Theoretically, no power gets wasted, although in practice the efficiency will be 80%-90%.
In a switching power supply, the AC line input is converted to high-voltage DC, and then the power supply switches the DC on and off thousands of times a second, carefully controlling the time of the switching so the output voltage averages out to the desired value.
#MAC PRO POWER SUPPLY DIFFERENCES 2012 2009 PLUS#
On the plus side, the components (other than the transformer) in linear power supplies only need to handle low voltages and the output is very stable and noise-free.Ī switching power supply works on a very different principle: rapidly turning the power on and off, rather than turning excess power into heat.
The second disadvantage is they are large and heavy. One big disadvantage however, is they typically waste about 50-65% of the power as heat, often requiring large metal heat sinks or fans to get rid of the heat. Linear power supplies are almost trivial to design and build. The linear regulator is an inexpensive easy-to-use transistor-based component that turns the excess voltage into waste heat to produce a stable output. )Ī typical linear power supply uses a bulky power transformer to convert the 120V AC into a low AC voltage, converts this to low voltage DC with a diode bridge, and then uses a linear regulator to drop the voltage to the desired level. Mechanical motor-generator systems and ferroresonant transformers. (See the notes for more about obsolete technologies such as large Power supplies can be built in a variety of ways, but linear and switching power supplies are the two techniques relevant to this discussion. In a standard desktop computer, the power supply converts AC line voltage into DC, providing several carefully regulated low voltages at high currents. The credit for this revolution should go to advances in semiconductor technology, specifically improvements in switching transistors, and then innovative ICs to control switching power supplies. There was, in fact, a revolution in power supplies in the late 1960s through the mid 1970s as switching power supplies took over from simple but inefficient linear power supplies, but this was a few years before the Apple II came out in 1977. While most people view the power supply as a boring metal box, there's actually a lot of technological development behind it. The history of switching power supplies turns out to be pretty interesting. It turns out that Steve Jobs was making his customary claim that everyone is stealing Apple's revolutionary technology, entirely contrary to the facts. Modern computer power supplies are totally different and do not rip off anything from Rod Holt's design.
It turns out that Apple's power supply was not revolutionary, either in the concept of using a switching power supply for computers or in the specific design of the power supply. I found it amazing to think that computers now use power supplies based on the Apple II's design, so I did some investigation. Every computer now uses switching power supplies, and they all rip off Rod Holt's design." "Rod doesn't get a lot of credit for this in the history books but he should. "That switching power supply was as revolutionary as the Apple II logic board was," Jobs later said. It switched the power on and off not sixty times per second, but thousands of times this allowed it to store the power for far less time, and thus throw off less heat. Instead of a conventional linear power supply, Holt built one like those used in oscilloscopes. Steve Jobs contains a remarkable claim about the power supply of the Apple II and its designer Rod Holt: