Hi Wagner
thanks for the advice : )
regards
----- Original Message -----
From: Wagner Lipnharski <wagner@USTR.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, November 25, 1999 12:36 AM
Subject: Re: PWM speed control[OT]


> If you followed exactly the bipolar SGS example, apparently everything
> is ok.
>
> a) You should use the diodes.
>
> b) Check again all connections and possible "invisible short circuits"
> at your circuit board. Don't assume everything is ok just because you
> did it by yourself.  When I have a problem and can't find it, I go back
> to the basics, checking grounds, VCC's, logic levels, every single
> connection, check pin by pin in sequence, as if it was done by somebody
> else with an error in purpose to test you, suspect everything, don't
> assume things are correct. Changes of having a wrong connection, bad
> assembly or short circuit somewhere is just 99.99%, with 1 in 10
> thousand for a bad chip (except if you fried it).
>
> c) You can also try to use a 100 Ohms 10 Watts resistor, or use a 100 to
> 200 Watts (115Vac) normal incandescent lamp in place of the motor, and
> repeat the measurements.  The 200 Watts lamp should represent a
> resistance around 60 Ohms when lit, something less when not complete
> warm, mainly for DC supply, probably will drain around 1 Amp from the
> 30Vdc supply. If you are afraid to force too much the L298, use a 100 W,
> or even a 60W lamp instead.
>
> Wagner.
>
> soon lee wrote:
> >
> > ----- Original Message -----
> > From: Wagner Lipnharski <wagner@USTR.NET>
> >
> > Wagner wrote
> >
> > > If you are driving a transistor connected to ground, it means the
motor
> > > has one lead to VCC, than it seems to be an under driving  situation.
> > > This should be the reason why your voltmeter shows the same voltage no
> > > matter which pwm signal you use. The transistor is not switching
> > > completely to ground.  Why don't you show a simple schematic about
this
> > > driving design?
> > >
> > > Wagner
> >
> > the circuit that i have use is actually the circuit that is found in
> > appication note for L298/L293 (bi-direction)
> > the only thing thing i did not follow is tha used of diode at the output
and
> > the others all the same
> >
> > thanks for your help
> >
> > regards