A revolution in the design of computer power supplies half a century ago

Half a century ago, improved transistors and switching voltage regulators revolutionized the design of computer power supplies. Apple, for example, gained advantages - although it was not she who launched this revolution, despite the statements of Steve Jobs.

Without Intel inside: X-ray shows the components of the switching power supply used in the original Apple II microcomputer, released in 1977

Computer power supplies are not given due attention.

As a technology enthusiast, you probably know which microprocessor your computer has and how much physical memory it has, but it is likely that you do not know anything about its power supply. Do not shy away - even manufacturers are developing PSUs last.

It’s a pity, since it took quite a lot of effort to create a PSU for personal computers, and this was a serious improvement compared to the circuits that fed other consumer electronics until the late 1970s. This breakthrough was made possible thanks to the huge leaps in semiconductor technology made half a century ago, in particular, improvements in switching voltage regulators and innovations in integrated circuits. But at the same time, this revolution passed public attention, and is even unknown to many people familiar with the history of microcomputers.
')
In the world of BP, there were some outstanding champions, including a person whose mention may surprise you: Steve Jobs . According to his authorized biographer, Walter Isaacson , Jobs took the PSU of Apple II, an advanced personal computer , and its developer, Rod Holt, very seriously. Jobs, according to Isaacson, stated the following:

Instead of the usual linear PSU, Holt created one that was used in oscilloscopes. He turned on and off the energy not 60 times per second, but thousands of times; this allowed him to save energy for much shorter periods of time, as a result of which he emitted much less heat. “This impulse PSU was as revolutionary as the Apple II logic board,” said Jobs later. - The kind is not often praised for this in history books, but should have been. Today, all computers use UPSs, and they are all copied from Rod Holt's circuit. ”

This serious statement did not seem to me too reliable, and I conducted my investigation. I found that although the UPSs were revolutionary, this revolution took place in the late 1960s and mid-1970s, when UPSs took over from simple but inefficient linear power supplies. Apple II, which appeared in 1977, received the benefits of this revolution, but did not cause it.

The correction of the Jobs version of events is not a trifle from the engineering field. Today, UPSs are the mainstay of everything; we use them daily to charge our smartphones, tablets, laptops, cameras, and even some cars. They feed the clock, radio, home audio amplifiers, and other small household appliances. The engineers who provoked this revolution deserve recognition. Anyway, this is a very interesting story.

A PSU in desktop computers, such as the Apple II, converts AC line current to direct current, and produces a very stable voltage to power the system. BP can be designed in many different ways, but most often there are linear and impulse circuits.

With all the warts

In the past, small electronic devices have commonly used bulky BP transformers, nicknamed "wall warts." At the beginning of the 21st century, technological improvements have allowed the practical application of compact, low-power switching power supplies to power small devices. With the drop in the cost of AC / DC switching adapters, they quickly replaced the bulky PSUs in most home devices.

Apple turned the charger into an ingenious device, introduced sleek charging for the iPod in 2001, inside which was a compact flyback converter controlled by integrated circuits (on the left in the picture). Soon USB charging became widespread, and the ultra-compact charger in the form of an inch cube from Apple, having appeared in 2008, became a cult icon (on the right).

The most fashionable high-level chargers of this type today use gallium nitride-based semiconductors that can switch faster than silicon transistors, and therefore are more efficient. Developing technologies in a different direction, today manufacturers offer USB-charging at a price less than a dollar, although at the same time saving on power quality and security systems.

* * *

A typical linear PSU uses a bulky transformer to convert a high-voltage AC outlet into a low-voltage AC, which is then converted to a low-voltage DC using diodes, usually four connected to a classic diode bridge circuit. Large electrolytic capacitors are used to smooth the output voltage of the diode bridge. Computer power supplies use a circuit called a linear stabilizer, which reduces the DC voltage to the desired level and keeps it at that level even with changes in the load.

Linear PSUs are trivial in design and creation. They use cheap low voltage semiconductor components. However, they have two big minuses. One is the need to use large capacitors and bulky transformers, which can never be crammed into something as small, light and convenient as the chargers that we all use for our smartphones and tablets. The other is a linear stabilizer circuit based on transistors that turns excessive DC voltage - anything above the required level - into stray heat. Therefore, such PSUs usually lose more than half of the energy consumed. And they often need large metal radiators or fans to get rid of this heat.

The UPS operates on a different principle: the AV line input turns into a high-voltage DC, which turns on and off tens of thousands of times per second. High frequencies allow the use of much smaller and lighter transformers and capacitors. A special circuit precisely controls the switching to control the output voltage. Since such power supplies do not need linear stabilizers, they lose very little energy: usually their efficiency reaches 80-90%, and as a result they are much less heated.

