WBO2 testing

[Glen Beard]

bcroe at juno.com wrote:
> 
> Measure the voltage across the lamp, and across the
> 1 ohm resistor.  If the lamp has less than 10 volts (and
> the LED is out), you are probably running in the curent
> limiting warmup mode.   The resistor will measure
> about 1.25 volt in that case.
> 
> You probably are using too large a lamp.  With a small
> voltage drop across the lamp and maximum current, you
> have a large voltage drop (at max current) across the
> LT1086.  This heating it up, apparently to the point of
> thermal shutdown which dims the light.
> 
> I would find a smaller bulb, which should run at 10 V
> with reduced voltage across the 1 ohm (crossover to
> voltage regulation).  A 2" by 3" heatsink is not very
> generous for this application, unless it has a lot of fins.

Thanks for the info.  How large of a heat sink do you
recommend?  Would a very small fan placed inside the project
case help?  This thing got way hotter than 100C and would
have easily melted the black plastic case had it not been
sitting out on the bench.  The data sheet says thermal
shutdown is around 165C.  I wonder if it really got that
hot...  The circuit drew about 1 amp for about a minute.

-- 
Glen Beard  95 T/A conv M6
355, Vortech, heads, cam...
http://home.nycap.rr.com/gbeard1/TransAm.html
http://home.nycap.rr.com/gbeard1/Impala/Impala.html

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