Major Characteristics for Medical Power Supply

Medical environments are known for its omnipresent risk for both vulnerable and healthy people. To ensure the utmost safety, the design of Medical Power Supplies is monitored by the strictest quality exigences and safety regulations.

As the heart of any electrical medical device, the medical power supplies must comply with the highest standards of performance, safety (IEC 60601) and reliability. Criteria such as MOPP, MOOP, low leakage current, EMC must be taken into consideration during the development stage.

As a result, Medical Power Supplies are equipped with higher levels of insulation and superior EMC performance, and we can distinguish one medically approved Power Supply from other electronics components by its exigent protection level, its high reliability and its extended life cycle of components.

How to choose your Medical Power Supply?

As the keystone of one medical system, it is extremely important to select a safe and reliable Medical Power Supply. To choose the most suitable Medical Power Supply for the Medical system, the R&D engineers are strongly suggested to take, as guideline of selection, the listed criteria below into consideration

 

A. Electrical requirements

 

The input voltage range and required power should be defined for the application, as well as its output voltage and the needed current to power the application:

  • Input voltage range:  the most common input source is an AC source, and the range requirement is related to the destined market of the end devices. In the case of multiple market regions of the Medical system, it is strongly recommended to choose a Medical Power Supply with input voltage range covering at least the range of 100VAC to 240VAC.
  • Power requirement:  the required power depends mainly on the end device. It is suggested to keep in mind the derating caused by the unfavorable working temperature, as well as the potential peak current.

Output voltage and current:  according to the design of the Medical system, some systems demand a constant current output while others need constant voltage. The R&D engineers should choose an adequate Medical Power Supply, with the right level and type of DC output, based on the design of the application.

 

B. Regulations

 

As each market territory and each application field imposes its own safety regulations on the end devices, it is crucial to understand which certifications are mandatory for the application and its target market(s) during the development process.

For instance, home healthcare devices are required to meet the standards of IEC 60601-1-11, while for equipment not directly in contact with the patient, IEC 62368 might still give one the possibility to get a medical certification for medical test and measurement equipment on a system level.

Meanwhile, each country adopts its specific safety standards for the application field (e.g. UL ANSI/AAMI ES60601-1 for the US, EN 60601-1 for EU countries, CAN/CSA-C22 3rd edition for Canada…etc.

 

C. Installation Method

 

The installation of the PSU can be either internally or externally depending on how the Power Supply is designed to be integrated into the system.

External solution:

Internal solution:

  • Medical Enclosed type: PSU with plastic or metal case.
  • Medical PCB type: A PCB populated with components which from the power supply. Normally this solution is without any mechanical protection such as a housing. For this reason, normally installed inside an application and not touchable by the user.
  • Medical On board or Medical PCB mount: PSU designed to fit on a PCB. It can be either “open frame” or “encapsulated”. The second type is potted with compound to provide protection against external elements (e.g. moisture, corrosive elements, shock, vibration…etc.).

 

D. Other requirements

 

Medical systems are regulated with extremely vigorous exigences. On top of the above criteria, it is also important to verify that the other specific requirements are met:

  • Class: Class I or class II
  • Heat dissipation: Forced air cooling (with fan) or Passive cooling (without fan)
  • Level of protection required:  2 x MOOP, 2 x MOPP
  • Leakage current
  • Overload protection: Constant Current Limiting or Hiccup mode
  • Remote on/off function
  • Current sharing function
  • Parallel function

More Information about Medical products?

Specific Requirements for Medical Power Supplies

I. IEC 60601-1:

 

Defined by the world known International Electrotechnical Commission (IEC), IEC 60601-1 is a series of technical standards destined to ensure the safety and performance of electrical equipment in the medical industry. On one hand, some digression from the IEC 60601-1 standards exists. For example, EN 60601-1 for Europe and ES 60601-1 for the US market which are harmonized with the IEC standards. One the other hand, there are also some “collateral” standards to IEC 60601-1; such as IEC 60601-1-2 which is the 4th edition of collateral EMC standards to IEC 60601-1.

 

II. MOOP and MOPP 

 

In the medical environment, risk is constantly present for patient and/or operator of a medical device. Aiming to protect both groups from electrical medical devices, MOOP and MOPP are introduced to monitor the level of insulation.

