Some old systems where use an autotransformer with a few windings in the primary side. A simple comparator is measuring the rms value at the output with a reference and switches the windings (adding or removing them ) through a few triacs. There are available here on the market as Chinese products, mainly used for protecting the boiler systems. However, I will not use such thing for a computer. BTW, a good computer PSU -power supply unit (300 to 700W) has crowbar on the output. It's almost impossible to kill the motherboard even if the power voltage is with 20% higher on your system. I've repaired in old time a lot of such PSU, I almost dream how it works. Vasile On Thu, Nov 12, 2015 at 12:09 PM, wrote: > > Is a relay closure/opening fast enough for your application? > > Normally it is done by an SCR crowbar shorting the supply output, and the= n > relying on the supply over current protection to limit the current, or > mains protection fuse to blow. > > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .