Whether a medical device can function at its maximum effectiveness in a hospital depends not only directly on the machine's technical performance but also crucially on the quality of its power supply. The quality of the power supply directly impacts the operational stability and reliability of the medical equipment, and can even lead to major medical equipment accidents and significant economic losses.
Currently, most medical equipment in China is powered by 220V AC mains power. Due to the diverse power requirements of different types of medical equipment, centralized power supply structures are the most commonly used. This involves a centralized power converter generating the required output voltage levels. Because of its low cost, high efficiency, adjustable output voltage, low output noise, and fast dynamic response, it is very suitable for medical equipment and is currently the most widely used power supply method for medical devices.
Because medical electronics production volumes are generally relatively low, designers must consider either purchasing or manufacturing them themselves. Designers of medical electronics rarely consider designing their own offline power supplies. This is because the investment required for such specialized design and testing is disproportionate to the final production scale, and equipment manufacturers find it difficult or impossible to amortize the investment invested in the design phase with the production volume. Therefore, it is more cost-effective to purchase power supplies directly from companies that already possess the relevant specialized design capabilities and testing technologies.
Safety and isolation are key differences between commercial and medical power supplies. Typically, aside from some laboratory analytical instruments, medical equipment is installed near hospital beds or operating tables, close to people and operators, and its casing is frequently touched. Medical equipment contains various high- and low-voltage components; if the isolation between these components or the insulation of the casing material is inadequate, it can be extremely dangerous.
When selecting or building a good power supply system for medical equipment, it is essential to pay attention to improving the power supply's electromagnetic compatibility and immunity to electromagnetic interference. The following aspects should be considered:
Design. PCB design and layout are crucial. Power supplies typically contain high-frequency signals, and any printed circuit board (PCB) trace can act as an antenna. The length and width of these traces affect their impedance and inductance, thus influencing frequency response. Even traces transmitting DC signals can couple to RF signals from adjacent traces, causing circuit problems. Therefore, medical power supplies must be sourced from reputable brands and companies with strong R&D capabilities. These products guarantee superior quality in design and manufacturing technology.
Shielding. To suppress radiation generated by the switching power supply and eliminate the impact of electromagnetic interference on other electronic devices in the medical equipment, the best approach is to shield the power supply's magnetic field and then attach the entire shielding cover to the medical equipment's housing or the ground. This is a method that achieves twice the results with half the effort.
Certification. At this stage, power supplies for general medical devices generally need to pass electromagnetic compatibility and electromagnetic interference (EMI) tests such as FCC-B, CISPR22-B, EN55011, 55022, 61204, and 61000. Choosing products that have completed these tests not only ensures that they will not have electromagnetic influences on other electronic components in the device, but also reduces the development cycle of medical devices and the inspection time before they are released to the market.
Size and high power density. Currently, in addition to the development of multifunctionality, high detection and regulation accuracy, medical devices are also trending towards smaller size and portability. This requires that the power supply of medical devices must have high power output while maintaining a small board area.
Special applications. Currently, most centralized power supply products on the market have standard outputs. Even if some power supply products allow output adjustment via external circuitry, the adjustment range is limited, and stability issues exist. What if low voltage, high current, or extremely high DC voltage are encountered? Custom solutions can be used, but these are very expensive, regardless of customer acceptance.
During the research and design process, there will inevitably be various problems. This requires our researchers to continuously summarize their experiences during the design process in order to promote the continuous innovation of products.
