Re: L298 goes boom ( It's Fixed!- Yeah! )

One of the great "gotcha's" in electronic design is the removal of
heat from active components. All the ratings on the components are
at lower temp ratings and have to be heavily derated for each degree
of C above that nominal amount. Lets take the case of the poor
7812. It has to put out 12VDC of regulated voltage at up to 1A. It
has 38VDC Input so that means we have to dissipate the other 26Volts
as heat (26V * 1A = 26Watts). All of that heat is concentrated in
the die of the chip and thermally has to get from there out to the
mounting tab and from there out to the heatsink and from there out to
the surrounding air. If you cannot get 14 to 16VDC @ 1 AMP from
another source I would recommend you use a DC to DC switcher module.
They are available from a varity of surplus dealers: Marlin P. Jones
(www.mpja.com) or BGMicro (www.bgmicro.com) to name a couple. You
can get multiple output units that have 12 and 5 volt regulated
outputs and they run cool. At the very least those regulators need
some pretty good heatsinking themselves. The 78XX series is supposed
to have its own thermal shutdown and shorted output protection but I
doubt you want to loose critical voltages on the middle of a cut!

The amount of heat dissipated in a switching module like the l298 is
dependent on the head voltage and the efficiencies of the internal
devices. Hopefully they are optimized with quick turnon and turnoff
times at the switching frequency. Turning off a semiconductor slowly
(more than a few microseconds) leaves the device in a linear range
(the difference between controlling a 100W light bulb with a switch
versus a pot) and causes excessive heat losses. There are other
factors as well. You have to trust the chip designer since you have
little access to internal switching components. Needless to say that
the goal is to keep the internal die cool and if there is not good
thermal conduction between the heatsink and the device you may still
be able to put your hand on the heatsink and fry the chip! The
movement of air across the surface of the heatsink (BETWEEN the fins)
will make a big difference in how much heat can get dissipated.

--- In CAD_CAM_EDM_DRO@y..., "tauscnc" <tauscnc@h...> wrote:
> Hey Afogassa,
> Man sounds like your really having trouble keeping them cool. I
would
at the edge of the board it would be easy<snip>.