On Sun, 11 Oct 2015 17:24:37 -0700 (PDT), Bill Sloman <bill.sloman@gmail.com> Gave us:>and I'd tend to pick one that was guaranteed to act as a > fuse by blowing to open circuit under overload.Absolutely a stupid statement. HV supplies are potted and non-serviceable and the thing has to survive numerous arcing events and keep on ticking after that licking. You really know absolutely nothing about this.
HV OpAmp
Started by ●October 11, 2015
Reply by ●October 11, 20152015-10-11
Reply by ●October 11, 20152015-10-11
On Sun, 11 Oct 2015 17:24:37 -0700 (PDT), Bill Sloman <bill.sloman@gmail.com> Gave us:>Carbon film and carbon composition resistors don't reliably stop that. >Yes they do. They damp the impulse created by the arc, which is exactly what their function in the circuit is. You really know absolutely nothing about HV supplies.
Reply by ●October 11, 20152015-10-11
On Monday, 12 October 2015 11:59:28 UTC+11, DecadentLinuxUserNumeroUno wrote:> On Sun, 11 Oct 2015 17:24:37 -0700 (PDT), Bill Sloman > <bill.sloman@gmail.com> Gave us: > > >Carbon film and carbon composition resistors don't reliably stop that. > > > Yes they do. They damp the impulse created by the arc, which is > exactly what their function in the circuit is. > > You really know absolutely nothing about HV supplies.You know absolutely nothing about negative temperature coefficient resistors. Once a hot channel is formed, it's resistance is too low to damp anything. -- Bill Sloman, Sydney
Reply by ●October 12, 20152015-10-12
On Sunday, October 11, 2015 at 9:35:59 AM UTC-7, Jim Thompson wrote:> HV OpAmp... > > <http://www.analog-innovations.com/SED/HV_OpAmp_2015-10-11.png>If you could get a HV PNP transistor to level-translate, it can be simplified further. For +/- 150V outputs, the pullup/pulldown NPNs have to take 300V, the PNP only takes 150V. Op amp output through limit resistor to PNP emitter, base grounded, and the collector drives the pulldown NPN base (suitable base-to-negative and emitter resistors on the HV NPN). Depending on the op amp, I'd consider allowing for a speedup capacitor across the high-value feedback resistor. It might be worthwhile shielding it,too; big resistances give me an itchy feeling
Reply by ●October 12, 20152015-10-12
On Mon, 12 Oct 2015 13:37:22 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Sunday, October 11, 2015 at 9:35:59 AM UTC-7, Jim Thompson wrote: >> HV OpAmp... >> >> <http://www.analog-innovations.com/SED/HV_OpAmp_2015-10-11.png> > >If you could get a HV PNP transistor to level-translate, it can be simplified further. >For +/- 150V outputs, the pullup/pulldown NPNs have to take 300V, >the PNP only takes 150V. > > Op amp output through limit resistor to PNP emitter, base grounded, >and the collector drives the pulldown NPN base (suitable base-to-negative and emitter >resistors on the HV NPN). > >Depending on the op amp, I'd consider allowing for a speedup capacitor across >the high-value feedback resistor. It might be worthwhile shielding it,too; >big resistances give me an itchy feelingThat circuit was just a demonstration that all you need is a low voltage opto-coupler with a cascode. Having now Spice-modeled Apex' MP118 (+/-100V) and PA99 (+/-1250V) OpAmps, IRL I'd use current mirrors and a more classic NPN/PNP complementary output stage... makes it easier to compensate. This one, by Larkin... <https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPG> simulates just fine, but would smoke in-real-life. Cascoding avoids the "suicide-bias" issue. A later Larkin post using depletion mode FET's looks feasible. ...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.
Reply by ●October 12, 20152015-10-12
On Mon, 12 Oct 2015 13:37:22 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Sunday, October 11, 2015 at 9:35:59 AM UTC-7, Jim Thompson wrote: >> HV OpAmp... >> >> <http://www.analog-innovations.com/SED/HV_OpAmp_2015-10-11.png> > >If you could get a HV PNP transistor to level-translate, it can be simplified further. >For +/- 150V outputs, the pullup/pulldown NPNs have to take 300V, >the PNP only takes 150V. > > Op amp output through limit resistor to PNP emitter, base grounded, >and the collector drives the pulldown NPN base (suitable base-to-negative and emitter >resistors on the HV NPN). > >Depending on the op amp, I'd consider allowing for a speedup capacitor across >the high-value feedback resistor. It might be worthwhile shielding it,too; >big resistances give me an itchy feelingYou can also get cutesy with opto-coupled current mirrors... <http://www.analog-innovations.com/SED/OptoCoupledCurrentMirrors_2015-10-12.png> You can get matched optocouplers, for example Vishay ILD615... I don't have a model, but you get the idea. Controlling the current gain is important to be thermal and AC stability. ...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.
