Articles and Publications by Joe Randolph
This article was published in the October 2018 issue of InCompliance Magazine. For safety approvals of information technology equipment (ITE), standards in the USA and most countries worldwide that used to be based on IEC 60950-1 are transitioning to a new base standard, IEC 62368-1. The corresponding standard in the USA is UL 62368-1, and in Europe, it is EN 62368-1. For ITE products that connect to ordinary AC mains power of 120/240 Vrms, the new IEC 62368-1 standard has added new requirements for the metal oxide varistors (MOVs) that are typically used for surge protection. The new requirements are intended to further reduce the likelihood of fire or electric shock that might result from the failure of a MOV. The wording of the new MOV requirements has caused some confusion among design engineers. This article is an attempt to explain how the new requirements will affect the design of a typical AC mains power supply.
This article appeared in the January 2017 issue of InCompliance Magazine. While it may seem surprising that lightning is a threat to comparatively short cables that are typically routed indoors, field experience has shown that lightning damage to Ethernet ports does, in fact, occur. This is especially true in residential installations with multiple grounds, point-of-load surge protectors, and a lot of interconnected equipment. The article is targeted at product managers and design engineers who seek to improve the lightning immunity of Ethernet ports on their products. The desire to achieve improved lightning immunity can be based simply on reducing field failures or possibly the need to comply with new Ethernet surge requirements in Telcordia GR-1089, ITU K.20, ITU K.21, and ITU K.45. The introductory portion describes the basic lightning coupling mechanisms that can affect Ethernet cables, while the remainder of the article is primarily a tutorial and how-to guide for implementing robust, low-cost surge protection for Ethernet ports.
This paper was presented at the 2014 IEEE Symposium on Product Compliance Engineering, where it received the Best Paper award. The paper discusses lightning damage to Ethernet and POTS ports connected to cables routed entirely within the same building. Manufacturers in both the USA and Japan have reported surprisingly high rates of lightning damage to ports on optical network terminals used for fiber-to-the-home delivery of telecom services. Similar damage has been reported on VOIP PBXs. While there are three known mechanisms by which lightning can make a couple onto inside wiring, their occurrence is believed to be statistically infrequent. The paper discusses these three known mechanisms as well as three new theories that are currently under study. All three of the new theories are based on the notion that surges on the AC mains are being coupled onto inside wiring communication cables. While research on these new theories continues, some guidelines are provided for manufacturers who wish to implement enhanced surge protection on Ethernet and POTS ports connected to inside wiring.
This paper was presented at the 2012 Symposium of the IEEE Product Safety Engineering Society, where it received the Best Paper award. The paper provides an introduction to the types of lightning surges and AC power fault surges that commonly affect the signaling cables of telecom network infrastructure and terminal equipment. Discussion is limited to twisted-pair copper lines such as telephone tip/ring cables and Ethernet cables. Surge types addressed include induced surges caused by nearby lightning strikes, induced AC voltages caused by fault conditions in adjacent AC power cables, and events caused by direct contact with AC power mains. Some general guidelines are provided for evaluating the surge tolerance of a given design based on an analysis of the applied surge and the available paths for surge currents to flow. This type of analysis will often identify potential weaknesses based strictly on a review of the proposed design prior to performing any actual surge tests.
Joe summarizes his perspective on the circumstances where it is appropriate to bring in an outside technical consultant. He describes various situations where it is cost-effective to hire a technical consultant and describes the attributes you should look for in a technical consultant.
The basic functions of a DAA (Data Access Arrangement) or FXO (Foreign Exchange Office) phone line interface circuit are essentially identical, but the specific performance requirements that must be met will differ depending on the application. This application note describes ten key questions to answer before you commit to a particular implementation strategy.
The basic functions of a SLIC (Subscriber Loop Interface Circuit) or FXS (Foreign Exchange Subscriber) phone line interface are essentially identical, but the specific performance requirements that must be met will differ depending on the application. This application note describes seven key questions to answer before you commit to a particular implementation.
This is a reprint of an application note that was originally published as Midcom TN #98. It describes a very basic, rugged, and inexpensive transformer-based phone line interface circuit. Included are a schematic diagram, parts list, and cost estimate.
This is an expanded version of AN-4. A second circuit has been added that provides some enhancements that may be desirable for certain applications. Also included is a brief review of how transformer-based DAA and FXO circuits compare to silicon DAA and FXO circuits.
This application note provides a brief review of how lightning surges appear on phone lines and explains the terminology that is typically used in discussing lightning protection of phone line interfaces. With this background, several common mistakes in the design of phone line lightning protection circuits are described.