| Science Forum Index » Electronics - Basics Forum » Why do we use PWM control?... |
|
Page 1 of 1 |
|
| Author |
Message |
| Gundal21... |
 Posted: Thu Oct 22, 2009 3:31 pm |
|
|
|
Guest
|
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~! |
|
|
| Back to top |
|
|
|
| George Herold... |
| Posted: Thu Oct 22, 2009 4:36 pm |
|
|
|
Guest
|
On Oct 22, 9:31 pm, Gundal21 <hocheol.... at (no spam) gmail.com> wrote:
[quote]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~!
[/quote]
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’t have to dissipate any
power in your pass element. (ideally). This assumes that your load
doesn’t mind having the power turned on and off… which is the case for
lots of things.
George H. |
|
|
| Back to top |
|
|
|
| Randy Day... |
| Posted: Thu Oct 22, 2009 8:51 pm |
|
|
|
Guest
|
In article <33387dfc-de27-4f29-a2e7-
3a52101e1cbb at (no spam) v37g2000prg.googlegroups.com>,
hocheol.lee at (no spam) gmail.com says...
[quote]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~!
[/quote]
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!  |
|
|
| Back to top |
|
|
|
| whit3rd... |
| Posted: Sat Oct 24, 2009 12:19 pm |
|
|
|
Guest
|
On Oct 22, 6:31 pm, Gundal21 <hocheol.... at (no spam) gmail.com> wrote:
[quote]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.
[/quote]
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! |
|
|
| Back to top |
|
|
|
|