Reply by ●October 12, 20152015-10-12
On Mon, 12 Oct 2015 14:59:39 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Mon, 12 Oct 2015 13:37:22 -0700 (PDT), whit3rd <whit3rd@gmail.com> >wrote: > >>On Sunday, October 11, 2015 at 9:35:59 AM UTC-7, Jim Thompson wrote: >>> HV OpAmp... >>> >>> <http://www.analog-innovations.com/SED/HV_OpAmp_2015-10-11.png> >> >>If you could get a HV PNP transistor to level-translate, it can be simplified further. >>For +/- 150V outputs, the pullup/pulldown NPNs have to take 300V, >>the PNP only takes 150V. >> >> Op amp output through limit resistor to PNP emitter, base grounded, >>and the collector drives the pulldown NPN base (suitable base-to-negative and emitter >>resistors on the HV NPN). >> >>Depending on the op amp, I'd consider allowing for a speedup capacitor across >>the high-value feedback resistor. It might be worthwhile shielding it,too; >>big resistances give me an itchy feeling > >That circuit was just a demonstration that all you need is a low >voltage opto-coupler with a cascode. > >Having now Spice-modeled Apex' MP118 (+/-100V) and PA99 (+/-1250V) >OpAmps, IRL I'd use current mirrors and a more classic NPN/PNP >complementary output stage... makes it easier to compensate.The Apex amps that I've looked at had horrendous quiescent power dissipations, especially using their recommended app circuits. I'm designing a HV driver right now, an Apex replacement, that has about 0.1% of their dissipation.> >This one, by Larkin... > ><https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPG> > >simulates just fine, but would smoke in-real-life. >Why? I've shipped products with this circuit, no problems. Yours would fry the resistors at higher voltages. R2 is dissipating 200 mW already. The opamp quiescent supply current sets the opto class-AB quiescent current. One can add a resistor across the opamp rails if you want more, which one probably doesn't here. The MOC should have b-e resistors at higher voltages. B-E resistors can actually move it into full class-B if you want. Or do that on the LED side. But I really like the perfect class AB current splitting that comes from putting the LEDs in the opamp rails.> >Cascoding avoids the "suicide-bias" issue.It works fine if you get the numbers right.> >A later Larkin post using depletion mode FET's looks feasible.I've shipped that, too. Supertex makes depletion fets up to 700 volts. Their new web site tries to keep that secret. At high voltages or currents, the PV thing with an enhancement mosfet works best. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 13, 20152015-10-13
On Sunday, 11 October 2015 17:35:59 UTC+1, Jim Thompson wrote:> HV OpAmp... > > <http://www.analog-innovations.com/SED/HV_OpAmp_2015-10-11.png> > > Can be built to arbitrary HV supplies, just change Q1 and Q2 to higher > voltage devices. > > ...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.When I saw this thread I thought, ah-ah Kilovolts. But, no. Anyway I thought I must add that I made an amplifier with an 18KV positive rail for driving a penetration phosphor CRT. Colour change with variation of the final HT, 8 to 16 KV. In the mid/late 60's I used a pair of experimental MOV triodes (valves/tubes) in direct-coupled class AB driven from a 741 (what's that)to perform the colour change. We had to modulate the deflection system in synchronism to maintain the picture size. It worked satisfactorily so we thought we had better get rid of the valves/tubes, because it was going to have to fly. For the "solid-state" version we ended up using a stack of TV line output transistors (BUY 69 rings a bell)in the output stage. Interesting times.
Reply by ●October 13, 20152015-10-13
On Tue, 13 Oct 2015 14:20:36 -0700 (PDT), grahamholloway@graham65.plus.com wrote:>On Sunday, 11 October 2015 17:35:59 UTC+1, Jim Thompson wrote: >> HV OpAmp... >> >> <http://www.analog-innovations.com/SED/HV_OpAmp_2015-10-11.png> >> >> Can be built to arbitrary HV supplies, just change Q1 and Q2 to higher >> voltage devices. >> >> ...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. > >When I saw this thread I thought, ah-ah Kilovolts. But, no. > >Anyway I thought I must add that I made an amplifier with an 18KV positive rail for driving a penetration phosphor CRT. Colour change with variation of the final HT, 8 to 16 KV. In the mid/late 60's I used a pair of experimental MOV triodes (valves/tubes) in direct-coupled class AB driven from a 741 (what's that)to perform the colour change. We had to modulate the deflection system in synchronism to maintain the picture size. It worked satisfactorily so we thought we had better get rid of the valves/tubes, because it was going to have to fly. For the "solid-state" version we ended up using a stack of TV line output transistors (BUY 69 rings a bell)in the output stage. Interesting times.I'd still seriously consider tubes if I had to make a 30 KV amplifier. A 1B3 is a nice slow amplifier if the input is the filament voltage. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 14, 20152015-10-14
On Tuesday, 13 October 2015 23:28:17 UTC+1, John Larkin wrote:> I'd still seriously consider tubes if I had to make a 30 KV amplifier. > > A 1B3 is a nice slow amplifier if the input is the filament voltage.Memory on this not what it should be, but I thought drawing max possible i from a filament shortened its life greatly. NT
