-=> Mike Ross said to Greg Mayman
 -=> about "VEHICLE LED'S" on 09-29-03  00:15.....

 MR> {at}PID: BWMAX2 3.20 [Reg]
 MR> {at}MSGID: 1:167/133.0 3f77b47d
 MR> "Greg Mayman" bravely wrote to "Mike Ross" (26
Sep 03  08:03:00)
 MR> --- on the heady topic of "VEHICLE LED'S"
 
 GM> But I was debating whether the lamp filament subjected to a
 GM> changing input voltage approximated more to constant power (as
 GM> you claimed) or constant current.

 MR> What I tried to explain was that the power change was less than the
 MR> current change.

Which is a mathematical impossibility.

Since power is voltage times current, then if they both go up,
power must ALWAYS go up faster than either of them.

It can never go up at a lesser rate than either factor unless one
of the factors is going down.

Let's look at the current and power versus voltage from your
table. I have added three extra columns that show the increase
in voltage (d-V), current (d-I) and power (d-P) from the previous
step.

 % rated V  %Current  % Power     d-V       d-I     d-P
 ----------------------------
   60         75        45
   70         81        57       +16.7%    +8.0%    +26%
   80         88        70       +14.3%    +8.6%    +22%
   90         94        85       +12.5%    +6.8%    +21%
  100        100       100       +11.1%    +6.3%    +18%
  110        106       117       +10.0%    +6.0%    +17%
  120        113       136       + 9.1%    +6.6%    +16%
  130        119       155       + 8.3%    +5.3%    +14%

It is obvious that the power change is about THREE TIMES the
current change.

The lamp is a lot closer to a constant current load with changing
voltage (as I said) than it is to a constant power load, which is
what you were claiming.

From Greg Mayman, in beautiful Adelaide, South Australia
   "Queen City of The South"    34:55 S  138:36 E

... He who says it can't be done shouldn't interrupt those doing it.
___ Blue Wave/386 v2.30

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