Coreless design enables converter operation in intense magnetic fields

January 26, 2017 // By Graham Prophet
Powerbox (Gnesta, Sweden) has designed a coreless technology platform to power medical and industrial equipment operating in very high magnetic field environments such as magnetic resonance imaging or particle accelerators.

Using high-frequency switching topologies and digital control with proprietary firmware to optimize efficiency and voltage regulation, the GB350 buck-converter module is the first building block in its category that is able to operate safely when exposed to high magnetic fields of 2 to 4 Tesla. GB350 delivers an output power of 350W and when higher power levels are required it can be paralleled using an interleaving, thus reducing EMI.


Medical and industrial applications such as magnetic resonance imaging (MRI) and particle accelerators (PA) generate high magnetic fields to induce the RF energy required to activate the hydrogen nuclei in the case of imaging, or to accelerate particles in research and industrial equipment. Modern MRI systems usually generate 1.5 to 4 Tesla, making conventional power supplies using ferrite material useless due to inductance saturation as a result of the MRI magnet disturbing the energy transfer. To prevent parasitic saturation, power supplies are traditionally positioned outside the shielded operation room. Installing the power supplies remotely requires long cables with subsequent power losses, and it is also a big challenge to power the latest generation of measuring equipment that require stable and tightly regulated voltages under fast transient load conditions.


To reduce energy consumption and to guarantee the level of quality required by integrated equipment, systems manufacturers are now integrating local power supplies near to the load. However, placing equipment directly in the radiated magnetic field requires ‘coreless power units’ and an advance switching power stage.


Powerbox’s GB350 coreless power unit is fully controlled by a digital processor that manages the complete power unit from switching parameters (e.g. dead-time and duty-cycle optimization) to output voltage characterization. For flexibility and to allow the possibility to re-profile the power unit characteristics when equipment manufacturers upgrade new hardware or implement a software revision, the GB350’s MCU can be reprogrammed with a download.


The standard GB350 platform delivers a nominal current of 50A