Medical Electronics
Choosing and applying the optimum DC/DC converter for medical applications
By Rolf Horn, applications engineer at DigiKey D
esigning a power supply that runs off AC mains or battery power is complicated. The designer must develop a solution that provides a stable voltage
and current across varying loads while operating efficiently to minimise power dissipation. However, when the power supply is intended for a medical product, the design becomes more complicated due to electromagnetic compatibility (EMC), strict safety requirements regarding electrical contact with a patient, and protection from electromagnetic interference (EMI). Meeting these requirements is costly and time-consuming for designers developing medical power supplies from the ground up. Commercial modular DC/DC converters are an alternative, but care must be taken when selecting and applying these solutions. This article briefly describes the role of a DC/DC converter in a power supply circuit and outlines the selection criteria and special considerations demanded for medical applications. It then introduces example devices from XP Power and shows an application model.
The role of a DC/DC converter While batteries are rated with a nominal voltage, the output is affected by factors such as state of charge, peak demand, and temperature. A key characteristic is that voltage output declines as the battery discharges. Yet, ICs and other sensitive components require a steady voltage to function correctly. A DC/DC converter offers a solution by regulating the input voltage to provide a reliable and consistent voltage output (or outputs) to power the end product. DC/DC converters are common in mains- powered products, too. An initial AC/DC converter regulates the AC mains to a DC voltage with one or more DC/DC converters. Then, further regulation brings that voltage to a suitable level for the end-product.
20 May 2025
Figure 1: Modular devices such as the JMR series integrate the primary elements of a DC/DC switching regulator into a single device that is compact, reliable, and easy to design in. (Image source: XP Power)
Topologies for DC/DC converters can be linear or switching. Linear regulators are simple and robust devices, but their efficiency declines as the difference between input and output voltage increases. Also, linear regulators can only step down (buck) rather than step up (boost) or invert a voltage. Not being able to boost voltages leaves untapped potential in batteries.
Switching regulators use a switching element that is pulse width modulated (PWM) and typically comprises one or two MOSFETs paired with one or two inductors and capacitors for energy storage and filtering. The main reasons designers choose switching regulators are high efficiency and high power density. Moreover, the regulators can boost, buck, and invert voltages.
The challenges for designers using switching regulators include design complexity, cost, and potential EMI issues due to the switching elements. It is possible to design a DC/DC switching regulator from scratch, and such an approach can save some cost and space, but it is complex and time- consuming. An alternative is to select from the wide range of commercial modules, such as XP Power’s JMR series, that integrate the primary elements of the switching regulator into a single device that is compact, reliable, and easy to design into a product (Figure 1).
Selecting a DC/DC converter There are many factors to consider when choosing a DC/DC converter. Some are obvious; for example, the application will determine input and output voltages and
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input and output current. Others are more nuanced. For example, maximizing efficiency requires
consideration of the typical load profile of the end product. Also, the designer should examine the datasheet efficiency curves for the shortlisted DC/DC converters to ensure the end product generally operates at the converter’s efficiency sweet spot.
XP Power’s JMR1024S05 is a good example of a DC/DC converter for a medical application. This converter is an ultra-compact, printed circuit board (pc board) mount medical device measuring 20.3 x 31.8 x 10.2 millimetres (mm), with 3 mm through-hole leads. It has an output of 5 V from a nominal input of 24 V (min 9 V, max 36 V). The module features a maximum output current of 2 amperes (A) and a full-load input current of 491 milliamperes (mA). The output ripple voltage is 75 millivolts (mV) peak to peak (pk-pk), and its efficiency is 84.9 per cent.
The module features a low no-load power consumption of 6 mA, which boosts efficiency and lowers power dissipation. A further no-load power consumption savings of 3 mA can be made by remotely inhibiting the
module (Figure 2). The module is on if Pin 1 is an open circuit; the module is off if Pin 1 is connected to a current source of 2 mA to 4 mA, or if 2.2 V to 12 V are applied to Pin 1 relative to Pin 2.
XP Power offers alternatives in their 10 watt line. The JMR1048S12, for example, operates from a nominal 48 V input (18 V to 75 V) and delivers a 12 V output with a maximum output current of 833 mA. The full-load input current is 237 mA, and when operating in this condition, efficiency is 88 per cent.
The JMR1012D15 operates from a nominal 12 V input (4.5 V to 18 V) and delivers a ±15 V output with a maximum current of 333 mA. The full-load input current is 957 mA, and when operating in this condition, efficiency is 87 per cent.
The switching frequency for the JMR 10 watt series is 300 kilohertz (kHz).
Special requirements for medical applications
Medical products demand more from a DC/DC converter because electrical components used in the end products are subject to the strict IEC 60601-1 medical safety standard. According to IEC 60601-1, the “applied part” is defined as the element of the medical device that comes into direct contact with a patient, or has parts that are likely to come into contact with the patient during the
Figure 2: The no-load power consumption of the JMR1024S05 can be reduced to 3 mA by remotely inhibiting the module. (Image source: XP Power)
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