Power Electronics

Then and Now

As Power Electronics Technology celebrates its 30th year, we conclude our series reflecting on product developments that appeared on these pages in 1975 and examine the technological progress that has been made since then.

For the PDF version of this article, click here.

In this fourth and final article, we turn our attention to products chosen from the November/December 1975 edition of Solid-State Power Conversion, the predecessor to Power Electronics Technology. The optocouplers/isolators, microprocessor power supplies and modular power connectors discussed here have much in common with currently available components. At the same time, there are some dramatic differences in functionality, performance and packaging between the components that were available in the 1970s and those that are being produced now.

Then Miniature Opto-Couplers/Isolators

This series of miniature opto-couplers/isolators includes 10 new models in the “SOC” series. They are electronically and mechanically interchangeable with the Monsanto MCT-2 series, thus offering the OEM designer an alternative source for these important devices. The units are a simple and economical way to eliminate highly detrimental ground loops in digital communication and signal-transmission systems that utilize both low-power and high-power components, or that carry signals over long distances. The devices offer very high minimum isolation voltages (5 kV) and faster rise times than those of earlier models. They are packaged in a plastic dual-in-line case that measures only 0.30 × 0.35 × 0.125 inches. (From $2.50/unit; 30 days.)
Sensor Technology Inc., Chatsworth, Calif. Solid-State Power Conversion, November/December 1975, p. 29

Miniature Optocouplers/Isolators

“Thirty years ago, prices for optoelectronic couplers were 50 cents in volume; now they can go for as little as 4 cents.” That's how Thierry Hernoult, R&D director of optoelectronics at Fairchild Semiconductor (South Portland, Maine), describes the dramatic decline in pricing over the time span. Today, demand for these devices is quite high because so many of them are used in power adapters, in battery chargers, for every manner of cell phone, portable product and the like.

Within the optoelectronic coupler package itself, there have been several types of construction over the years. Early on, there was a coplanar arrangement in which the photoemitter and photoreceiver portions lay at the same elevation, and a reflective surface above them enabled the light from the photoemitter to reach the sense element. Later on, an under/over configuration evolved in which the light output from the emitter was aligned directly with the optical input axis of the photoreceiver part.

A major application accounting for some 85% to 95% of today's usage is in power supply applications in which the optoelectronic isolator is connected in a feedback loop that drives a switch such as an FET on the secondary side of the transformer.

It is because optoelectronic couplers usually have to stand off a high voltage that they still tend to be relatively large, depending primarily on the distances between inputs and outputs, as well as the characteristics of the plastic housing in which they reside to achieve isolation. But some applications have evolved over the last 30 years that do not require this high isolation, so that in such cases the packages have tended to shrink to a surface-mount package such as the SO-8 or the Miniflat package (MFP). The latter has the same footprint as an SO-8, but a lower height.

Fairchild recently introduced its Microcoupler, which may be the smallest optoelectronic isolator on the market today. It is half the height of the Miniflat and its circuit-board footprint is approximately 2 mm × 2 mm. As for the operating environment, it was typically 85°C to 100°C, years ago. Holding the temperature to a particular maximum is essential, otherwise the light output from the photoemitter will fall off. However, Fairchild's Microcoupler can operate satisfactorily at temperatures of 125°C. Bandwidth of the early optoelectronic couplers was in the neighborhood of 1 Mbps. Today, 25 Mbps to 50 Mbps and even 100 Mbps have become possible.

Then 30-W Microprocessor Power Supplies

Microprocessor systems have special power requirements. The selection and control of voltage levels is important, as is the quality and shape of the input waveform to assure accurate and reliable operation of any microprocessor system. The new Series 4500/4600 Microprocessor Power Supplies are specifically designed to solve this problem by delivering power which is virtually free of noise (Total noise + ripple is 100 µV RMS max.) They have output voltage temperature drift of less than 100 ppm/°C, with waveforms specifically shaped for today's microprocessors. The Series 4500/4600 includes triple-, dual- and single-output models that provide extremely clean turn-on and turn-off, current limited waveforms with no overshoot. Available in AC input-voltage ranges of 105 V to 125 V at 50 Hz to 420 Hz, this family features input isolation of 50 megohms at 60 Hz, up to 500 V, across the entire operating temperature range of -25°C to +85°C. No derating is required for these high reliability units. Standard models for international AC line voltages, as well as brownout versions, are available.
— Dynamics Measurements Corp., Winchester, Mass.
Solid-State Power Conversion, November/December 1975, p. 33

