I always feel thanks to all of the group members.

Today I'd like to ask some basic question (the group title is basic).
As is shown in the title, I don't exactly know why we use the PWM.
I think that all the works PWM can do can be done by the DAC and
linear
power amplifier. Of course, the price may be up. But then I am curious
again
that the price is the only reason for us to use the PWM scheme rather
than
analog scheme. Can anybody tell me the exact reason for the PWM.
Any kinds of Web site or material for studying shall be always
welcomed~!

On Oct 22, 9:31=A0pm, Gundal21 <hocheol....@gmail.com> wrote:
> I always feel thanks to all of the group members.
>
> Today I'd like to ask some basic question (the group title is basic).
> As is shown in the title, I don't exactly know why we use the PWM.
> I think that all the works PWM can do can be done by the DAC and
> linear
> power amplifier. Of course, the price may be up. But then I am curious
> again
> that the price is the only reason for us to use the PWM scheme rather
> than
> analog scheme. Can anybody tell me the exact reason for the PWM.
> Any kinds of Web site or material for studying shall be always
> welcomed~!

With linear control the pass element (usually some sort of transistor)
has to dissipate the unused power.  It dissipates the most at the one
1/2 power point.
An ideal pass element dissipates no power when it is full on.  So if
instead of turning it on at half power all the time you turn it on at
full power for 1/2 of the time, then you don=92t have to dissipate any
power in your pass element. (ideally).  This assumes that your load
doesn=92t mind having the power turned on and off=85 which is the case for
lots of things.

George H.

In article <33387dfc-de27-4f29-a2e7-
3...@v37g2000prg.googlegroups.com>, 
h...@gmail.com says...
> I always feel thanks to all of the group members.
> 
> Today I'd like to ask some basic question (the group title is basic).
> As is shown in the title, I don't exactly know why we use the PWM.
> I think that all the works PWM can do can be done by the DAC and
> linear
> power amplifier. Of course, the price may be up. But then I am curious
> again
> that the price is the only reason for us to use the PWM scheme rather
> than
> analog scheme. Can anybody tell me the exact reason for the PWM.
> Any kinds of Web site or material for studying shall be always
> welcomed~!

Two main reasons that I can think of:

1)The transistor that controls the current 
is either full-on or full-off. That means 
that the power/heat dissipated by the 
transistor itself is minimal. In a linear
circuit, at 50% speed, the motor and 
transistor dissipate half the power each.

2)PWM provides better torque at low speed;
the motor pushes hard for the brief periods
it's on.

I hope that makes sense!  :)

On Oct 22, 6:31=A0pm, Gundal21 <hocheol....@gmail.com> wrote:
> I always feel thanks to all of the group members.
>
> Today I'd like to ask some basic question (the group title is basic).
> As is shown in the title, I don't exactly know why we use the PWM.
> I think that all the works PWM can do can be done by the DAC and
> linear
> power amplifier.

I don't understand the question.  "DAC" means digital-to-analog
converter,
and "PWM" means pulse width modulation, which IS, often, exactly a
digital-to-analog conversion scheme.  So, PWM overlaps with DAC.
It isn't an either-or comparison here, at all!