Power Converter Module Selection for Medical Equipment

When it comes to electronic medical equipment design there are many aspects to be considered but nothing is more important than the safety of the patient and the health care personnel attending to them. We examine the core requirements below –

Isolation, insulation and withstand voltage – Almost all medical equipment will have contact with people and because of this the requirement for protection from voltages and currents hazardous to health is paramount, these requirements are stated in IEC60601-1 edition 3.1. MORNSUN, a global power conversion manufacturer, has developed a range of AC/DC Converters and DC/DC Converters specifically for this market sector. The range includes single output AC/DC Converters of 5W, 15W and 25W, single & dual output DC/DC Converters of 1W, 2W and a single output 6W series.

The level of protection of a specific power converter is referred to in respect to MOOP (method of operator protection) and MOPP (method of patient protection). Isolation protection includes creepage/clearance distances, insulation, and protective earths. MORNSUN products use specifically designed PCB’s to ensure that they meet creepage and clearance requirements using a number of techniques that are needed to meet these specifications miniature power converters (Fig 1.).  Transformers are designed using tri-rated wire to provide multiple levels of insulation to the meet the requirement.

For medical equipment with direct patient connection there is a requirement for two levels of electrical safety. One level is to isolate the equipment from the 230VAC supply and the second is a DC/DC converter to provide isolation of the patient from the equipment in the event of a failure of the AC power supply. MORNSUN medical specification DC/DC Converters have 6KV DC (4.2KV AC) input to output insulation based on a 240V AC working input voltage, the 1W and 2W series products are rated at 1 x MOPP and 2 x MOOP and the 6W series is rated at 2 x MOPP. The AC/DC Converters are rated at 2 x MOPP.

Ultra-low leakage current – Low leakage current is a core principal of protection in medical electronics. The MORNSUN range of AC/DC Converters has a maximum leakage current of 80µA and the DC/DC Converters have a maximum patient leakage current of 2 µA.

Design Flexibility – In addition to safety concerns, medical equipment designers must also consider a host of other factors when choosing the best power supply for the application. Some of these specifications include input range, output voltage, power output, standby power, operating temperature and product warranties.

The MORNSUN range of AC/DC Converters offer a full universal input (85 – 264V AC) but can also accept a wide range DC input (100 – 370V DC). These products also standardize single outputs of 5V, 12V 15V and 24V. They feature no minimum load with high efficiency (89% max.) and low standby power consumption (0.1W max.) to meet current requirements.

The 1W and 2W DC/DC Converters are designed to have an input from a regulated source and offer inputs of 5V, 12V and 24V with standard single (3.3V, 5V, 12V and 15V) and dual (±5V, ±9V, ±12V and ±15V) outputs. The 6W series DC converters have an ultra-wide input range with 9-36V and 18-75V inputs available, which makes this series suitable for battery applications in addition to other standard applications.

Both the AC/DC Converters and the DC/DC Converters feature a wide operating temperature range (-40 to +85°C).

These products are specifically designed to ensure the excellent reliability required of critical medical systems. The latest SMD production techniques are used to ensure high manufacturing repeatability and this coupled with the highest quality components provides a minimum MTBF of 300K hr’s. Based on the quality approach used these products are provided with a 3 year warranty.

EMI – Medical devices need to meet the conducted and radiated emissions requirements of EN55011 and this is a challenge whilst providing low leakage and high isolation. MORNSUN converters are designed to meet Class A as a minimum.

The products featured in the MORNSUN medical series are compact and based on industry standard footprints and in addition to use in medical electronics they may be used in other applications where a requirement for high isolation and low leakage exists, such applications include electricity metering and monitoring, IGBT drivers and photo-voltaic control systems.