Post by thread:[EE]: Generating an isolated 0-10Vdc voltage

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 spam_OUTPeter.HomannTakeThisOuTadacel.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 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> 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 -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

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.HomannKILLspam@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}

Try a capacitor dropper, rather than the resistor to feed your zener - you'll get less heat. Chris ----- Original Message ----- From: "Peter Homann" <peter.homannKILLspamADACEL.COM> To: <.....PICLISTKILLspam.....MITVMA.MIT.EDU> Sent: Friday, November 29, 2002 1:07 AM Subject: Re: [EE]: Generating an isolated 0-10Vdc voltage {Quote hidden}> 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 > EraseMEPeter.Homannspam_OUTTakeThisOuTadacel.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}

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.Homannspam_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}

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}

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 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

{Quote hidden}> -----Original Message----- > From: Roman Black [SMTP:@spam@fastvidKILLspamEZY.NET.AU] > Sent: Friday, November 29, 2002 12:54 PM > To: KILLspamPICLISTKILLspammitvma.mit.edu > Subject: Re: [EE]: Generating an isolated 0-10Vdc voltage > > 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 > Note that most cheap opto-couplers are horribly slow. Some devices I used were hard pushed to get 10KHz through. Mike -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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}

> 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? ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics