piglet wrote...> >On 21/08/2019 9:34 am, Winfield Hill wrote: >> mook Jonhon wrote... >>> >>> 2) flyback to do most of the boost with a >>> doubler or tripler on the output. This >>> should keep the turns ratio reasonable. >> >> My flyback approach, previously detailed here >> on s.e.d., is different. Three flyback stages, >> each with its own MOSFET, all running from one >> controller and gate driver. The DC input-V of >> each stage is the previous stage's DC output. >> Starting with say 12V, you need a 167x stepup. >> Three 5.5x stages gets you to 2kV, and that's >> a pretty mild step-up ratio. 66V, 363V, 2kV. >> Stage currents and inductor values scale, since >> they all run with the same time parameters. >> >> Three feedback taps, each with a diode to the >> controller's FB pin. The highest one controls, >> to prevent any one stage from going excessively >> over its voltage limit, but the last stage gets >> the controlling vote. Very simple. Except for >> HV winding technique of the 3rd inductor. :-) > > But surely that triple cascaded flyback topology you > suggest would need a MOSFET with 2000V Vds rating?Details, details ... The HV MOSFET table in the x-Chapters goes up to 4kV. But they're expensive. The idea makes more sense up to 1.2 or 1.5kV. -- Thanks, - Win
48V to 2000V DC-DC smallest design
Started by ●August 20, 2019
Reply by ●August 21, 20192019-08-21
Reply by ●August 21, 20192019-08-21
On Wednesday, August 21, 2019 at 9:39:01 PM UTC+10, mook Jonhon wrote:> Tim Williams wrote: > > > How small is small? > > > > I made this without any particular care of size, > > https://www.seventransistorlabs.com/Images/HVPower2.jpg > > https://www.seventransistorlabs.com/Images/HVPower.jpg > > (What, a legible, hand drawn schematic? On SED? :^) ) > > > > Easy enough to fix up the DC supply side for efficiency (buck reg), > > fixed output, and drop the sense amp that's not needed. > > > > The chopper is kinda here-nor-there, but I do recommend a resonant > > type in any case as the secondary capacitance is unavoidable, and the > > Baxandall oscillator is fairly foolproof as oscillators go. > > > > Also, that was 12V input, but 48 isn't any trouble with appropriate > > changes. > > > > It seems there aren't many resonant controllers for smaller > > applications (like DC-DC modules), so you may have to make a discrete > > or digital controller if you want to go that route more formally. > > > > Probably a CCFL transformer would do, no need for custom transformers > > surprisingly enough. > > > > If you need it small as balls*, you can stick CSP package GaN > > transistors to the backside of a CCFL transformer, use a QFN or BGA > > controller (which again, might end up sorta custom, an FPGA or > > something), a few ceramic caps, probably a 4 or at most 6 layer > > board, and be done. > > > > *Erm, huh... literally about right, I think. You'd take up the other > > ball for the reservoir cap. And some insulation which might just > > wrap around the whole thing like a scrotum. I'll, uh, stop now. > > > > If that's too extreme, any combination of Si components and leaded or > > no-lead parts will do, requiring only somewhat more board area. > > > > Tim > > > Thanks Tim, > > I see you used a royer (push pull) with a voltage doubler on the back > side. > > by small I need something to fit in a 1" v 2" board with the tallest > components about 1/4" above or below the board. It could be 1/2" tall > as the board sits on 1/4" standoffs. think pot core bolted to teh > chassis on one end of the board. maybe some wiggle room to 2.5" in > length. > > I will need to run at highish frequencies (300+Khz) to get the > magnetics down but the continuous power levels will be low.Step-up transformers with lots of turns have lots of stray capacitance. Doublers and triplers and Cockroft-Walton stacks let you get away with lower turns ratios, fewer turns and lower secondary inductance, but 300kHz might be a bit hopeful. Getting something to fit on a 1" by 2" board (25mm by 50mm) and under half an inch (12mm) in height may be tricky too. Using printed windings in the transformer and inductor might help the height, but getting a much of a turns ratio might present problems. Entertaining problem. Have fun. With a Baxandall class-D oscillator - it may look like a Royer, but Peter Baxandall seems to have invented it to generate photomultiplier drive voltages and it's better than a Royer for that job - there's a pi/2 step up built in, so with a 45V rail you get 141V over the primary - 70.7V across the centre-tap at peak - so you'd only need a 15:1 turn ratio from primary to secondary to get to 2kV without a doubler.> what you are suggesting is where I was going. Just making sure therewas not trick or "old magic" that I was not aware of to simply make high votlage from low. :) Baxandall's Class-D oscillator is old magic. It goes back to 1959. Jim Williams used it - much later - for his back-light driver (Linear Technology application notes AN45, AN49, AN51, AN55, AN61, AN65). It has been suggested that he got the circuit from the UK without the link to the Baxandall paper http://sophia-elektronica.com/0344_001_Baxandal.pdf which isn't all that easy to get hold of (which is why I put my copy on my website a few years ago). -- Bill Sloman, Sydney
Reply by ●August 21, 20192019-08-21
Bill Sloman wrote...> mook Jonhon wrote: >> Tim Williams wrote: >>> >>> I made this without any particular care of size, >>> https://www.seventransistorlabs.com/Images/HVPower2.jpg >>> https://www.seventransistorlabs.com/Images/HVPower.jpgPush-pull osc. IMHO, way too high xfmr step-up ratio.>> I see you used a royer (push pull) with a voltage >> doubler on the back side.> Step-up transformers with lots of turns have lots of > stray capacitance. [ snip ] > > With a Baxandall class-D oscillator - it may look like a > Royer, but Peter Baxandall seems to have invented it ...A transformer with a push-pull primary driver is the best way to get bipolarity output currents, needed for optimum use of the Cockcroft-Walton diode step-up circuit. With say six stages of that, you can keep your transformer output voltages under 350V, greatly simplifying matters. Get the push pull from a center-tapped transformer, with several different possible driving schemes, or better (more efficient, smaller xfmr), drive a single primary with a half-bridge or full bridge. Available in ICs, at low power levels, with no external MOSFETs. -- Thanks, - Win
Reply by ●August 21, 20192019-08-21
On 21 Aug 2019 08:28:17 -0700, Winfield Hill <winfieldhill@yahoo.com> wrote:>Bill Sloman wrote... >> mook Jonhon wrote: >>> Tim Williams wrote: >>>> >>>> I made this without any particular care of size, >>>> https://www.seventransistorlabs.com/Images/HVPower2.jpg >>>> https://www.seventransistorlabs.com/Images/HVPower.jpg > > Push-pull osc. IMHO, way too high xfmr step-up ratio. > >>> I see you used a royer (push pull) with a voltage >>> doubler on the back side. > >> Step-up transformers with lots of turns have lots of >> stray capacitance. [ snip ] >> >> With a Baxandall class-D oscillator - it may look like a >> Royer, but Peter Baxandall seems to have invented it ... > > A transformer with a push-pull primary driver is the best > way to get bipolarity output currents, needed for optimum > use of the Cockcroft-Walton diode step-up circuit. With > say six stages of that, you can keep your transformer > output voltages under 350V, greatly simplifying matters. > > Get the push pull from a center-tapped transformer, > with several different possible driving schemes, or > better (more efficient, smaller xfmr), drive a single > primary with a half-bridge or full bridge. Available > in ICs, at low power levels, with no external MOSFETs.The flyback C-W circuit that I posted is simple and works fine. The C-W stack just needs p-p voltage of most any sort. https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1 That can deliver 8 watts at 1400 volts, so I had to heat sink the fet and the transformer with copper pours. That DRQ127 is being abused at that power. The problem with board size is not the parts, it's keeping the HV clearances. Conformal coating can help there.
Reply by ●August 21, 20192019-08-21
<jlarkin@highlandsniptechnology.com> wrote in message news:hbpqlelas5jo4e929g3lemri8k9njthf8d@4ax.com...> The flyback C-W circuit that I posted is simple and works fine. The > C-W stack just needs p-p voltage of most any sort.https://i.imgur.com/mbrcBLU.jpg If it's got a CW hanging off it, it ain't flyback. It may be peaky, but it ain't flyback. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Reply by ●August 21, 20192019-08-21
"mook Jonhon" <mook@mook.net> wrote in message news:k3a7F.5747$452.4002@fx02.iad...> I see you used a royer (push pull) with a voltage doubler on the back > side.NOT Royer -- the transformer is not saturating. Commutation is resonant, albeit badly so, because the leakage of the transformer wasn't very high. So it ran poorly under heavy load. But that's easily fixed with the right style transformer. And under nominal load, it ran around 65kHz with nicely rounded edges.> by small I need something to fit in a 1" v 2" board with the tallest > components about 1/4" above or below the board. It could be 1/2" tall > as the board sits on 1/4" standoffs. think pot core bolted to teh > chassis on one end of the board. maybe some wiggle room to 2.5" in > length.Yeah, that sounds about like what I described.> what you are suggesting is where I was going. Just making sure there > was not trick or "old magic" that I was not aware of to simply make > high votlage from low. :)I suppose the only "old magic" that applies is the Tesla coil, which is a pulsed power application. If you have adequate leakage in the transformer, you can drive it with a bridge for some number of cycles, and in that time the output voltage (and input current!) will ramp up and up and up, eventually flattening out as losses balance the input power (whether core loss, arcover, or rectifiers turning it into DC). The available output peak current is high, so the duty cycle is low. But I don't think this saves you anything, and you can already get a cored transformer of adequate rating, so you don't need to pound on an air-cored transformer to get it going this way. You'd end up taking more space not just for the coil but also the driver, because peak currents and energy storage (the input ripple would be a bitch :) ). The hysteretic approach to regulating output voltage may still be relevant. Baxandall (and Royer) oscillators work over a surprisingly wide supply voltage range, but they do eventually flounder at low voltages, and a hysteretic control, starting and stopping the oscillator, may be more efficient. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Reply by ●August 21, 20192019-08-21
On Wed, 21 Aug 2019 12:14:48 -0500, "Tim Williams" <tiwill@seventransistorlabs.com> wrote:><jlarkin@highlandsniptechnology.com> wrote in message >news:hbpqlelas5jo4e929g3lemri8k9njthf8d@4ax.com... >> The flyback C-W circuit that I posted is simple and works fine. The >> C-W stack just needs p-p voltage of most any sort. > >https://i.imgur.com/mbrcBLU.jpg >If it's got a CW hanging off it, it ain't flyback. It may be peaky, but it >ain't flyback. > >TimIt doesn't care what you call it. It works great.
