Medical Isolation Toroidal Transformer Design Considerations

Design Considerations

  • Low leakage current
  • Ground screens as needed
  • Thermal protection (fuses or switches)
  • 8 VA to 30 kVA
  • International medical safety approvals
  • Certificates of compliance
  • Low radiated and acoustic noise

Overview

Toroids are naturally well suited and widely utilized in variety medical power applications, for both patient and non-patient connected devices. Low stray fields allow for interference-free mounting, when installed in close proximity to CRTs or other sensitive components. Low impedance windings permit maximum surge power can be delivered in low duty cycle applications as – X-ray machines. Leakage current is a function of design, and precise repeatable manufacturing processes can certify every toroid meets the most stringent medical requirements.

Specifying Toroidal Medical Isolation Transformers

intltoroidThe design parameters of medical transformers are greatly impacted by rigorous constructional spacings, creepage distances, leakage current maximums, plus more safety agency mandated criteria – all of which serve to increase the transformers complexity, cost, physical size – and all of which degrade electrical performance.

As an example, as spacings between adjacent windings may need to be increased as a means to achieve a difficult leakage current spec.

However, increased spacings require more materials, which add to cost and size cost, but also will become apparent by negatively affecting electrical performance on such items as increased stray magnetic fields, worsening of regulation, increased temperature rise, and more. Thus, it is vital medical specs be extremely accurate, and conservatism through over-specification as it will add cost and degrade performance.

Leakage Current

Can be specified as a maximum guaranteed specification. Plitron’s automated test equipment can certify 100% of production is in compliance. Depending on circuit configuration, sometimes only a single winding requires a leakage spec – and not the entire transformer secondary side. Advise our engineers at the time of design, which leads, need low leakage.

In Rush Considerations

The complexity of medical approvals can be simplified through a reduction in the number of components on the transformer’s primary side. Plitron’s Imin technology provides a ‘transformer-based’ inrush solution eliminating the need for any external primary components. Unlike inrush thermistors, which operate at excessive temperatures and may require a reset time; or relays and actuators, which can arc and fail under adverse line conditions, Plitron’s Imin technology offers an absolute proven inrush solution that is highly compatible to medical installations.

Certification to Medical Standards

Certification to medical approvals can be a complex, lengthy, and expensive process. Often products have to be submitted more than once. Plitron can self certify transformers to medical ‘601’ standards for materials and construction – even at the prototype stage – which will expedite your entire produce approval process. As required, we can supply blanket certificates of construction to the safety agencies, thus alleviating their requirement to dissect, document and approve the transformer as a separate entity. Agencies can focus on product testing, and not have to verify transformer construction.

Stray Magnetic Fields

LowmagfieldThe nature of stray magnetic fields has little or no consistency; varies with product, line, load and even between transformers; and there is no uniform system nor standard to classify, specify, and measure fields. Paradoxically, medical applications demand low stray fields, while the construction required to meet medical specs tends to increase stray fields.

Plitron’s approach is to design for low stray fields at the onset. Although seemingly redundant an rhetorical, attention to field containment as a function of design will always provide the best long term solution, with the lowest amount of variability in the field, and the least amount of external ‘band-aid’ magnetic shielding required.

Plitron engineers have many advance ‘invisible’ design tools at their disposal, such as materials selections, winding configurations, various construction which can lower stray fields by measurable amounts at the time of design. In addition, we can derive custom testing for your product to ensure total compliance.