Suppose I have a nice 18V output industrial/medical PSU. (But no worries this is for home.) And suppose I'm too cheap to buy that nice HDPLEX 200W 16V-24V input DC-ATX module, but on the other hand I'd also rather not have even the small amount of extra heat from the step-down conversion of 18V->12V inside the case. Let's say I have a 140W long term max. target. At 95% efficiency, that would mean 7W loss; or in a maybe more realistic 80W usage scenario that would be 4W.
And the mainboard already does step-down conversion from 12V with beefy multi-phase converters; so maybe 18V instead of 12V is not that much of a difference in practice?
If I get basic buck converter theory, the inductor ripple current would be just slightly higher when increasing the voltage 12V->18V, and the diode forward current would be like 0.5A larger in this case. So this doesn't look like something the mainboard's 12V step-down converter couldn't cope with easily, does it?
In this case a simpler DC-ATX module would be used, that simply passes through its input onto the 12V ATX rail, and does DC-DC conversion for the other ATX voltages. The module would need to be able to cope with 18V as well, of course. It would be also required that the mainboard's OVP, if it has one, doesn't trigger at 18V. For electrolytic caps 16V and 25V are standard voltage ratings, so better be 25V caps used.
I wonder what else I'm missing?
And the mainboard already does step-down conversion from 12V with beefy multi-phase converters; so maybe 18V instead of 12V is not that much of a difference in practice?
If I get basic buck converter theory, the inductor ripple current would be just slightly higher when increasing the voltage 12V->18V, and the diode forward current would be like 0.5A larger in this case. So this doesn't look like something the mainboard's 12V step-down converter couldn't cope with easily, does it?
In this case a simpler DC-ATX module would be used, that simply passes through its input onto the 12V ATX rail, and does DC-DC conversion for the other ATX voltages. The module would need to be able to cope with 18V as well, of course. It would be also required that the mainboard's OVP, if it has one, doesn't trigger at 18V. For electrolytic caps 16V and 25V are standard voltage ratings, so better be 25V caps used.
I wonder what else I'm missing?
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