The future now

Progress in power supply design over the last quarter century has been fast and continuous. Among other factors, it’s been driven by component developments, market price reductions and new regulations – factors that, along with the relentless pressure for smaller products with higher efficiencies, show little sign of abating. Taking a backward glance at the ways in which power supplies have evolved over the last 25 years, Lambda UK’s technical director, Robin Jeffery said: “In the early 1980s, switchmode power supplies held sway over their linear counterparts, but customers needing more than one voltage in their systems would either need to buy a separate power supply for each voltage, or pay more for a customised multi-output supply.” A suitable alternative came in the form of the first modular power supplies. Typically 150W and 300W convection cooled units, they used a two FET forward converter operating at around 75kHz, which meant the power transformers and filtering components were quite large. “Mosfets had just been introduced and, whilst easier to drive than their bipolar counterparts, their high on state resistance meant power dissipation was high, a problem for high efficiency psu designs,” he continued. “In addition, most electrolytic capacitors were only rated for use up to 85ºC. These and other factors combined to limit the power densities that could be achieved to about 0.08W/cm³.” But the situation was to change dramatically.