Diagram of leakage current in a power supply.

Leakage Current in Power Supplies

Guard Against Electric Shock

When designing a PC-based medical device, you need reliable energy source that won’t shock patients. Minimizing leakage current, a leading potential cause of shock hazard, is an important part your device design and vitally important in medical power supplies.

At all times you should avoid shock hazards in your designs, but it’s most important with medical devices. They could be near or touching patients, who are already vulnerable from existing medical conditions and may not be mobile enough or aware enough to move away from the source of an electric shock.

In PC-based medical devices, the power supply is one of the primary places to reduce leakage current, which is a common cause of shock hazard. As covered in the previous post, there are three types of leakage current in medical devices — earth, touch, and patient. Patient leakage current is mitigated by the device enclosure, which encases the power supply. Power supply design is therefore focused on minimizing earth and touch leakage current.

 

What causes leakage current in power supplies?

Leakage current can be found in any electrical device or system that’s run by AC power, including a PC-based power supply (a PSU). The unwanted current could come from several sources, but the most common path is through the Y class EMI filter capacitors to ground.

 

A trade-off between leakage and EMI

While Y capacitors are often the cause of leakage current in a power supply. They are used to mitigate EMI, but they can hold a charge. Increase the capacitance and you raise the amount of leakage current while lowering the EMI or vice versa. Since neither leakage current nor EMI is desirable and both are regulated in medical device standards, it’s a balancing act to mitigate them both to the proper degree.

 

What is EMI?

Electromagnetic interference (EMI) is electrical noise, an unwanted byproduct when switching currents and voltages. It’s unavoidable in a switching power supply and it can cause problems with other devices by interfering with electrical signals. EMI filtering is needed and usually done using Y class safety capacitors.

 

What are Y Capacitors?

Y class safety capacitors (also called Y capacitors) are a type of capacitor that are used to suppress the EMI generated by the power supply. They are placed between the AC line and ground on the primary side of the power supply.

 

How Do Commercial and Medical Power Supplies Differ?

All power supplies provide safety features, but medical-grade power supplies must meet rigorous Means of Protection (MOP) standards for earth and touch leakage current, to protect vulnerable patients. Commercial-grade power supplies can have up to twenty times the leakage current as those certified as medical grade.

When designing a PC-based medical device, you need reliable energy source that won’t shock patients. Minimizing leakage current, a leading potential cause of shock hazard, is an important part your device design and vitally important in medical power supplies.

 

For further information, please see our articles “Medical-Grade Power Supplies: Safety and Reliability Set Them Apart” and “Electrical Safety in PC Based Medical Products” or contact us.

 

(Leakage Current in Medical Devices,   Leakage Current in Power Supplies,   Leakage Current Requirements for Medical Power Supplies)

________________________

RAM Technologies power supplies are designed to meet medical device requirements, keeping both SFC leakage current and conducted noise to a minimum and meeting 2XMOPP patient protection standards.

 

 

Subscribe to the RAM Technologies Blog

Get the latest posts in your email
This field is for validation purposes and should be left unchanged.