Microprocessor Power Supplies

Thirty years ago, power supplies were analog, but since then, the shift to switching power supply technology has enabled greater efficiencies, to 85% and above; so a lot more supply can be packed into a far smaller enclosure. Today, a typical power supply might deliver 500 W, and it might measure 5.9 in. × 5.5 in. × 3.4 in. Thirty years ago, a 500-W supply would pretty much fill up your desk. However, regulation for modern supplies is still typically ±5% over line and load, with some at ±3%. Today, so much regarding microprocessor power supplies is governed by the Intel-driven specifications that are found at www.formfactors.org.

Thirty years ago the processor was driven directly from the main power supply at either 12 V or 5 V. The current was low enough that line and load regulation, as well as response time were not significantly impacted by the wiring interconnection. In today's processor power supplies it is necessary to provide a voltage regulation module (VRM) in close proximity to the processor to eliminate the inductance and associated voltage transients and delays that would exceed the operating limit of the processor that has now dropped to approximately 1 V. These VRMs are capable of providing nonisolated power at densities up to 100 W/cu in.

Thirty years ago, protection probably began and ended with a 3AG glass-cartridge fuse. Now, supplies can be equipped with overcurrent/undercurrent, undervoltage/overvoltage sensors, as well as short-circuit protection. An example of a supply today is the TPII 550-W ATX v2.0 PSU from Antec (Fremont, Calif.). It enables the user — via a control panel — to tweak the voltages of the 3-V, 5-V and 12-V main rails independently and also adjust the point at which the 12-cm fan switches on, in response to a rising demand for power. Today, there is a lot of demand for tweaking the voltage, especially in high-performance, gaming applications. In their quest for higher performance, the “overclockers” will raise the clock speed, thereby increasing the power consumption.

This power supply is SLI ready, which means it can accommodate a technology developed by NVIDIA (Santa Clara, Calif.), a graphics card maker, whereby a user can plug in two graphic cards into a chassis so that the graphics load is shared by both cards, thereby enhancing the graphics performance. NVIDIA established www.slizone.com to support its SLI initiatives. The street price for the Antec TPII is $134.95.

Then Modular Power Connector

Available in either 30 or 75 ampere sizes for wires from AWG No. 16 to No. 6, the AMP Power Lock Connector has a modular, hermaphroditic design. Rated at 600 Vac, the thermoplastic modules interlock to provide keyed and polarized connectors with a variable number of contact positions. Their hermaphroditic crimp/snap-in contacts are available loose, or on reels with a choice of silver-plated or tin-plated copper. They are suitable for free-hanging, surface mounting, or mate with similar connectors now in use.
— AMP Inc., Harrisburg, Pa. Solid-State Power Conversion, November/December 1975, p. 28

Modular Power Connector

The Powerlock connector series, introduced by ITT Cannon (Santa Ana, Calif.) a little over a decade ago, may or may not have a kinship with the AMP Power Lock connector of 30 years ago, depending on how you look at it. But according to Wilfred de Jong Vogelenzang, product manager of the ITT Powerlock product line at ITT Cannon, the company devised its series in response to a requirement in the entertainment industry in the early 1990s for safe, single-pole power connectors.

First, ITT Cannon enclosed the mating contact pair in a glass-filled plastic that safeguarded the handler. Then in 1997-1998, the company introduced a second-generation Powerlock series in which it changed the plastic compound with its glass component to Valox, an engineering plastic that is less prone to damage. ITT Cannon developed a keying system with notches located in various clock positions so that the wrong connectors cannot be mated inadvertently. This keying technique makes sure that neutrals are not connected to grounds, phase A lines to phase C lines, etc. The ITT Cannon Powerlock connectors are rated at up to 660 A and can handle up to 1000 Vac.

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