  • MOOP stands for Means of Operator Protection. This category is related to electronic devices which are handled by trained operators, and do not come into direct contact with the patient. The medical device with 2 x MOOP has an isolation of 3000V AC isolation.
  • MOPP, on the other hand, is the Means of Patient Protection; all electronic devices with direct physical contact with patients must meet stricter standards and require a double isolation between input and output.

Presuming that patients are vulnerable; MOPP standards are specially designed to protect them from any potential electric shock. In the design, MOPP requires the medical devices to have two separate insulation barriers.

Therefore, devices are MOOP and MOPP classified depending on the type of contact with patients and operators.

Classification Required Isolation Required Creepage Requirement Insulation
MOOP 1500V AC 2.5mm
2 x MOOP 3000V AC 5mm Reinforced
MOPP 1500V AC 5mm
2 x MOPP 4000V AC 8mm Reinforced

1 MOOP and MOPP under IEC60601-1 are different in the levels of isolation, creepage, insulation.

III. Low leakage current

 

The essential use of medical equipment is on the human body, therefore the chance and duration of contact with this equipment is higher and longer. Having electric current running throughout the body can be extremely dangerous and might even result in death. For example, a current as low as 40mA could already be fatal to a healthy person, while a weakened person’s tolerance is even lower.

To protect all people in contact with the devices from the electric shock, medical power supplies must meet strict requirements in terms of leakage current. While Applied Parts (AP) indicate the parts of a Medical device or a Medical system which, during normal use, come into direct physical contact with a patient. The standards of IEC60601-1 give a clear definition of the acceptable values of leakage current for each classification of Applied Parts (AP), and the classifications are further divided into 2 categories: “NC” for normal condition and “SFC” for Single fault condition.


Leakage Current
Type B Type BF Type CF
NC SFC NC SFC NC SFC
Earth Leakage Current 5mA 10mA 5mA 10mA 5mA 10mA
Enclosure Leakage Current 100µA 500µA 100µA 500µA 100µA 500µA
Patient Leakage Current 100µA 500µA 100µA 500µA 10µA 50µA

2 Different Leakage Current limits defined by IEC60601-1 according to the medical environment: Type B, Type BF, Type CF

IV. Classification of medical environment

 

Just like medical power supplies, end systems in medical environments are also regulated by strict isolation and leakage current requirements.

Depending on the type of physical contact between patient and medical device, there are three main classification types of Applied Parts (AP) in the medical environment: Type B, Type BF, Type CF.

  • Type B (Body)
    Devices with no direct physical contact with patients. Examples: medical bed, medical laser…etc.
  • Type BF (Body Float)
    Devices with physical contact with patients and might present risk in the case of device failure. Examples: Incubators, diagnostic equipment, etc.
  • Type CF (Cardiac Float)
    Direct contact to the patient’s heart, risk of injury or death in the event of device failure. Examples: Defibrillators, heart-lung machines, etc.

Note: Medical power supplies for type BF & CF devices are designed to meet 2 x MOPP

V. EMC standard and limits

 

Malfunction induced by electromagnetic or interference could be fatal when it comes to life-saving devices. The EMC standards EN 55011 for electromagnetic interference and IEC 60601-1-2 with reference and electromagnetic immunity must be considered.

The 4th edition of the IEC-60601-1 standard on EMC is much more vigorous with electromagnetic immunity than the previous edition. Medical devices must now be immune to HF fields up to 2.7GHz, which represent an increase by 0.2GHz. To prevent damage caused by electrostatic discharge, the limits have also been increased accordingly. For contact discharge, the level has been increased from 6 to 8kV. For air discharge, it has been increased from 8 to 15kV compared to the previous edition.

 

VI. EU Medical Device regulation (MDR)

 

The European Union Medical Device Regulation (MDR) published 2017, will soon replace the current Medical Device Directive (MDD) (93/42/EEC) and the EU’s Directive on active implantable medical devices (90/385/EEC). All development engineers and manufacturers related to Medical Devices within Europe will need to follow the Medical Device Regulation of 2017 published by European Parliament.

 

VII. ISO 13485

 

ISO 13485 is the standard for the quality management system for medical devices. The requirements are destined to organizations involved in the design, production, storage, installation and maintenance of medical devices and other related services.

Got questions?

