High-Voltage Circuit Design Guidelines and Materials


Reading time ( words)

The Hubble telescope, the Cassini-Huygens mission, and other exploratory spacecraft utilize high-voltage DC power supplies for everything from vidicon camera tubes and mass spectrometers to radar and laser technologies. NASA has experienced performance problems with the 1.5 kV supplies because—as a 2006 report stated—“designers did not take the high-voltage problems seriously in the initial design.” The report cited very narrow parts parameters, electrical insulation problems in dielectrics, ceramics, bad geometries, small spacing, the use of the wrong insulating materials, and thermal expansion as causes for the power supply failures.

Designing a circuit that includes high-voltages requires a different—and much more rigorous—approach than seen with other PCB designs. And the need for more attention increases for high-density designs. Along with that approach, design teams also must become familiar with terminology that covers insulation, board materials, clearance, creepage, and altitude. Designers also should have an overall knowledge of regulations that can impact the circuit.

High-Voltage Design Problem-Solving Begins With the PCB Layout

All of us know that proper trace spacing in a PCB design maintains signal integrity and helps with preventing the propagation of electromagnetic interference. In high-voltage PCB design, trace spacing becomes even more important. If we rightfully consider the board as a series of conductive elements, the possibility of differences in potential—creating high-voltage flashover with narrow trace spacing—becomes a certainty.

Along with the IPC-2221 Generic Standard on Printed Board Design that establishes the design principles for interconnections on PCBs, the International Electrotechnical Commission (IEC) and the Underwriters Laboratories (UL) also produced IEC/UL 60950-1, the “Safety of Information Technology Equipment” standard, that describes safety requirements for products and details minimum allowed PCB spacing requirements. As a combination, the standards also set guidelines for PCB layouts that include two important parameters called clearance and creepage.

Using the IEC 60950 definition, clearance equals the shortest distance between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured through air. A small clearance value between two conductors establishes the environment for a high-voltage flashover or arc. Clearance values vary according to the type of PCB material used for the circuit, the voltages, and operating environment conditions such as humidity and dust. Those environmental factors—and others—decrease the breakdown voltage of air and increase the opportunities for a high-voltage flashover and a short circuit.

We can address clearance issues through ECAD/MCAD design principles. Since the bounding surface described in the IEC definition is the outer surface of an electrical enclosure, we can use 3D design tools and design rules to establish the clearance between enclosures and components for rigid and rigid-flex circuits. We can also apply good PCB design principles by isolating high-voltage circuits from low-voltage circuits. Fabricators often recommend placing the high-voltage components on the top side of a multilayer board and the low voltage circuits on the bottom side of the PCB. Other methods involve placing the appropriate insulating materials between high-voltage nodes and over any exposed high-voltage leads.

To read this entire article, which appeared in the January 2022 issue of Design007 Magazine, click here.

Share




Suggested Items

I-Connect007 Editor’s Choice: Five Must-Reads for the Week

01/20/2023 | Andy Shaughnessy, Design007 Magazine
We’re in the middle of show season, and it certainly “shows.” Thank you very much. I’m here all week. Don’t forget to tip your wait staff. This week, we published a variety of articles, columns, and news items, and much of it centered on trade shows. Technical Editor Dan Feinberg brings us a report from CES 2023. IPC announced the winners of the Best Technical Paper awards for IPC APEX EXPO 2023. And we have an interview with Altium’s Rea Callender about the company’s educational efforts at APEX and around the globe.

Altium Focuses on Design Education

01/16/2023 | I-Connect007 Editorial Team
Altium keeps its eyes on the designers of the future. The company has been working with colleges and universities for years, providing free seats of Altium Designer for the next generation of PCB designers and design engineers. At IPC APEX EXPO 2023, Altium will be providing software for the finalists in the IPC Design Competition just as it did last year. They offer a variety of other educational programs as well, including Upverter classes and a design competition that aims to address environmental change. Here, Rea Callender, Altium’s VP of education, discusses its educational programs and plans for the week of the show.

The Battle of the Boards

01/12/2023 | Patrick Crawford, IPC
Last year, IPC held its first-ever design competition at IPC APEX EXPO in San Diego. PCB designers from around the world competed in a series of heats during the months before the show, culminating in a showdown on the show floor between the top three finalists. Rafal Przeslawski, now with AMD, took home the top prize last year. This year, the competition is back for its sophomore year. I asked Patrick Crawford, manager of design standards and related programs for IPC, to “layout” the details on the design contest, including lessons learned in 2022 and what’s new for the 2023 competition.



Copyright © 2023 I-Connect007 | IPC Publishing Group Inc. All rights reserved.