3D power packaged DC/DC converters for medical applications

“DC/DC converters with medical-grade isolation can be used in combination with AC/DC power supplies or battery-powered equipment, which not only reduces the cost of end products in medical applications, but also meets the highest level of safety standards.

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DC/DC converters with medical-grade isolation can be used in combination with AC/DC power supplies or battery-powered equipment, which not only reduces the cost of end products in medical applications, but also meets the highest level of safety standards.

Electronic equipment is increasingly being used in different medical and home diagnosis and treatment environments. The equipment used must strictly comply with relevant electrical safety standards: IEC 60601-1:2005 and its accompanying documents and national standards, including European EN 60601- 1:2006.

When considering the AC/DC power supply required by the product, refer to the application guide of the latest version of the safety standard, which mentions the “protective measures” (MOPs) that the operator and patient environment should have. It seems to be more sensible to directly specify the power supply with the highest safety level, that is, with dual patient protection measures (MOPPs). The maximum rated power supply voltage and leakage current meet the requirements of the CF type (heart floating) that contacts the patient; the CF type Refers to the connection of electricity to the organ for monitoring or stimulation. Battery-powered equipment may be deemed to be inapplicable to safety standards. However, in some cases, it is not enough to rely on fully certified AC/DC, and in other cases it is above the specifications. There are also some applications that are battery-powered. The equipment requires internal safety isolation.

Taking AC power supply equipment as an example, there must be at least 2 x MOOP or MOPP isolation from the AC line to the output, depending on whether the equipment will be used in the environment of the operator or patient, respectively. However, the output of the patient connection must be isolated from the ground by at least 1 x MOPP to prevent the patient from becoming a “fire wire” to other malfunctioning equipment, allowing lethal current to flow through the patient to the ground. In this case, an additional isolated DC/DC converter can power the circuit connected to the patient. If it has suitable medical grade isolation, it can use an AC/DC converter with only 1 x MOPP output isolation.

In another case where the signal connection is not specified, such as the communication port of AC or battery-powered equipment, there must be 2 x MOPP between the patient connection and the signal to prevent external faults from turning on the signal. Likewise, additional DC/DC converters can provide the required isolation. Figure 1 gives an example of a special case. A Class I, 2 x MOOP AC/DC power supply with unspecified signal input, plus a 2 x MOPP DC/DC converter, can provide the necessary isolation for the signal input. Allows the use of lower-cost “operator-level” AC/DC power supplies in patient-connected environments.

The DC/DC converter usually only needs to provide low power for the patient connection interface, so it is relatively small and low in cost. Due to its size, its coupling capacitance is usually very low, and the leakage current is therefore very low. Compared with the case of using AC/DC alone, it can provide a higher level of patient connection.

Figure 1: The highest level of medical power solutions connected to patients can be realized by using affordable devices

Care must be taken to choose DC/DC converters for medical applications

DC/DC converters have become commercial devices, and converters with various isolation levels, with or without agency certification, can be purchased from many sources. The designer should know that the high withstand voltage level usually only represents transient immunity. If it is not certified by the relevant standards of a special agency, the product may not be suitable for use as any type of safety barrier. For medical applications, the DC/DC specification should indicate the level of protection measures, MOOP or MOPP of the specified system voltage (usually 250VAC). DC/DC may legally obtain 2 x MOPP certification, but it is only possible at 30VAC. It is very dangerous if the system voltage is “normal” AC power. Medical-grade DC/DC converters are not common because it is not easy to achieve a high isolation level inside the device. The standard requires the use of solid solid insulating materials or a large distance between input and output. For example, the certification of 2 x MOPP/250VAC requires a creepage distance of 8mm, which is a big difficulty for the internal structure design.

The R05CT05S recently released by RECOM is an example of a DC/DC converter that achieves high-level medical isolation (Figure 2). This is an economical 0.5W device with a nominal input of 5V and an output of 3.3V, 5V, 3.7V, or 5.4V, which powers the low dropout regulator (LDO). The converter uses a compact 10.3mm x 7.7mm SMD package with a height of only 2.65mm, suitable for space-constrained applications. The highlight specification for the medical application of this product is 2 x MOPP/250VAC continuous rated voltage, and the test voltage is 5kVAC, which meets the IEC/EN 60601-1 standard. It also has a coupling capacitance of 3.5pF, and the leakage current for 250VAC/50Hz applications is negligible. Its rated voltage in non-medical applications is even better. C 800VAC reinforced isolation working voltage complies with EN 62368-1 standard. The maximum operating temperature can reach 140°C during derating. The device functions include enable, synchronization, adjustment and undervoltage lockout.

Figure 2: 2 x MOPP/250VAC rated voltage isolated DC/DC converter

Advanced power packaging for medical-grade isolation

The designer of R05CT05S must take a new approach to product packaging to have both functionality and high isolation level. The traditional toroidal transformer cannot meet the insulation requirements and the bobbin E core or similar is too large, so the switching frequency is pushed up to 8MHz, allowing fewer winding turns and smaller planar transformer cores, while using a sturdy core Insulation between windings meets medical grade requirements. Even at high switching frequencies, the advanced circuit design of the embedded die can maintain good efficiency. After the chip is wire bonded to the DVE SOIC-16 lead frame, the entire product is overmolded.

in conclusion

Medical-grade certified high-isolation DC/DC converters are valuable devices that can achieve the required isolation levels for the most sensitive applications, including CF-type patient connections. Through careful application, the use of RECOM R05CT05S when designing a system can reduce costs to the greatest extent without compromising safety. The advanced circuit and 3D power packaging technology used in this product is an essential technology for RECOM's latest products, and continues to push the company toward smaller, more efficient, and more cost-effective DC/DC and AC/DC converters in a wide range of applications such as medical care. The goal is to move forward.

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