolation failures within other devices in the network may void the safety concept of the system. Therefore, the customer added an additional 2xMOPP compliant isolation barrier by using a low-power converter from the MPL02 family.

Base unit solution:

Power Solution for the Plug-in Modules:

Customers can choose between various configurations, each requiring 2xMOPP compliant supply voltages for sensors and the touch display. The solution was to generate a 2xMOPP compliant bus voltage of 5V by using a 10W MPP10 module.

Data processing, the display and all 5V patient sensors can be supplied directly from this bus. If other voltages or isolation for noise-sensitive sensors are required, P-DUKE offers one of the largest ranges of isolated and non-isolated modules providing single positive and negative or dual output voltages from 3.3 up to 24V.

DC/DC converters plug-in modules solution:

Another target was keeping the total weight under 3.5kg. With just 270g, the power supply contributes less than 8%.
No audible noise and therefore no fans are allowed. All these highly efficient converters can work with natural convection only and don’t need additional heatsinks which keeps total weight low, too.

Weight calculation of a typical configuration:

Striking the Balance Between Efficiency and Weight: The Specific Needs of Patient Monitoring Devices

This design required a complex, lightweight power solution with different converters working seamlessly together and providing the necessary isolation barriers. Based on P-DUKE’s very wide range of AC/DC and DC/DC converters a complete solution was found to solve all the challenges in this application.