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Bi-directional converter shrinks battery array to one cell

Case study: Portable X-ray system

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Source for 28V needed to be lighter, reliable and portable

Source for 28V needed to be lighter, reliable and portable

New solid-state X-ray technology allows medical X-ray scanners to be more portable and battery operated, enabling medical professionals to check patients in any location. Medical X-rays typically need a short pulse of high-intensity radiation energy, which can conveniently be stored and supplied to the X-ray diode by a supercapacitor, in this case charged to 28V. Normally the 28V would be sourced from a number of Li-ion batteries in series. However, in a portable application, this type of battery array and charging system is too large and too heavy. The key goals were:

  • Find an alternative to heavy and bulky multiple-cell battery solutions
  • Fast charging of the supercapacitor requires a high current pulse
  • Long battery life to minimize the need for recharging

Bi-directional converter allowed for just one battery array

Bi-directional converter allowed for just one battery array

Use of a bi-directional DC-DC converter reduced the battery array to just one 2.7V Li-ion cell, reducing size and weight significantly compared to a typical boost converter solution. In addition, the bi-directional converter delivered higher efficiencies when charging the supercapacitor from a low voltage source, extending battery life. Key benefits were:

  • Ultra-small, lightweight solution (8.6cm2 footprint, 16g weight) compared to a boost converter solution
  • Unique bi-directional converters (DC-DC transformer) available as standard products
  • Higher efficiency achieved using low-loss Sine Amplitude Conversion topology

Bi-directional VTM, operating in reverse mode, enabled highly-efficient x12 transformation

A Vicor VTM, operating in reverse, stepped-up the 2.7V input to provide a nominal 32V rail with an efficiency of more than 94%. For the supercapacitor charging circuit, a ZVS Buck-Boost converter regulated the 32V and provided the necessary current limiting. This architecture was accomplished in a footprint of just 8.6cm2. To analyze this power chain, go to Vicor Whiteboard online tool.

Learn more about the modular approach power.

The power delivery network

Portable Xray
VTM current multiplier

VTM current multipliers

Input: 0 – 60V

Output: 0 – 55V

Current: Up to 115A

Peak efficiency: Up to 97%

As small as 22.83 x 8.52 x 4.9mm

ZVS buck-boost regulators

ZVS buck-boost regulators

Input: 8 – 60V

Output: 10 – 54V

Power: Up to 150W continuous

Efficiency: Over 98%

10.5 x 14.5 x 3.05mm


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