Thanks for the pointers Ruben. I would not be driving inductive load so I
may not require diodes. Point well taken.

Chetan Bhargava
http://microz.blogspot.com


On Sun, Oct 20, 2013 at 11:28 PM, Ruben J=F6nsson <maxruben@rjjournal.net>w=
rote:

> >
> > hFE doesn't matter much. My DC calculated load is around 350ma @ 12v DC=
;
> in
> > fact, I would be using PWM with variable duty cycle so the current will
> be
> > lower than calculated.
> >
>
> But if you are only going to use it as a digital switch and make sure tha=
t
> it
> is saturated when on and keeping the switching times as short as possible
> (as
> short time in the linear region as possible) the power dissipation over t=
he
> transistor will not be very high. 350mA @ around 0.5V saturation voltage
> gives
> 175mW (on continuously).
>
> I would probably use a hard driven N channel FET for PWM instead. And wou=
ld
> probably not need a heatsink either. If it is an inductive load, you migh=
t
> want
> to use external diodes (instead of the internal body diode in the FET) fo=
r
> back
> EMF.
>
> /Ruben
>
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> Ruben J=F6nsson
> AB Liros Electronic
> Box 9124
> 200 39 Malm=F6 Sweden
> www.liros.se
> Tel +46 40142078
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
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