Hi Mike
On (21 Nov 97) MIKE ROSS wrote to Alec Cameron...
 AC> That word of yours "drop" annoys me. It ain't a drop, it is an
 AC> opposing emf. I baulk at the impression that the diode is wasting
 AC> energy, as would an "ohmic" ie resistive device. Getting hot!
 AC> It is behaving instead, as a bucking ie subtractive voltage, and
 MR> stays
 AC> cool with it.
 MR> I'd like to live in that utopia where rectifier diodes have an "emf" and
 MR> never get hot... :-)
OK it runs less hot! The heat dissipation [watts] within a diode is not I
think, equal to E times I. Yes there is an ohmic energy loss, yes it gets hot
but it is less hot than volts times amps would propose.
 MR> Alec, if you read a little about P-N junctions on Fermi levels, energy
 MR> band gaps, conduction bands, depletion layers, contact potentials,
 MR> recombination sites, saturation currents, and electron/hole mobility in
 MR> semi-conductor junctions, you'll change your mind in that rectifier
 MR> diodes do indeed dissipate energy by emitting infra-red photons.
All too technical for me! I am victim to the tech education curriculum of the
1940s. *Of course* diodes release energy [why else have a heat sink!] but I 
had
to endure hours of circuit theory and circuit analysis- remember Thevenin's
Theorems? and in assembling Equivalent Circuits we had *ALWAYS* to insert a
fixed *opposing EMF* at every diode. Maths is of course a FAKE, but it 
eaches
one a practical language without which we may not converse usefully with the
skilled.
*OPPOSING EMF* is a common enough concept, it is defined for example in elec
machines and for motors, is given as the reason for the load amps decreasing
as the speed rises. The motor power input is thus figured from the ratio of
[difference between applied and opposing v] to the line amperes, rather than
the ratio of applied v to line amperes.
As students we despised some of the artful dodges laid on us by tech 
eachers.
To the classical math processes of Addendo and Dividendo we added Fakendo.
There is still a lot of that about! ;-)
Are you happy with the circuit characteristics known as negative sequence
resistance;  quadrature axis subtransient reactance; imaginary numbers;
excessive voltage rise along a heavily loaded transmission line?
The corrupt defining of characteristics and terminology, doesn't stand up to
scholarly analysis but boy! it may help get the job done and that is how I 
as
employed. Omlettes need broken eggs :-)
        
 MR> Hmmm... which reminds me you may be able to recover some of the
 MR> rectifier's losses by placing it in front of the solar panels?
Or soft boil an egg in the teapot.  Cheers....ALEC
ALZHEIMERS-    New friends every day!
... ......Pavlov Had a Dog
--- PPoint 1.92
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