Medical power supplies must be safe, efficient and quiet.

In medical technology, the protection of patients and hospital staff has top priority. For this reason, medical power supplies are subject to strict requirements regarding safety, reliability and EMC. In this blog article you will find out how medical technology can benefit from the experience gained in machine building and system engineering.

Power supplies have to convert voltage as safely and efficiently as possible, while ensuring smooth operation over many years and in the tightest of spaces. Although this is a principle that applies to medical technology and to machine building alike, it is the industrial engineering segments where standard power supplies that meet these requirements are much more widespread. In turn, this means that medical equipment manufacturers are often dependent on customised rack or panel-mount power supplies.

Medical applications in hospital technology, building technology, laboratory technology and imaging diagnostics in particular stand to benefit from high industrial standards and rapid availability when it comes to power supplies. With its medical power supplies that have machine building in their DNA, PULS bridges the gap between the two fields of application.

Protection against electric shock 

In addition to basic safety, EN 60601-1 primarily focuses on the functional safety of medical equipment. In the case of power supplies, this means protecting patients and operators from electric shocks in everyday hospital life – both during normal operation and in the event of a fault.

The highest protection level is 2 MOPP (Means of Patient Protection), which is intended to ensure the safety of the patient as someone who may be in a weakened state. In the power supply, this is ensured by appropriately sized clearance and creepage distances, thicker insulation between the primary and secondary circuits, and compliance with the stipulated leakage currents.

We have modified our PULS CP series of industrial power supplies in a way that ensures they fulfil the medical specifications for 2 MOPP. This offers manufacturers the flexibility and safety to use the power supplies with the ending "-M1" nearby patients without a second thought.

Protection against electromagnetic interference

Medical equipment also has to produce high levels of electromagnetic immunity to external radiation, such as mobile radio signals, but at the same time it must not interfere with the technology in its vicinity. This means that it is subject to clear regulations for electromagnetic emissions. Electromagnetic compatibility, or EMC for short, is a collective representation of the interference immunity and emissions that an item of equipment demonstrates. The limit values for medical technology are specified in IEC 60601-1-2 (Edition 4).

These specifications repeatedly present manufacturers of medical power supplies with technical challenges. Due to high-frequency noise, output ripple and noise voltage, many switch-mode power supplies cause electromagnetic interference both on the lines and through radiation.

Our development engineers reduce interference within the circuit design itself as much as possible, allowing its industrial power supplies to achieve excellent EMC values. For our medical power supplies, we have once again gone one better, ensuring successful medical EMC testing according to IEC 60601-1-2 (e.g. EN 55011 Class B for radiated interference emissions).

Protection against device failures

Reliability and durability are often key considerations in the process of selecting system components in machine building and system engineering. Many machines are designed to continue operating for years or even decades – and the same is true of medical technology. In the medical field, however, reliability takes on another dimension: to maintain patients’ health and help them recover, reliable systems are crucial.

This is an aspect that we also bear in mind when developing our medical power supplies. The focus is on maximising the minimum service life and the MTBF (Mean Time Between Failures). We provide in-depth specifications for both values and publishes this information in the datasheets for each power supply.

The key to ensuring excellent reliability and a long service life is achieving an high efficiency. The higher the efficiency, the lower the power losses and, as a result, the less heat is generated inside the power supply. This is important because a 10°C temperature increase in the power supply halves the service life of electrolytic capacitors. Although losses of this kind do not necessarily entail an immediate failure of the power supply, they do compromise the service life of the power supply as a whole.

Calculation example: When it comes to efficiency, every percentage point counts

With our medical power supplies, we achieve efficiency rates of 94.3% to 95.2% depending on the performance class. A calculation example illustrates the importance of this rate: if efficiency is 95.2% (as it is in the case of the CP10.241-M1, 24V, 10A), losses amount to 4.8%. With 240W output power, the no-load losses between input and output are 12.1W, dissipated to the environment by way of heat (see diagram 1).

To understand the importance of every efficiency percentage point, it is essential to draw a comparison with a power supply whose efficiency amounts to just 91%: while this 4.2% difference might not sound significant, it results in almost double the no-load losses at 23.7 W.