However, UPSs are usually much more complex than linear ones and more difficult to design. In addition, they put forward more requirements for components, and need high-voltage transistors that can efficiently turn on and off with high frequency.

I must mention that some computers used PSUs that were neither linear nor pulsed. One crude but effective technique was to power the motor from a power outlet and use it to spin up a generator that produced the required voltage. Motor generators have been used for several decades, at least since the advent of IBM machines with punched cards in the 1930s and until the 1970s, powering, among other things, Cray supercomputers .

Another option, popular from the 1950s and up to the 1980s, used ferroresonant transformers - a special type of transformer giving a constant voltage output. Also in the 1950s, a saturation inductor , a controlled inductor, was used to control the voltage of the tube computers. In some modern PSUs for PCs, it reappeared under the name of “ magnetic amplifier ”, giving additional regulation. But in the end, all these old approaches gave way to UPS.

The principles underlying the UPS have been known to electrical engineers since the 1930s, but this technology has rarely been used in the era of electronic tubes. At that time, in some BPs, special mercury lamps, thyratrons were used , and they can be considered primitive, low-frequency pulse stabilizers. Among them is the REC-30 , which fed the teletype in the 1940s, as well as the power supply unit for the IBM 704 computer from 1954. But with the advent of power transistors in the 1950s, UPSs began to improve rapidly. Pioneer Magnetics began producing UPSs in 1958. General Electric launched the early transistor UPS project in 1959.

In the 1960s, NASA and the aerospace industry became the main driving force in the development of UPSs, since for aerospace needs, the advantages of small size and high efficiency took precedence over great cost. For example, in 1962, the Telstar satellite (the first satellite to start transmitting television) and the Minitman rocket used UPSs. Years passed, prices fell, and UPSs began to be built into consumer equipment. For example, in 1966, Tektronix used UPSs in a portable oscilloscope, which allowed it to work both from a wall outlet and from batteries.

The trend accelerated as manufacturers began selling UPSs to other companies. In 1967, RO Associates introduced the first 20 KHz UPS, which it called the first commercially successful UPS. Nippon Electronic Memory Industry Co. began the development of standardized UPS in Japan in 1970. By 1972, most UPS manufacturers were selling UPS or preparing for their release.

Around this time, the computer industry began using UPSs. Early examples include the 1969 PDP-11/20 microcomputer from Digital Equipment, and the 1971 Hewlett-Packard microcomputer 2100A. A 1971 publication stated that among the companies using UPSs, all the major market players were noted: IBM, Honeywell, Univac, DEC, Burroughs, and RCA. In 1974, Nova 2/4 from Data General, 960B from Texas Instruments and systems from Interdata were noted in the list of microcomputers using UPSs. In 1975, UPSs were used in an HP2640A terminal, similar to IBM's Selectric Composer, and in an IBM 5100 laptop. By 1976, Data General had used UPSs in half of its systems, and HP in small systems such as 9825A Desktop Computer and 9815A Calculator. UPSs began to appear in home devices, for example, in some color TVs by 1973.

UPSs were often covered in electronic magazines of that era, both in the form of advertising and in articles. Back in 1964, Electronic Design recommended using a UPS because of its higher efficiency. On the cover of October 1971, Electronics World magazine featured a 500 W UPS, and the title of the article read: "Power supply with a pulse stabilizer." Computer Design in 1972 described in detail UPSs and their gradual capture of the computer market, although he also mentioned the skepticism of some companies. The 1976 Electronic Design cover read “Suddenly Switching Easier to Switch,” and described the new UPS control integrated circuit. Electronics magazine has a long article on this subject; Powertec had two-page promotional materials about the benefits of UPS with the slogan “The big switch is to switchers” [big changes for the switches]; Byte announced the release of UPS for microcomputers by Boschert.

Robert Boshert, who quit his job and started collecting power supplies in his kitchen in 1970, was a key developer of this technology. He concentrated on simplifying the circuits in order to make pulse PSUs competitive in price with linear ones, and by 1974 he had already produced inexpensive PSUs for printers in industrial quantities, and then in 1976 he also launched inexpensive 80W UPSs. K 1977 Boschert Inc. has grown to a company of 650 people. She made a power supply for satellites and a Grumman F-14 fighter, and later - computer power supplies for HP and Sun.

The advent of low-cost high-voltage high-frequency transistors in the late 1960s and early 1970s by companies such as Solid State Products Inc. (SSPI), Siemens Edison Swan (SES) and Motorola, helped bring the UPS into the mainstream. Higher switching frequencies increased efficiency, since the heat in such transistors was dissipated mainly at the time of switching between states, and the faster the device could make this transition, the less energy it spent.

The transistor frequencies at that time increased in leaps and bounds. Transistor technology developed so fast that the editors of Electronics World in 1971 could claim that the 500-watt PSU on the magazine cover could not have been produced just 18 months earlier.

