Voltage regulator

[Wen Yen Chan]

Hello,

In most of the DC motor drive circuits I've played with the only filtering
between the controller and the motor was there to cut down the RFI. 
Generally the inductance of the motor coils and the inertia of the rotor
is enough to smooth out the pulsations. Due to the coil inductance and the
freewheeling diodes the current through the motor is fairly constant (at a
given setting) even though the input voltage may be turning on and off. The
average current through the motor's coils is roughly (the average input
voltage - the back EMF)/(DC coil resistance). The magnitude of the ripple
(pk-pk) is roughly ((Peak input voltage)-(back EMF)-(average current)*(DC
coil resistance))/(2*(switching freq)*inductance). The back EMF is
proportional to speed and motor flux.


On Sun, 3 Jan 1999, Tom Parker wrote:

> Greg Hermann <bearbvd at sni.net> wrote:
> 
> >>At 01:55 PM 1/2/99 -0500, you wrote:
> >>
> >>>
> >>>Hence, the proper answer of PWM.
> >>
> >>Exactly!
> >>The pump still sees full voltage, it just has it for a limited time!
> 
> >C'mon--the PWM switch LOWERS the AVERAGE voltage by switching teh FULL
> >voltage on and off rapidly. As I said, you want good smoothing of the
> >output, cuz the rapid pulsing IS what will dissassemble the windings!
> 
> Won't the smoothing system turn it into a lower constant voltage? If you have
> enough capacatance across it, it will just average out the pulses.
> 
> Or do you mean not this much smoothing, but enough to take the sharp edges of
> the transitions between on and off?
> 
> 
> --
> Tom Parker - tparker at nznet.gen.nz
>            - http://www.geocities.com/MotorCity/Track/8381/
> 
>