Forums

Isolated high voltage opamp

Started by bitrex May 24, 2015
On Mon, 25 May 2015 10:09:27 -0400 (EDT), bitrex
<bitrex@de.lete.earthlink.net> wrote:

>John S <Sophi.2@invalid.org> Wrote in message: >> On 5/24/2015 4:08 PM, John Larkin wrote: >>> On Sun, 24 May 2015 15:36:43 -0400 (EDT), bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> >>>> So I have a need for an analog isolation amplifier thing into a HV >>>> section at low audio frequencies. I remembered the "HV opamp" >>>> thing that John Larkin posted a while back and that seems to work >>>> well, but I'd like to isolate the feedback via pwming it and >>>> sending it back across the barrier via an optocoupler and >>>> integrating. I dont really want to chop it first and have more >>>> LV electronics on the HV side than necessary. >>>> >>>> Instead of having to pick a resistor divider for the largest >>>> possible output signal and lose resolution on the PWM I thought >>>> I'd bootstrap the PWM IC from the output like so: >>>> >>>> http://pastebin.com/1Ud9R9nM >>>> >>>> The components are all just representative and probably not what >>>> I'd actually use. It seems like this test circuit should work >>>> (the full loop hasn't been closed) but it doesn't appear to sim >>>> properly. >>>> >>>> Any ideas? >>> >>> >>> I tweaked the basic HV opamp circuit a little... >> >> Looks good but I guess we need to know how much isolation he needs. >> Yours is 1Meg out-to-in, yes? Also, the 1Meg has a voltage limit as >> discussed in another thread. >> >> Have I overlooked something? >> >> > >At the moment the +150 -150 volts is sufficient, but I was also > interested in developing a topology that would work for > significantly higher voltages...like a thousand or more plus to > minus. I don't thinka resistor from output to input would be > appropriate in that case. Hence the PWM idea.
Watch for the Apex PA99, coming soon... 2500V total supply... I begin behavioral modeling it the first week of June. ...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.
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. -- Thanks, - Win
On Mon, 25 May 2015 08:14:15 -0500, John S <Sophi.2@invalid.org>
wrote:

>On 5/24/2015 4:08 PM, John Larkin wrote: >> On Sun, 24 May 2015 15:36:43 -0400 (EDT), bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> >>> So I have a need for an analog isolation amplifier thing into a HV >>> section at low audio frequencies. I remembered the "HV opamp" >>> thing that John Larkin posted a while back and that seems to work >>> well, but I'd like to isolate the feedback via pwming it and >>> sending it back across the barrier via an optocoupler and >>> integrating. I dont really want to chop it first and have more >>> LV electronics on the HV side than necessary. >>> >>> Instead of having to pick a resistor divider for the largest >>> possible output signal and lose resolution on the PWM I thought >>> I'd bootstrap the PWM IC from the output like so: >>> >>> http://pastebin.com/1Ud9R9nM >>> >>> The components are all just representative and probably not what >>> I'd actually use. It seems like this test circuit should work >>> (the full loop hasn't been closed) but it doesn't appear to sim >>> properly. >>> >>> Any ideas? >> >> >> I tweaked the basic HV opamp circuit a little... > >Looks good but I guess we need to know how much isolation he needs. >Yours is 1Meg out-to-in, yes? Also, the 1Meg has a voltage limit as >discussed in another thread. > >Have I overlooked something?
The ones we drew aren't isolated at all; the power supplies are all grounded. I guess the idea of the deleted PWM box is to measure some voltage and opto-couple it back to the grounded side, which would allow shuffling grounds to give full isolation. I'm not sure.
On Mon, 25 May 2015 10:09:27 -0400 (EDT), bitrex
<bitrex@de.lete.earthlink.net> wrote:

>John S <Sophi.2@invalid.org> Wrote in message: >> On 5/24/2015 4:08 PM, John Larkin wrote: >>> On Sun, 24 May 2015 15:36:43 -0400 (EDT), bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> >>>> So I have a need for an analog isolation amplifier thing into a HV >>>> section at low audio frequencies. I remembered the "HV opamp" >>>> thing that John Larkin posted a while back and that seems to work >>>> well, but I'd like to isolate the feedback via pwming it and >>>> sending it back across the barrier via an optocoupler and >>>> integrating. I dont really want to chop it first and have more >>>> LV electronics on the HV side than necessary. >>>> >>>> Instead of having to pick a resistor divider for the largest >>>> possible output signal and lose resolution on the PWM I thought >>>> I'd bootstrap the PWM IC from the output like so: >>>> >>>> http://pastebin.com/1Ud9R9nM >>>> >>>> The components are all just representative and probably not what >>>> I'd actually use. It seems like this test circuit should work >>>> (the full loop hasn't been closed) but it doesn't appear to sim >>>> properly. >>>> >>>> Any ideas? >>> >>> >>> I tweaked the basic HV opamp circuit a little... >> >> Looks good but I guess we need to know how much isolation he needs. >> Yours is 1Meg out-to-in, yes? Also, the 1Meg has a voltage limit as >> discussed in another thread. >> >> Have I overlooked something? >> >> > >At the moment the +150 -150 volts is sufficient, but I was also > interested in developing a topology that would work for > significantly higher voltages...like a thousand or more plus to > minus. I don't thinka resistor from output to input would be > appropriate in that case. Hence the PWM idea.
Unless you plan to float the +-HV supplies, to get true isolation, a feedback sense resistor will work fine. 100 Meg, 1 G, something like that. Powering a PWM circuit from kilovolt supplies will be inefficient. To push my circuit past the voltage rating of the MOC8204s, you can cascode better, low voltage optocouplers into depletion fets. Or use photovoltaic optocouplers into conventional high voltage mosfets. Easy but slow.
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.
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 -- | 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.
On Mon, 25 May 2015 08:58:48 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>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
Since Spice usually ignores breakdown voltages, you may as well simulate with some part that's in the standard library.
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> Wrote in
 message:
> On Mon, 25 May 2015 08:14:15 -0500, John S <Sophi.2@invalid.org> > wrote: > >>On 5/24/2015 4:08 PM, John Larkin wrote: >>> On Sun, 24 May 2015 15:36:43 -0400 (EDT), bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> >>>> So I have a need for an analog isolation amplifier thing into a HV >>>> section at low audio frequencies. I remembered the "HV opamp" >>>> thing that John Larkin posted a while back and that seems to work >>>> well, but I'd like to isolate the feedback via pwming it and >>>> sending it back across the barrier via an optocoupler and >>>> integrating. I dont really want to chop it first and have more >>>> LV electronics on the HV side than necessary. >>>> >>>> Instead of having to pick a resistor divider for the largest >>>> possible output signal and lose resolution on the PWM I thought >>>> I'd bootstrap the PWM IC from the output like so: >>>> >>>> http://pastebin.com/1Ud9R9nM >>>> >>>> The components are all just representative and probably not what >>>> I'd actually use. It seems like this test circuit should work >>>> (the full loop hasn't been closed) but it doesn't appear to sim >>>> properly. >>>> >>>> Any ideas? >>> >>> >>> I tweaked the basic HV opamp circuit a little... >> >>Looks good but I guess we need to know how much isolation he needs. >>Yours is 1Meg out-to-in, yes? Also, the 1Meg has a voltage limit as >>discussed in another thread. >> >>Have I overlooked something? > > The ones we drew aren't isolated at all; the power supplies are all > grounded. > > I guess the idea of the deleted PWM box is to measure some voltage and > opto-couple it back to the grounded side, which would allow shuffling > grounds to give full isolation. I'm not sure. >
Correct -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
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. -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
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 -- | 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.