Another notable breakthrough came in 1976 when Robert Mammano, co-founder of Silicon General Semiconductors, introduced the first UPS integrated circuit designed for electronic teletype. Its controller SG1524 drastically simplified the development of PSUs and reduced their cost, which caused a surge in sales.

By 1974, plus or minus a couple of years, it was clear to everyone, at least roughly understanding the state of the electronics industry, that there was a real revolution in BP designs.


Leaders and followers: Steve Jobs demonstrates the Apple II personal computer in 1981. First introduced in 1977, the Apple II has benefited from the industrial shift from bulky linear PSUs to small and efficient pulsed ones. But Apple II did not launch this transition, as Jobs later claimed.

The Apple II personal computer was introduced in 1977. One of its features was a compact UPS without a fan, which provided 38 watts of power and voltage of 5, 12, –5, and –12 V. He used a simple Holt circuit, a UPS with the topology of a flyback offline converter. Jobs stated that today every computer copies Holt's revolutionary circuit. But was this circuit revolutionary in 1977? And did every computer manufacturer copy it?

No and no. Similar flyback converters at that time were already sold by Boschert and other companies. Holt received patents for a couple of the features of his BP, but they were not widely used. And the creation of a control circuit of discrete components, as did for Apple II, turned out to be a technological dead end. The future of the UPS belonged to specialized integrated circuits.

If there was a microcomputer that had a long-term impact on the design of PSUs, it was IBM Personal Computer, launched in 1981. By that time, just four years after the release of Apple II, PSU technology had changed dramatically. And although both of these PCs used a UPS with the topology of a flyback offline converter and multiple outputs, that was all that was common between them. The power, control, feedback, and stabilization loops were different. And although the PSU for the IBM PC used an integrated circuit controller, it had almost twice as many components as the Apple II PSU. Additional components provided additional stabilization of the output voltage and the signal “quality power” when all four voltages were correct.

In 1984, IBM released a significantly updated version of the PC, called IBM Personal Computer AT. His PSU used many new schemes, completely abandoning the flyback topology. It quickly became the de facto standard and remained so until 1995, when Intel introduced the ATX form factor, which, like other things that determined the ATX PSU, remains the standard to this day.

But despite the advent of the ATX standard, computer power systems became more complicated in 1995 when the Pentium Pro appeared - a microprocessor that required less voltage and high currents than the ATX PSU could give directly. For this power supply Intel introduced a voltage regulation module (VRM) - a pulsed DC-DC converter installed next to the processor. He reduced 5 V from the power supply to 3 V used by the processor. The graphics cards of many computers also have VRM, which feeds the high-speed graphics chips installed in them.

Today, a VRM fast processor may require as much as 130 watts - much more than the half-watt power that the Apple II 6502 processor used. A modern processor alone can use three times more power than an entire Apple II computer.

The increasing energy consumption of computers has caused environmental concerns, resulting in initiatives and laws requiring more efficient PSUs. In the United States, the Energy Star and Industrial 80 Plus government certificates require manufacturers to issue greener PSUs. They manage to do this with the help of various technologies: more efficient standby power consumption, more efficient starting circuits, resonant circuits that reduce power losses in pulse transistors, active clamp circuits that replace pulse diodes with more efficient transistors. Improvements in the technology of MOSFET power transistors and high-voltage silicon rectifiers over the past ten years have also served to increase efficiency.

UPS technology continues to evolve in other ways. Today, instead of analog circuits, many vendors use digital chips and software algorithms that control the output. The development of the PSU controller has become both a matter of hardware design and a programming issue. Digital power management allows vendors to communicate with the rest of the system with greater efficiency and maintain logics. And although these digital technologies are mostly used in servers, they are beginning to influence the development of desktop PCs.

It is difficult to reconcile this whole story with Jobs's opinion that Holt should be known more widely, or that "Roda is not often praised for this in history books, but should have been." Even the best developers of BP do not become known outside the tiny community. In 2009, Electronic Design editors invited Boshert to his Engineering Hall of Fame . Robert Mammano received the Lifetime Achievement Award in 2005 from the editors of Power Electronics Technology. Rudy Severns received another such award in 2008 for UPS innovation. But none of these luminaries in the field of designing a PSU was even noted on Wikipedia.

Jobs's often-repeated view that Holt was undeservedly not noticed has led Holt's work to be described in dozens of popular articles and books about Apple, from Paul Quiotti's Rematch of the Nerds, which appeared in California magazine in 1982, to the biography of Jobs, the best-selling book Isaacson authored in 2011. So it’s ironic that although his work on Apple II wasn’t revolutionary at all, Rod Holt was probably the most famous BP developer of all time.