Archived from groups: alt.comp.periphs.mainboard.asus (More info?)
In article <419E9D4B.8030404@neo.rr.com>, WatzmanNOSPAM@neo.rr.com
says...
> I suspect that what you think is happening, really isn't.
>
> If you are getting 5 volts from a 7805 whose input is 24 volts, there is
> 19 volts across the 7805. That's not speculation or theory -- it's
> simple physics, e.g. it's both theory AND real-world practice.
>
> If you are pulling 500ma through ANY device with 19 volts across it,
> it's GOING to dissipate 9.5 watts. Again, that's not speculation or
> theory -- it's simple physics, e.g. it's both theory AND real-world
> practice.
>
> You can't dissipate 9.5 watts in a device the size of a 7805 without
> some serious thermal considerations (and you may not be able to do it at
> all, period).
>
> My suggestion is that either the voltage or the current are not what you
> say they are (or even believe that they are), or that you are just
> making this up and have not really tried it.
>
> [which, among other things, leaves me wondering if you know how to use a
> multi-meter, especially to measure current]
Rather than argue with me, try it yourself, as I've suggested many times
in this thread. I was doing this in the early 80's for a living, have
used a scope and meter since the late 70's, and am a little tired of
people saying that something can't or doesn't work when they are only
willing to quote the spec sheet back at me. I'll say it again, 24vdc
supply to a LM7805 with heat sink, producing 5v out, and at a 500ma load
on the 5v side. Working for years. If you don't try it for yourself then
then you can't really say much about it.
--
--
spamfree999@rrohio.com
(Remove 999 to reply to me)
In article <419E9D4B.8030404@neo.rr.com>, WatzmanNOSPAM@neo.rr.com
says...
> I suspect that what you think is happening, really isn't.
>
> If you are getting 5 volts from a 7805 whose input is 24 volts, there is
> 19 volts across the 7805. That's not speculation or theory -- it's
> simple physics, e.g. it's both theory AND real-world practice.
>
> If you are pulling 500ma through ANY device with 19 volts across it,
> it's GOING to dissipate 9.5 watts. Again, that's not speculation or
> theory -- it's simple physics, e.g. it's both theory AND real-world
> practice.
>
> You can't dissipate 9.5 watts in a device the size of a 7805 without
> some serious thermal considerations (and you may not be able to do it at
> all, period).
>
> My suggestion is that either the voltage or the current are not what you
> say they are (or even believe that they are), or that you are just
> making this up and have not really tried it.
>
> [which, among other things, leaves me wondering if you know how to use a
> multi-meter, especially to measure current]
Rather than argue with me, try it yourself, as I've suggested many times
in this thread. I was doing this in the early 80's for a living, have
used a scope and meter since the late 70's, and am a little tired of
people saying that something can't or doesn't work when they are only
willing to quote the spec sheet back at me. I'll say it again, 24vdc
supply to a LM7805 with heat sink, producing 5v out, and at a 500ma load
on the 5v side. Working for years. If you don't try it for yourself then
then you can't really say much about it.
--
--
spamfree999@rrohio.com
(Remove 999 to reply to me)
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