In a test setup, PULS ran both units in identical boxes (with a volume of 3.15 l) and under identical conditions (load: 8 A / input voltage: 230 VAC) for four hours. After this time, the temperature difference was already 7.8°C. It is not just the power supply itself that is affected by this higher temperature: the surrounding system components also suffer.

Efficiency and power losses in medical power supplies Efficiency and power losses in medical power supplies
Graphic 1: Efficiency of the medical power supply CP10.241-M1.

Apart from the service life, the MTBF also worsens as a result of high temperatures. The MTBF describes how many failures can be expected as a statistical average when operating a certain number of units over a specific period of time.

A simple example illustrates this: if the MTBF value is 1,000,000 hours, for example, this means that statistically one unit will fail every 1000 hours if 1000 units are installed. Early failures are not included in this calculation because manufacturers exclude them as part of quality assurance. The effects of wear do not play a role in the calculation of the MTBF either, as no age-related failures occur during the use phase (see diagram 2).

We make sure that both our medical power supplies and our industrial power supplies have a high MTBF (for example, at 24V, 5A and 40°C, the CP5.241-M demonstrates an MTBF of 867,000 hours according to MTBF standard SN 29500). The units are therefore extremely reliable and have a very low failure rate.

MTBF - bathtub curve MTBF - bathtub curve
Figure 2: The phase of random failures (phase B) is decisive for the MTBF.

Protection against noise pollution

Highly efficient power supplies offer another advantage in that they allow for passive convection cooling, something that has become the standard for power supplies in machine building and system engineering. Given that less heat is generated in the power supply overall, it can be dissipated from the unit via a cooling air flow and the aluminium housing. This means that the units do not require fans to remove the warm air – a feature that works across the entire power range.

This aspect is particularly attractive in medical technology. Fans inevitably generate noise and this can be perceived as annoying, especially if the equipment is near the patient. As a mechanical component, fans are also more frequently affected by failures.

By contrast, power supplies with convection cooling operate silently in the background, promoting a healing environment for patients and enabling maintenance-free operation.

New opportunities for developers of healthcare technology

Medical power supplies from PULS Medical power supplies from PULS
Graphic 3: PULS offers medical power supplies for three different power classes 120W (24V, 5A), 240W (24V, 10A) and 480W (24V, 20A).

Given the high standards of hygiene that hospitals and laboratories have to meet, medical equipment designs avoid corners and edges wherever possible. This makes units easier to clean and disinfect – but at the same time, a rounded design substantially reduces the space available for electronics. Power supplies that are as compact as possible suit this scenario and are opening up new possibilities in medical design.

Thanks to the high efficiency levels of its power supplies, PULS is able to create designs that are highly compact and yet still comply with all the required protective measures for the patient environment. Most medical power supplies are larger than their industrial counterparts due to the additional insulation measures they require, such as larger clearance and creepage distances. For its medical power supplies, however, our PULS developers have succeeded in using housings that are identical to those used in standard power supplies for machine building and system engineering.

This makes it possible to accommodate 240W in a housing measuring only 39 x 124 x 117mm (width x height x depth). As a result, medical technology is also reaping the benefits that the progressive miniaturisation of system components is bringing in machine building.

Another industry feature that is gaining a foothold in an increasing number of sectors is the DIN rail. The most important arguments in favour of assembling system components on a DIN rail are quick installation and maximum flexibility, which enables a modular system structure. This means that individual components from different manufacturers can be combined to create a customised system that makes it possible to achieve the efficiency, performance and price levels required for the application. Another advantage of DIN rail assembly is that it allows users to mount power supplies from different performance classes on a single mounting system – something that also makes it easier to retrofit or replace components.

Summary

Manufacturers of medical devices tend to use open frame power supplies: most power supplies with medical approval available on the market are based on this design. With the M1 units in the CP series, PULS is taking a different approach. Based on our successful industrial power supplies, we are developing an expanding medical technology portfolio with solutions currently available for three different power classes: 120W (24V, 5A) , 240W (24V, 10A) and . Our developers are driven by a mission to combine the efficiency and reliability found in machine building and system engineering with the safety standards that the medical sector demands. The result is secure, durable and compact medical power supplies that benefit system developers, users and patients alike.

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