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From: dana@locus.com (Dana H. Myers)
Newsgroups: sci.electronics
Subject: Re: 80386.
Message-ID: <1991Jan16.214955.2836795@locus.com>
Date: 16 Jan 91 21:49:55 GMT
References: <1990Dec28.210731.10685@zoo.toronto.edu> <3340012@hpcvca.CV.HP.COM>
Organization: Locus Computing Corporation, Inglewood, CA
Lines: 32

In article <3340012@hpcvca.CV.HP.COM> scott@hpcvca.CV.HP.COM (Scott Linn) writes:
>/ hpcvca:sci.electronics / dana@locus.com (Dana H. Myers) / 12:51 pm  Jan 14, 1991 /
>
>>Power is given by:
>>
>>	P=IV		
>>
>>    Where:
>>	P = power in Watts
>>	I = current in Amperes
>>	V = voltage in Volts
>
>Right, and I = C * dv/dt, so P = C * V * dv/dt.
>
>In CMOS dv is equal to the supply (transitions are from supply to
>ground), so P = C * V^2 / dt.  But, 1/dt is the same as switching frequency,
>so Pdynamic = C * V^2 * f, not
>
>>	Pdynamic = V^2 * 2 * Pi * f * C,
>
>which gives you a value over 6 times larger than the actual power
>dissipation.

  Right. As I was writing the original posting, I was asking myself,
is this really correct? I looked it up, and, sure enough, the 2*Pi
component is incorrect. Of course, this does not affect the
discussion of the relationship of frequency and power consumption.

-- 
 * Dana H. Myers KK6JQ 		| Views expressed here are	*
 * (213) 337-5136 		| mine and do not necessarily	*
 * dana@locus.com		| reflect those of my employer	*