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'[PIC]: 10 PWM outputs on 16F874'
2000\08\24@033643 by Vasile Surducan

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>Hi,Thanks everybody.I did not imagine that audio problem is also
>involved. I have to checkthis out.Rgdsramana

  Audio it's not a problem. PWM frequency either !
  At 100mA and 13V you may filter the PWM and
use a nice and fine DC level. The greateast frequency is
the smaller capacitor you need. Simple.
  Vasile
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Surducan Vasile
email:spam_OUTvasileTakeThisOuTspaml30.itim-cj.ro
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2000\08\24@101240 by Olin Lathrop

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> >Hi,Thanks everybody.I did not imagine that audio problem is also
> >involved. I have to checkthis out.Rgdsramana
>
>    Audio it's not a problem. PWM frequency either !
>    At 100mA and 13V you may filter the PWM and
> use a nice and fine DC level. The greateast frequency is
> the smaller capacitor you need. Simple.

Not so simple.  You don't want to tie capacitors to the PWM output drivers.
That would cause large currents and excessive losses every time the
switching components (FETs usually) are switched.  You could do an LPF with
a resistor or inductor in series with the PWM drive output with a cap
accross the load.  However, the resistor scheme creates loss, and the right
inductor usually needs to be too large to be practical.  I'm not saying you
should never filter a PWM power output, just that it's definitely not
simple, and not something I would recommend as a starting design for someone
new to this sort of thing.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, .....olinKILLspamspam@spam@cognivis.com, http://www.cognivis.com

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2000\08\25@051253 by Vasile Surducan

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>>    Audio it's not a problem. PWM frequency either !
>>    At 100mA and 13V you may filter the PWM and
>> use a nice and fine DC level. The greateast frequency is
>> the smaller capacitor you need. Simple.

>Not so simple.  You don't want to tie capacitors to the PWM output
>drivers.

 Who thought at such a crazy thing?

{Quote hidden}

 You may say that ! It's correct. But why to swich with expensive
FET's only max 1...1.5VA when you may filter the output PWM from
PIC with a simple RC filter, obtain a nice DC level and polarize an
darlington transistor which will drive the motor. Like I said: easy
At 1/4 from full power transistor will dissipate near 1VA.

>just that it's definitely not
>simple, and not something I would recommend as a starting design
>for someone
>new to this sort of thing.

 I've already done this and works fine ! Best result's with high PWM
frequency. Of course not applicable at high power motors.


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2000\08\25@052919 by Ramana

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Hi, Vasille
Is it possible for you to provde a indicative ckt for your approach.
Especially the darlington drive ckt in the output stage.
rgds
ramana


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