Hi Imre.

I thought I already fixed my "invention" in followed up message.
The idea of 45W somehow dissipated on TO-220 didn't let me sleep
all that nite ;)

WBR Dmitry.


"dr. Imre Bartfai" wrote:
>
> Hi Dimitriy,
>
> maybe I have missed something very important, but AFAIK
>
> P = dU * Iout + Uin * Ignd = 6 * 1.2 + 18 * 0.008 = 7.344 Watt
>
> This, in turn, is more than enough to cook a TO220. I guess the 45W you
> calculated would blow the regulator immediately. Or am I wrong here?
>
> Regards,
> Imre
>
> On Tue, 15 Jul 2003, Dmitriy A. Kiryashov wrote:
>
> > Hi Barry.
> >
> > In that case I would say that the power dissipated by regulator is:
> >
> > P = dU^2 * Iout + Uin^2 * Ignd = (Uin_max - Uout)^2 * Iout + Uin^2 * Ignd;
> > where Iout = 12v / 10R = 1.2A and Ignd ~= 0.008A
> >
> > (18max - 12out)^2 *1.2 + 18^2 *0.008 ~= 45.8W  which is slightly higher
> >
> > (not counting that 14.4W disssipated on that resistor ;)
> >
> >
> > WBR Dmitry.
> >
> >
> >
> > Barry Gershenfeld wrote:
> > >
> > > I hope the drawing really meant to show the 10 ohm resistor on
> > > the output of the 7812 because in the picture I got, nothing
> > > is connected to the output.
> > >
> > > >From what you say I would guess that that one board has a short
> > > circuit, that the resistor is grounded, and your 7812 is
> > > trying to supply 12 volts across 10 ohms.
> > >
> > > P=E*E/R = 12 * 12 / 10 =  14 Watts.  Hot enough!
> > >
> > > Or maybe the wiring or the motor is shorted.
> >
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