Forums

Isolated high voltage opamp

Started by bitrex May 24, 2015
Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com>
 Wrote in message:
> On Mon, 25 May 2015 16:47:00 -0400 (EDT), bitrex > <bitrex@de.lete.earthlink.net> wrote: > >>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> >> Wrote in message: >>> On Mon, 25 May 2015 08:38:31 -0700, John Larkin >>> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On 25 May 2015 07:52:50 -0700, Winfield Hill >>>><hill@rowland.harvard.edu> wrote: >>>> >>>>>John Larkin wrote... >>>>>> >>>>>> bitrex wrote: >>>>>>> >>>>>>> So I have a need for an analog isolation amplifier >>>>>>> thing into a HV section at low audio frequencies. ... >>>>>> >>>>>> I tweaked the basic HV opamp circuit a little... >>>>>> >>>>>> Version 4 [snip] >>>>> >>>>> Fairchild's MOC207 is rated at 70V, whereas their >>>>> MOC8204 is rated at 400V. The CTR is much lower. >>>>> Watch out for the class-A current * 400 volts. >>>> >>>>That's my original circuit, from 2005 I think. >>>> >>>>https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPG >>>> >>>>I used it to bias the collection electrodes in a 2D delay-line >>>>detector, behind a microchannel plate. Didn't make any money, but it >>>>was fun. >>>> >>> >>> That ought to work for bitrex. >>> >>> ...Jim Thompson >>> -- >> >>Yes, that should. I was experimenting with also isolating the >> feedback loop with PWM and an optocoupler for total galvanic >> isolation, but cannot seem to pull it off. > > What's the frequency of your signal? If it's essentially DC, PWM > should be relatively easy... ramp and dump? > > ...Jim Thompson > --
No more than about 5khz. The PWM chip takes an input voltage between 0 and 1 volt, so the idea was to float the PWM IC so its rails ride up and down on top of the output voltage and divide the modulation input down from the output, referred to the floating "ground" so as not to lose resolution. But the LT chip doesn't seem to cooperate with the idea. -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
On Mon, 25 May 2015 17:55:30 -0400 (EDT), bitrex
<bitrex@de.lete.earthlink.net> wrote:

>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> > Wrote in message: >> On Mon, 25 May 2015 16:47:00 -0400 (EDT), bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> >>> Wrote in message:
[snip]
>>>> That ought to work for bitrex. >>>> >>>> ...Jim Thompson >>>> -- >>> >>>Yes, that should. I was experimenting with also isolating the >>> feedback loop with PWM and an optocoupler for total galvanic >>> isolation, but cannot seem to pull it off. >> >> What's the frequency of your signal? If it's essentially DC, PWM >> should be relatively easy... ramp and dump? >> >> ...Jim Thompson >> -- > >No more than about 5khz. The PWM chip takes an input voltage > between 0 and 1 volt, so the idea was to float the PWM IC so its > rails ride up and down on top of the output voltage and divide > the modulation input down from the output, referred to the > floating "ground" so as not to lose resolution. > >But the LT chip doesn't seem to cooperate with the idea.
I'm not following what you mean. What's the definition of _common_ on the load side ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.