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'[EE]: Generating an isolated 0-10Vdc voltage'
2002\11\28@194413 by Peter Homann

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Hi,

I'm planning to generate a 0-10V analog voltage using the PIC PWM, RC
filter, and op-amp.

The question is how do I isolate the output voltage. The voltage is to drive
a 90V DC motor controller where the controller ground is live.

One solution is to opto-isolate the inputs to the PIC and have the whole
circuit live. I would have to power the PIC circuit via a 12V zener and
resistor.

The other option is to isolate the 10V signal via a transformer. Does anyone
have experience with this or other alternatives?

Thanks,


Peter Homann
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250 Bay St, BRIGHTON, 3186, AUSTRALIA
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2002\11\28@195449 by Wouter van Ooijen

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> The question is how do I isolate the output voltage. The
> voltage is to drive
> a 90V DC motor controller where the controller ground is live.

Use a dual optocoupler. I don't know what the term is for this circuit,
but the second coupler is put in the feedback loop on the HV side to
make the transfer independent of the coupler's characteristic, provided
that the two couplers have the same characteristic.

Or (avoid the problem instead of solving it) put the PWM signal through
an optocoupler (or trafo), do the filtering on the HV side.

Wouter van Ooijen

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2002\11\28@200822 by Peter Homann

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Thanks for the reply,

The 2nd option sounds OK. I'll still need to create a 12Vdc supply for the
filter circuit and opamp buffer.

Any other suggestions for generating the 12V supply from the 120Vac input.
My plan is to use a Zener and series power resistor to drop the voltage.


Peter Homann
.....Peter.HomannKILLspamspam@spam@adacel.com
Adacel Technologies Limited,
250 Bay St, BRIGHTON, 3186, AUSTRALIA
http://www.adacel.com <http://www.adacel.com>
Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960
Mobile 0421-601 665


{Original Message removed}

2002\11\29@002057 by Chris Hunter

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Try a capacitor dropper, rather than the resistor to feed your zener -
you'll get less heat.

Chris

----- Original Message -----
From: "Peter Homann" <peter.homannspamKILLspamADACEL.COM>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Friday, November 29, 2002 1:07 AM
Subject: Re: [EE]: Generating an isolated 0-10Vdc voltage


{Quote hidden}

> {Original Message removed}

2002\11\29@002524 by Peter Homann
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Hi Chris,

Thanks for the reply. I haven't heard of a capacitor dropper. Any
suggestions on the size of capacitor or reference circuit.

Thanks,


Peter Homann
Peter.Homannspamspam_OUTadacel.com
Adacel Technologies Limited,
250 Bay St, BRIGHTON, 3186, AUSTRALIA
http://www.adacel.com <http://www.adacel.com>
Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960
Mobile 0421-601 665


{Original Message removed}

2002\11\29@002718 by Chris Hunter

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H-P (now called "Agilent") make some really good "linear" opto-couplers.
These have an LED and TWO photodiodes in the package - you use the second
photodiode to provide linearising feedback in your drive circuit.  HCNR 200
& 201 are the devices you want, and the Agilent website has some goos app
notes which should show you how it's done.

Chris

{Original Message removed}

2002\11\29@080024 by Roman Black

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Peter Homann wrote:
>
> Hi,
>
> I'm planning to generate a 0-10V analog voltage using the PIC PWM, RC
> filter, and op-amp.
>
> The question is how do I isolate the output voltage. The voltage is to drive
> a 90V DC motor controller where the controller ground is live.


The smart solution is to isolate a digital
signal, not an analogue one. Get the PIC to
output a digital PWM, through a cheap opto-
coupler, and then filter to analogue with an
RC filter at the receiving end. :o)
-Roman

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2002\11\29@083217 by Michael Rigby-Jones

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{Quote hidden}

Note that most cheap opto-couplers are horribly slow.  Some devices I used
were hard pushed to get 10KHz through.

Mike

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2002\11\29@095547 by Mike Harrison

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Another solution might be to put a second, 8-pin PWM generating PIC on
the isolated end, with  slow isolated digital data through the opto.  On Fri, 29 Nov 2002 13:30:29 -0000, you wrote:

>> {Original Message removed}

2002\11\29@165746 by Olin Lathrop

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> I'm planning to generate a 0-10V analog voltage using the PIC PWM, RC
> filter, and op-amp.
>
> The question is how do I isolate the output voltage. The voltage is to
drive
> a 90V DC motor controller where the controller ground is live.
>
> One solution is to opto-isolate the inputs to the PIC and have the whole
> circuit live. I would have to power the PIC circuit via a 12V zener and
> resistor.
>
> The other option is to isolate the 10V signal via a transformer. Does
anyone
> have experience with this or other alternatives?

Why not use an opto-isolator on the PWM output signal from the PIC, then use
it to generate the analog voltage on the other side of the isolator?


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