Ower Supplies – just how far have we come?
Switch-mode power supply technology has developed over the years, particularly in efficiency and power density. More compact power conversion can help equipment designers make better use of limited enclosure space.
Compare power density using the exact model, operating load and thermal conditions rather than transferring the rating of one historical product to another.
Technological Advancement?
Early switch-mode power-supply development in the 1950s involved both vacuum-tube and transistor-based concepts. Rather than assigning a single first invention, this overview follows the technical move toward smaller and more efficient power conversion.
With this influx of technological advancement, designers were suddenly able to pick and choose from multiple components and multiple manufacturers, giving them an unprecedented number of options and potentially groundbreaking designs.
The focus of this intensive period of development was the traditional linear regulator – the brightest minds were trying to figure out how they could replace the outdated transformer and resistance method of changing input voltage with a more efficient design.
The idea they landed on used a transistor to chop the input voltage up with an average value less than the initial input (we have a fantastic store of technical articles here on the site if you’d like a more detailed description of SMPS operation).
With higher efficiency and fewer magnetic materials required, the new technology was smaller, lighter and generated less heat.
As with modern inventions with those characteristics, this 1950s solution was hugely appealing to businesses in a range of sectors – from electronics to aerospace and communications to computing, there was a flood of early adopters each jockeying to make the best use of this new power supply technology.
Calculating Power
During the 1970s, switching power conversion became useful in compact electronic equipment, where reducing power-supply size and weight mattered.
The same design priorities apply to computing equipment: a more efficient power stage can reduce transformer size, heat dissipation and the space required for cooling.
Similarly, aerospace manufacturers considering how they could save weight and space also began looking towards custom switching power supplies to create much more efficient designs.
Cooling Off in the ’70s and ’80s?
The 1970s was a busy decade once the initial breakthrough had been made and innovation continued at a very respectable pace. Several companies in UK, USA and Japan began to market standard power supply products.
Claims about who first commercialized the technology vary; this overview does not assign a single originator.
The electronics press of the era featured SMPS articles and advertisements as standard products became more widely available. Open-frame, enclosed and modular designs gave equipment builders alternatives to custom linear power stages.
The adoption of switching power supplies in personal computers helped designers pursue smaller and lighter systems. Cooling still depended on total losses, enclosure conditions and component limits: some designs relied on convection, while others used fans, including fan-cooled ATX-style arrangements.
In the late 1980s and early part of the 1990s, industry-standard 3 x 5” power supplies became available with an auto-ranging input that sensed whether it was connected to 120VAC or 230VAC and adjusted accordingly. These products had powers of 25 – 40W, or 1.66 to 2.66W/In2
EU Shakeup
As more and more companies entered the market, some loose industry standards appeared around common sizes like 3×5”. Power densities began to improve as advances in magnetics, switching transistors and controller ICs progressed. These changes offered higher efficiencies and made better power densities possible.
