I am just wondering whether it would not be better to do some sort of AC
detection + PWM on the mains power 220VAC and then just rectify it to be
used for the DC motor. That will sort out my problem with the DC voltage
being too high. Isn't there an APPnote about this somewhere on the Microchip
website?


Proposed circuit:


    220VAC ---------> PWM -------> rectifier -------->DC Motor
                       |
                             |
                             |
                          Pic uC


Thanks

Kevin



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Kevin Howell
Sent: 14 April 2002 07:22 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]:High power DC switching..


I am not using a transformer, I'm using our mains supply which is 220VAC...

Question: Will the very nature of PWM on the motor not cause the average
voltage to drop below the accepted range in any case? Then I just have to
make sure I don't switch the motor on at 100% duty cycle.

Thanks!
Kevin


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Sean H. Breheny
Sent: 14 April 2002 05:31 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]:High power DC switching..


Hi Olin,

I think he means a full wave rectifier using two diodes and a center-tapped
transformer, to give half voltage.

Sean

At 07:55 PM 4/13/02 -0400, you wrote:
> > > Something else bothers me a bit. I have just read through the spec of
>the
> > > motor and I don't think this motor can handle more than 220V DC. Our
>mains
> > > supply is 220V Ac. Putting that through a bridge rectifier and a cap
>will
> > > probably push it to 320 V DC!! which is miles to much. What can I do
to
>get
> > > this down to around 200V DC again?
> >
> > You could use a half-bridge rectifier -- two diodes instead of four.
>
>You could, but you'd still end up with the same maximum voltage.  It would
>just droop more between the peaks.
>
>
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