Reply by ●August 21, 20192019-08-21
jlarkin@highlandsniptechnology.com wrote...> > Winfield Hill wrote: > >> A transformer with a push-pull primary driver is the best >> way to get bipolarity output currents, needed for optimum >> use of the Cockcroft-Walton diode step-up circuit. ... > > The flyback C-W circuit that I posted is simple and works > fine. The C-W stack just needs p-p voltage of most any sort.Yes, I know it works, and I puzzled over its asymmetry at the time. A flyback is very strong in one direction, but rather weak in the other. And your coupled inductor was another confounding factor, with its high capacitance.>https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1 > > That can deliver 8 watts at 1400 volts, so I had to heat > sink the fet and the transformer with copper pours. That > DRQ127 is being abused at that power.mook's power requirement is pretty low.> The problem with board size is not the parts, it's keeping > the HV clearances. Conformal coating can help there.-- Thanks, - Win
Reply by ●August 21, 20192019-08-21
On 21 Aug 2019 10:55:02 -0700, Winfield Hill <winfieldhill@yahoo.com> wrote:>jlarkin@highlandsniptechnology.com wrote... >> >> Winfield Hill wrote: >> >>> A transformer with a push-pull primary driver is the best >>> way to get bipolarity output currents, needed for optimum >>> use of the Cockcroft-Walton diode step-up circuit. ... >> >> The flyback C-W circuit that I posted is simple and works >> fine. The C-W stack just needs p-p voltage of most any sort. > > Yes, I know it works, and I puzzled over its asymmetry > at the time. A flyback is very strong in one direction, > but rather weak in the other. And your coupled inductor > was another confounding factor, with its high capacitance. > >>https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1 >> >> That can deliver 8 watts at 1400 volts, so I had to heat >> sink the fet and the transformer with copper pours. That >> DRQ127 is being abused at that power. > > mook's power requirement is pretty low.The mosfet source resistor sets the peak inductor current, hence the max power output and inductor stress. That tiny LTC chip is great and seems to always work. At low power, a smaller fet would be better... less drain capacitance to charge up. As you note, boost ratio is usually capacitance limited. It might be Spiced, or breadboarded, to optimize for lower power. I did both in my applications. There may be an optimum way to connect the 4 wires of the dual inductor autotransformer.
Reply by ●August 22, 20192019-08-22
On Thursday, August 22, 2019 at 1:49:45 AM UTC+10, jla...@highlandsniptechnology.com wrote:> On 21 Aug 2019 08:28:17 -0700, Winfield Hill <winfieldhill@yahoo.com> > wrote: > > >Bill Sloman wrote... > >> mook Jonhon wrote: > >>> Tim Williams wrote: > >>>> > >>>> I made this without any particular care of size, > >>>> https://www.seventransistorlabs.com/Images/HVPower2.jpg > >>>> https://www.seventransistorlabs.com/Images/HVPower.jpg > > > > Push-pull osc. IMHO, way too high xfmr step-up ratio. > > > >>> I see you used a royer (push pull) with a voltage > >>> doubler on the back side. > > > >> Step-up transformers with lots of turns have lots of > >> stray capacitance. [ snip ] > >> > >> With a Baxandall class-D oscillator - it may look like a > >> Royer, but Peter Baxandall seems to have invented it ... > > > > A transformer with a push-pull primary driver is the best > > way to get bipolarity output currents, needed for optimum > > use of the Cockcroft-Walton diode step-up circuit. With > > say six stages of that, you can keep your transformer > > output voltages under 350V, greatly simplifying matters. > > > > Get the push pull from a center-tapped transformer, > > with several different possible driving schemes, or > > better (more efficient, smaller xfmr), drive a single > > primary with a half-bridge or full bridge. Available > > in ICs, at low power levels, with no external MOSFETs. > > The flyback C-W circuit that I posted is simple and works fine. The > C-W stack just needs p-p voltage of most any sort. > > https://www.dropbox.com/s/r6o5krfl5p86cp5/T840_A.JPG?raw=1 > > That can deliver 8 watts at 1400 volts, so I had to heat sink the fet > and the transformer with copper pours. That DRQ127 is being abused at > that power. > > The problem with board size is not the parts, it's keeping the HV > clearances. Conformal coating can help there.The charm of the Baxandall class-D oscillator - as spelled out by Jim Williams, even if he didn't cal it that in Linear Technology's application notes AN45, AN49, AN51, AN55, AN61, AN65 - is that it can be 95% efficient, which can mean very little waste heat to be dissipated. -- Bill Sloman, Sydney
