The term "medical devices" can encompass a wide range of technologies, from sensors placed on the skin or in the body to cauterization tools used during surgery. One thing they all have in common is the need for assured electrical safety in a small package. Engineers often use board-mount DC/DC converters in medical power supplies to provide proper isolation and prevent patients and operators from lethal electrical shocks.
We'll go over the electrical demands of medical devices, how AC/DC and DC/DC converters can help, and other things to keep in mind when designing a medical appliance.
Of course, medical devices are highly regulated by governments and standards development groups. These robust regulations are critical for protecting patients and operators — such as nurses and doctors — from experiencing lethal shocks. Some standards you'll likely need to meet include:
These standards usually outline technical requirements and any additional demands like risk analysis. Technical requirements generally include a double-safe electrical separation between any high energy sources or hazardous voltages and the patient or operator. These devices need two means of protection (MOP) — also called measures of protection — including means of operator protection (MOOP) and means of patient protection (MOPP). Of the two, MOPP is more stringent, since patients are more likely to be vulnerable and unable to handle the shock.
When using an AC/DC converter, isolation is always necessary. If the power supply fails, it protects patients from being shocked with lethal voltage. It also ensures patients can receive high voltage during some procedures, such as cauterization or defibrillation.
Medical devices have specific isolation requirements to ensure patient safety. AC/DC converters often have some type of isolation, but these mechanisms don't always meet the strict demands of medical devices. For instance, they might lack one means of protection or have a high isolation capacitance that doesn't meet low leakage current demands.
The applied part of a medical device is the part that contacts the patient. Isolation requirements vary by the type of applied part used. These include:
Although not always required for functionality, DC/DC converters in medical supplies may also need isolation in some situations, such as:
Although you can find AC/DC converters that meet medical standards, they are generally expensive. Combining AC/DC and DC/DC converters can provide a more affordable option.
One way to meet medical safety standards is by combining an AC/DC converter and a DC/DC converter in the right series. For example, you can follow an IT-grade AC/DC converter with an isolated, medically-approved DC/DC converter that delivers power to just the patient- or operator-accessible components. However, you would need to select the AC/DC converter carefully to ensure it meets the medical specifications, such as EMI suppression. If the leakage current for the AC/DC converter exceeds leakage current requirements, you could add additional EMI controls, for instance.
The primary benefit of opting for a DC/DC converter is that it adds an extra layer of protection between the patient and any equipment they're connected to. During the risk analysis process, you must consider the worst-case scenario of what happens when equipment fails. If not adequately isolated, the patient or operator could experience electrocution or burns. While the connections to a patient must be isolated from the ground, DC/DC adds another level of isolation between the patient or operator and an external signal fault condition.
For example, while it can be difficult to keep leakage levels within the required specifications on an AC/DC converter, DC/DC converters can easily accommodate low leakage currents. You could power the patient connection from a DC/DC converter that meets the right demands. You'll need to consider what types of connections you're working with and the style of grounding to choose adequate isolation technologies.
In general, meeting medical specifications, particularly 2MOP, through a DC/DC converter is generally more cost-effective than trying to do so through an AC/DC converter.
Isolation specifications are crucial, but you'll also need to consider how your medical appliance will meet other specifications, such as:
Astrodyne TDI is a leader in power solutions, with DC/DC power supplies perfectly suited to the medical industry's strict requirements. We've put over six decades of experience to work in providing reliable power delivery across a wide range of installations. We have ISO 9001 and ISO 13485 certifications, so you can be confident in the quality and consistency of Astrodyne TDI products.
Explore our DC/DC power supplies online, or reach out today to chat with an expert about your medical appliance.