Chip operating temperatures

[Krister Wikstrom]

>Just think of the power dissipation from four coil drivers at say
>40% dutycycle at 6000 rpm (dwell =3D 4mS/Wasted-Spark) and say eight
>injector drivers at 75% dutycycle at 6000 rpm (Fuel p/w =3D 15mS/SEFI)
>Typically, a 4 cylinder ECU can be sucking up to 10 Amps when the
>engine's really revving, I don't have figures to hand for 8 cylinder
>systems and of course all these figures depend on coil/injector type
>and so on, but we're still talking about passing a lot of current
>through the system. 120 watts can have pretty serious heating effects
>on the box especially if it's mounted in an area of static airflow.

 =20
I think the 120W is not dissipated at the driver location, most goes to =
the injectors. If the driver sinks 10A
and drops maybe 0.6V, the "warming" power is 6W - right? Using some low =
RDSon MOSFETs etc. may have even lower voltage drop and power =
dissipation.

I've been repairing some (low cost) car audio stuff, and there seems to =
be a lot of 0-70 C components used. This
is a matter of cost, and those seem to survive/work at least on cold. On =
the other hand, they _did_ broke down...
(usually by too low speaker impedance or shorts, cheap stuff seem to =
have no good protection circuits).


  Krister Wikstrom
  kwi at mamma.icl.fi