# How does a PC-Power Supply work? **URL:** \ **Category:** Factual Questions\ **Created:** [July 17, 2009, 10:34am UTC](https://boards.straightdope.com/t/how-does-a-pc-power-supply-work/503324 "2009-07-17T10:34:15Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Simple\_Mind](https://avatars.discourse-cdn.com/v4/letter/s/7cd45c/32.png) [@Simple\_Mind](https://boards.straightdope.com/u/Simple_Mind)\ **Post date:** [July 17, 2009, 10:34am UTC](https://boards.straightdope.com/t/how-does-a-pc-power-supply-work/503324/1 "2009-07-17T10:34:15Z")
Hi, i just bought a new Gigabyte Superb GE-P450P-C2 Power Supply for my new PC, i have been operating CB-Radio in the past and still have a 12Volt DC Power Supply it delivers 7 Amps nominal and 9 Amps peak, it also weights about 3 Kilos! Now the new Power Supply delivers 12 Volts DC and 18 Amps x2 and a lot of other Voltages and weights only about 1.2 Kilos, it also does not seem to have a Transformer inside, how does it work? ---
**Author:** ![zwede](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@zwede](https://boards.straightdope.com/u/zwede)\ **Post date:** [July 17, 2009, 11:47am UTC](https://boards.straightdope.com/t/how-does-a-pc-power-supply-work/503324/2 "2009-07-17T11:47:25Z")
Your new PSU is a Switching power supply. The key to the efficiency is that it creates an internal high-frequency wave form that can be transformed by a much smaller and lighter transformer. For (much more) detail there’s a nice article on Wikipedia: > **[Switched-mode power supply](https://en.wikipedia.org/wiki/Switching_power_supply)** > > A switched-mode power supply (switching-mode power supply, switch-mode power supply, switched power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. > Like other power supplies, an SMPS transfers power from a DC or AC source (often mains power, see AC adapter) to DC loads, such as a personal computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a s... ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 17, 2009, 1:28pm UTC](https://boards.straightdope.com/t/how-does-a-pc-power-supply-work/503324/3 "2009-07-17T13:28:29Z")
[QUOTE=zwede;11349153The key to the efficiency is that it creates an internal high-frequency wave form that can be transformed by a much smaller and lighter transformer.[/QUOTE] That’s only half the story. The other half is is the fact that a switching power supply regulates the output by modulating the switching itself. Because the transistors are either ON or OFF, they dissipate very little power, as opposed to your old “linear” power supply. In a linear power supply, the voltage regulation is achieved by continuously varying the transistor’s conduction, which turns any excess voltage into heat. The means that large heatsinks and large transistors are required. Since a switching power supply is so much more efficient, it can use much smaller transistors and heatsinks. ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [July 17, 2009, 6:06pm UTC](https://boards.straightdope.com/t/how-does-a-pc-power-supply-work/503324/4 "2009-07-17T18:06:35Z")
Note that switching power supplies may be less suitable for radio work because they in general or more RF noisy. I think this is less of a problem these days though. Brian ---
**Author:** ![zwede](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@zwede](https://boards.straightdope.com/u/zwede)\ **Post date:** [July 17, 2009, 6:38pm UTC](https://boards.straightdope.com/t/how-does-a-pc-power-supply-work/503324/5 "2009-07-17T18:38:50Z")
Good point. I once had an amplifier for my car that made radio reception impossible. I called the manufacturer of the amplifier and talked to one of their engineers who said the frequency of the switching power supply in that particular model tended to be in an “unfortunate” range. They replaced it with one of their other models that had a power supply with a slightly different frequency and then the radio worked fine.