Why do we use PWM control?
in [Basics]
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From: Gundal21 on 22 Oct 2009 21:31 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~!
From: George Herold on 22 Oct 2009 22:36 On Oct 22, 9:31 pm, Gundal21 <hocheol....(a)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 dont have to dissipate any power in your pass element. (ideally). This assumes that your load doesnt mind having the power turned on and off which is the case for lots of things. George H.
From: Randy Day on 22 Oct 2009 22:51 In article <33387dfc-de27-4f29-a2e7- 3a52101e1cbb(a)v37g2000prg.googlegroups.com>, hocheol.lee(a)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! :)
From: whit3rd on 24 Oct 2009 18:19 On Oct 22, 6:31 pm, Gundal21 <hocheol....(a)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!
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