Look at the section below to find the most frequently asked questions (with answers)
we received in Medical Power Applications.

1. To increase the reliability of the power supply, we suggest users choose a unit that has a rating of 30% more power than actual need. For example, if the system needs a 100W source, we suggest that users choose a power supply with 130W of output power or more. By doing this, you can effectively boost the reliability of the power supply in your system.

2. We also need to consider about ambient temperature of the power supply and whether there is additional device for dissipating the heat. If the power supply is working in a high temperature environment, we need to make some derating to the output power. The derating curve of “ambient temperature” versus “output power” can be found on our specifications.

3. Choosing functions based on your application:

  • Protection function: Over Voltage Protection (OVP), Over Temperature Protection (OVP), Overload Protection (OLP), and etc.
  • Application function: Signaling Function (Power Good, Power Fail), Remote Control, Remote Sensing, and etc.
  • Special function: Power Factor Correction (PFC), Uninterruptible Power Supply (UPS) function.

4. Make sure that the model qualifies for the safety standards and EMC regulations you need.

Categories: Industrial, Medical, Others

Capacitive loads can be found under many different forms: capacitor banks, batteries, and even power supplies themselves are considered as capacitive loads. The principal issue that can appear on such type of load is at PSU start-up: a discharged capacitor basically acts like a short-circuit at start-up, hence it may overload the output.

One solution is either to add current limiting resistors in series with the capacitive load to limit the output current, or to select a power supply with “constant current limiting” overload protection type. This way, the power supply will automatically limit the current to a certain level stated in the specifications:

SPV-150 series specifications

For inductive loads, motors need high current at start-up, therefore a power supply with peak power capability is recommended (or a PSU with constant current limiting overload protection type).

The main issue of dynamic loads is output voltage drop. If the load step is too high in amplitude and too long, it may be able to completely discharge the output capacitors and then create a voltage drop or high ripple at the output. If the frequency of the load changes is high enough, this kind of issue is less likely to happen (please refer to the test reports for more information). One solution could be to put additional capacitors between Power Supply and load.

Some applications may need to draw short peak currents from the power supply. If the PSU overload protection type is hiccup or constant current limiting mode, then it will not be able to provide the current peak needed by the load. Some of our power supplies come with a peak power capability that makes them suitable for these kinds of applications. (e.g. HRP-150N series)

For open-frame power supplies with peak capability, the user should refer to the derating curves, and check the thermal requirements (a fan may be required).

Categories: Industrial, Medical, Operation

In general, there are two circumstances that will cause the power supply to shut down. The first one is the activation of the overload protection (OLP). To deal with this situation, we suggest increasing the rating of the output power or modifying the OLP point. The second one is the activation of over temperature protection (OTP) when the internal temperature reaches the pre-set value. All these conditions will let the Power Supply enter protection mode and shut down. After these conditions are removed, the Power Supply will be back to normal.

Categories: Industrial, Medical, Operation

When current drawn exceeds the rating of the PSU, the protection circuit will be triggered to protect the unit against overload/overcurrent. 

Protections of overload/overcurrent can be divided into several forms:

(1)FOLDBACK CURRENT LIMITING

Output current decreases about 20% of rated current, shown as curve (a) in the figure below. 

(2)CONSTANT CURRENT LIMITING

Output current remains at a constant level and within the specified range while the output voltage drops to a lower level, shown as curve (b) in the figure below. 

(3)OVER POWER LIMITING

Output power remains constant. As output load increases, output voltage decreases in proportion, shown as curve (c) in the figure below.  

(4)HICCUP CURRENT LIMITING

Output voltage and current keep pulsing ON and OFF repeatedly when protection is activated. The unit automatically recovers when the faulty condition is removed.

(5)SHUT OFF

 Output voltage and current are cut off when output load reaches protection range. 

NOTE: Protection mode of some of the products combines with different types of the forms mentioned, such as constant current limiting + shut down.

Recover method:

(1)Auto Recovery: PSU recovers automatically after faulty condition is removed.

(2)Re-power on: PSU restarts by manual AC re-power on after faulty condition is removed.

Note: Please do not operate PSU in overcurrent or short-circuit condition for a long period of time to prevent a shorten lifespan or damaging the PSU.

Categories: Industrial, Medical, Operation