On 9/28/2013 3:18 PM, Doug wrote: > On 09/28/2013 03:23 PM, Stan Hoeppner wrote: >> On 9/27/2013 6:37 PM, Joel Rees wrote: >>> On Fri, Sep 27, 2013 at 9:36 PM, Stan Hoeppner <s...@hardwarefreak.com> >>> wrote: >>>> A point I forgot to make. This is something everyone should know. >>>> >>>> Subject: The marketing myth of multiple +12V rails >>>> [...] >>> >>> What I want to know is why Intel CPUs still need the +12V. >> >> They don't now and they never did. The 8088 through 80486 and the first > > /snip/ > >> >> Installing two voltage regulators next to the CPU socket and using >> standard ~22 gauge copper wires from the 12V rail of the PSU solves the >> problem cheaply. The 12V rail was chosen because 3.6x less current is >> required vs using the 3.3V rail as was used previously, which means much >> smaller wires are needed. > /snip/ > > Do I understand correctly that there are two switching power supply > chips at the input to the CPU to produce 3.3Volts? Obviously, a linera > regulator cannot produce and gain in current. Iin = Iout for linear > regulators.
No, the switching in the PSU is done on the AC current before rectification, increasing the cycles from 60 Hz to 30-50 KHz. The high frequency AC, among other things, facilitates the conversion to DC, and allows for a much smaller transformer, though the output has ripple, unlike a battery, which provides true DC current. I'm thinking my attempt at a simple explanation of PSU design in my single vs dual rail rant was probably confusing, as it was technically inaccurate. Shame on me. The cost difference I was referring to is in the components that lay after the rectifier (which lay after the switching MOSFETs). This is mainly the regulator, which is also a MOSFET. With a single 12V rail design, the regulator FET is much larger and more expensive than the combined smaller FETs in a multi-rail design. However, another cost saving aspect to this I didn't mention previously is component commonality. If a vendor sizes it PSUs optimally, most if not every PSU in the line can use the same regulator FETs. For instance, a 25A regulator can be used for a single 12V rail for any PSU up to about 400W. For PSUs between ~400-700W there will be two 25A rails with two regulators. For PSUs above ~700W there would be three 25A rails, and so on. Since the same regulator is used in all models, this regulator can be acquired in much larger volume with a greater discount per unit. With single rail designs one would need to acquire 5 or more sizes of regulators which are progressively costlier per unit, and there is little or no volume discount relative to above. This is the major cost driver for the multi-rail designs, not simply the per unit cost of larger FETs. -- Stan -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/52477118.4020...@hardwarefreak.com
