On Nov 1, 2005, at 12:23 PM, Padu wrote:

> One VReg Advantages:
> - savings in power consumption
>
I don't think it's safe to assume that a single Vreg saves power.  First
of all, if you're using linear regulators, you're going to be 
dissipating
power proportional to your load current regardless of how many 
regulators
you have.  Only the "quiescent" power draw of the regulators is going to
add for each additional regulator, and if you're mostly going from 12V
to 5V, the power lost in regulation is going to dwarf Pq.  Using an
unregulated rail allows you to pick regulation technology appropriate to
each daughter card.  Low current cards can use simple and cheap linear
regulators.  A higher current card might opt for a switching regulator
to gain efficiency.  And some cards might benefit from having the 12V
available as well...

BillW
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