Author: leventkomurcu@gmail.comDate: 04:08 24-12-06
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Hi all,
Thanks for everything that you write before i have learnd a lot of from
this group.
I am designing a circuit which uses a 18f452 and DAC0800 for analog
output. Each DAC drives an TIP31 type BJT. Could we use this analog
signal to control a DC motors speed? will this be efficent as PWM ? If
not so why not ?:)
Thanks for reply?
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Author: Andrew HolmeDate: 05:04 24-12-06
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<leventkomurcu@gmail.com> wrote in message
news:1166951325.192398.295500@a3g2000cwd.googlegroups.com...
> Hi all,
>
> Thanks for everything that you write before i have learnd a lot of from
> this group.
>
> I am designing a circuit which uses a 18f452 and DAC0800 for analog
> output. Each DAC drives an TIP31 type BJT. Could we use this analog
> signal to control a DC motors speed? will this be efficent as PWM ? If
> not so why not ?:)
>
> Thanks for reply?
>
It would not be as efficient as PWM. Power would be dissipated in the BJT.
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Author: John PopelishDate: 10:19 24-12-06
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leventkomurcu@gmail.com wrote:
> Hi all,
>
> Thanks for everything that you write before i have learnd a lot of from
> this group.
>
> I am designing a circuit which uses a 18f452 and DAC0800 for analog
> output. Each DAC drives an TIP31 type BJT. Could we use this analog
> signal to control a DC motors speed? will this be efficent as PWM ? If
> not so why not ?:)
To a first approximation, the speed of a DC permanent magnet
motor is proportional to the voltage across it. The two
most common ways to provide a variable voltage to a motor
are linear and PWM regulation. Linear regulation starts
with the highest voltage you will need, and burns the extra
voltage, at slow speeds, as drop across some variable
resistance device (i.e. transistor). A PWM regulator lowers
the voltage by switching it to zero part of the time, and
averaging the result over time. It is noisier and more
complicated than linear regulation, but involves no
intentional energy waste.
The PIC18F452 includes two PWM pulse generators
(programmable total cycle time, and programmable duty
cycle). All you need to add to those outputs is a switch
(mosfet of transistor, catch diode, and possibly some filter
components and isolation between motor supply and
processor supply) capable of translating the pulses up to
the required voltage and current needed by the motor.
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Author: JamieDate: 10:20 24-12-06
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leventkomurcu@gmail.com wrote:
> Hi all,
>
> Thanks for everything that you write before i have learnd a lot of from
> this group.
>
> I am designing a circuit which uses a 18f452 and DAC0800 for analog
> output. Each DAC drives an TIP31 type BJT. Could we use this analog
> signal to control a DC motors speed? will this be efficent as PWM ? If
> not so why not ?:)
>
> Thanks for reply?
>
You can use it how ever, it won't be efficient in power use wise and
it will generate some heat when throttled back.
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Author: pLaNiXDate: 12:35 24-12-06
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Ok i got it. i have some coding/compiler difficulties using multiple
pwm outputs (sending the PID output to a 8 bit port seemed a bit more
easy to me :)) but the using PWM output (CCP1 CCP2A) is the best
sollution as you said.
Thanks for *all* replies you cleared my mind. :)
John Popelish wrote:
> leventkomurcu@gmail.com wrote:
> > Hi all,
> >
> > Thanks for everything that you write before i have learnd a lot of from
> > this group.
> >
> > I am designing a circuit which uses a 18f452 and DAC0800 for analog
> > output. Each DAC drives an TIP31 type BJT. Could we use this analog
> > signal to control a DC motors speed? will this be efficent as PWM ? If
> > not so why not ?:)
>
> To a first approximation, the speed of a DC permanent magnet
> motor is proportional to the voltage across it. The two
> most common ways to provide a variable voltage to a motor
> are linear and PWM regulation. Linear regulation starts
> with the highest voltage you will need, and burns the extra
> voltage, at slow speeds, as drop across some variable
> resistance device (i.e. transistor). A PWM regulator lowers
> the voltage by switching it to zero part of the time, and
> averaging the result over time. It is noisier and more
> complicated than linear regulation, but involves no
> intentional energy waste.
>
> The PIC18F452 includes two PWM pulse generators
> (programmable total cycle time, and programmable duty
> cycle). All you need to add to those outputs is a switch
> (mosfet of transistor, catch diode, and possibly some filter
> components and isolation between motor supply and
> processor supply) capable of translating the pulses up to
> the required voltage and current needed by the motor.
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Author: John PopelishDate: 12:52 24-12-06
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pLaNiX wrote:
> Ok i got it. i have some coding/compiler difficulties using multiple
> pwm outputs (sending the PID output to a 8 bit port seemed a bit more
> easy to me :)) but the using PWM output (CCP1 CCP2A) is the best
> sollution as you said.
>
> Thanks for *all* replies you cleared my mind. :)
If you run out of PWM outputs, there are simple ways to take
the analog voltage output from a DAC and use a comparator to
produce a PWM output that produces a motor voltage
proportional to the DAC voltage. But it certainly is not a
simple as using the firmware PWM output.
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Author: DorianDate: 13:23 26-12-06
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. Could we use this analog
> signal to control a DC motors speed? will this be efficent as PWM ? If
> not so why not ?:)
>
An added benefit of PWM control is smoother starting of motors. Usually a
motor driven by an analog voltage has to be overdriven to overcome starting
friction and then throttled back to prevent over-speeding. This is not a
problem in PWM control.
Dorian
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