Whiteboard of the Week: Radiological Imaging Flat Panel Display

February 2, 2015
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Johnny Yuen, one of our senior applications engineers, developed a solution for a flat panel display, which was recently featured as one of our Whiteboard Power Chains of the Week. We talked with Johnny to find out how the requirement for an ultra-low profile was met using Vicor ZVS Buck Regulators.

Why did your customer require such a low-profile solution?

Flat panel display power chain - whiteboardThe project was for an ultra-thin flat panel digital detector used as a display for a wide range of radiological imaging, including medical, surgical, scientific and industrial applications. The customer wanted to make the panel as thin as possible, and had encountered problems creating a power system that had a sufficiently low profile.

This product looks like a tablet computer: it’s only 7 mm thick, full-color, and is able to record and display the image results in real time. Its main use is in medical applications, where it is used for X-Ray, CT Scans and Radiological Scans.

The radiologist will save the images produced onto the device, allowing the patient to bring all the images to their consultation with a specialist. Clearly the thinner the product, the more easily it can be carried around.

Was the thickness of the display the only concern?

The thickness was important, but the customer was also very keen to minimize the weight: as some patients would be weak, it was important to develop a product that even very sick people would be able to carry.

The display also needed to be specially coated to prevent the growth of bacteria, although this didn’t impact the design of the power chain.

How important was power efficiency?

Efficiency was important, although the primary reason was not to conserve energy. As the power consumed is dissipated as heat, this product needed to maximize efficiency to ensure that the product didn’t get uncomfortably – or dangerously – hot.

Why did you choose Buck Regulators for this design?

The ZVS Buck Regulator is one of the lowest-profile converters available, only 2.6mm above the board, which enabled the customer to meet the physical design goals of the project.

Their high efficiency was a key factor in reducing the heat generated by the device, and the low demands on the passive components also helped simplify the design.

Did the use of power components provide any particular benefits?

The customer actually wanted to develop a family of products, offering different display widths to support larger images. Larger displays require more power, but this could easily be accommodated by replacing the Buck Regulator with another (higher output power) product in the family. The Buck Regulators were pin compatible, use inductors with the same footprint and the same output and input ceramic capacitors. This flexibility made it easy to support a range of products from the same PCB.

In fact by using these Vicor power components, we were also able to support any future requirement for different working voltages.

This reduced the time required to develop the power chain, and more importantly it allowed the customer to focus their engineering resources on developing more functionality and a wider range of products. It also ensured that the customer was able to get the family of products to the market quickly, giving them a lead over potential competitors.

Do the passive components have a significant impact on the design?

Yes! The customer was particularly pleased that the Vicor components do not require Tantalum Polymer Solid Capacitors (POSCAP) or standard Tantalum capacitors.

The combination of high switching frequency with the low ripple and soft switching inherent in the ZVS topology means that there are no stringent requirements for input and output capacitance for the Buck Regulators. This means that the power chain needs only low-cost ceramic capacitors, which are inherently more reliable than the capacitors required by other solutions.

Did you need any heatsinking for this application?

It was particularly important to avoid the bulk and weight of a heatsink, and like most applications, the efficient conversion and low thermal impedance package meant that our products did not need heatsinking.

The design used a multi-layer PCB to maximize cooling. The System-in-Package (SiP) uses a Land Grid Array (LGA) that has large pads, which provide a very low thermal impedance path, taking the power dissipation, as heat, through the LGA to the PCB.

 

You can view Johnny’s power chain design, modify and analyze it by clicking here

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