Re: Is 3.3v supplied by motherboards?

["Tom Hicks" <thicks@fore.com>]

> 
> I am designing an expansion card that uses a mix of 5v and 3.3v parts. My
> questions are:
> 
> 1) Should I derive 3.3v through a regulator on my board or is 3.3v
available
> from the motherboard?
> 
> 2) If 3.3v is available, is it available on all motherboards or only
some? 
> 
> 3) If 3.3v is available, which type of connector do I use? 5v, 3v, or
universal?
> 

1.  Derive 3.3V with a regulator (unless you are designing for a
specialized
    market, where you can guarantee all the motherboards/backplanes you
will
    operate with supply 3.3V)

2.  3.3V is available from the motherboard in some systems.  A survey
    of machines in my department yields about 25% providing 3.3V power.

3.  If you are designing a 5V or a universal card, you need to regulate
3.3V.
    If you are designing a 3.3V card, you do NOT need to regulate 3.3V from
    the 5V supply.

Tom
--
Tom Hicks			Fore Systems
Design Engineer			174 Thorn Hill Rd
Adapter Group			Warrendale, PA 15086
thicks@fore.com	

¹˜†