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From: Tim Williams on 12 Jul 2010 13:17 "Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:i1f10m$1b2$1(a)news.albasani.net... > But I cannot follow you there, sure it works, but you lose power in that snubber? > I did the same for a 300 MHz transistor scope, had some more turns, > but used the above tuned circuit. > But I went up from 12V DC to a couple of kV IIRC. Well, I'm making 2kV here, and at my line voltage, it was making 3kV before I installed the regulator: http://myweb.msoe.edu/williamstm/Images/Tubescope_Supply2.png 3 > "couple", so it's in the ballpark. If you meant directly, not with a doubler, then that'd be a bit more, sure. > No power losses in snubbers, no hot components! I have learned it is a Good Thing to be paranoid about the voltage specs on things. I put peak snubbers on everything. Probably not necessary in this case, but better safe than sorry. It only burns a fraction of a watt so it's not a big deal. > Also have a look at the old TV CRT H output stages, boost diode > configurations. They did that by adding extra windings. I don't mind winding, but if it's just for a snubber, what the hell, I'll just leak it off in a resistor. When inductance is high enough, the loss is small. I recently took apart an iMac power supply that had a UC3842 based power supply: transformer, FET, clamp diode, the works. But it also had a ferrite cored filter inductor. I don't know why, but they went with a half wave forward converter, instead of the 3842's textbook flyback circuit. It was only a 5W resistor, so it's not like it was costing much efficiency. Hell of a lot better than destroying your 800V MOSFET, too. > Anytime I see a 'snubber' my alarm goes off :-) > Here a nice very old HV supply with build in rectifier: > ftp://panteltje.com/pub/HeNe_laser_hv_supply_img_2070.jpg > side view: > ftp://panteltje.com/pub/HeNe_laser_HV_supply_sideview_img_2069.jpg > > This thing produces great sparks, it is a 555 timer switching a TIP140 > power transistor. Not bad, though mine makes greater sparks :) http://www.youtube.com/watch?v=NEQCy44AuJk > The grey thing holds the HV transformer and HV diode. > Runs on 6 or 12 V (do not remember), bought it in the eighties for a helium > neon laser > I had. > Lost the diagram... > But you will note the absence of any 'snubbers', in fact nothing gets hot. > Snubbers indicates low efficiency :-) Snubbers are OK to skip where there's a lot of capacitance. This effectively makes a "lossless" snubber. The downside is, it gets very frequency sensitive (think induction heater), or draws lots of reactive current (bad for caps), or something like that. For instance, your transistor sucks a big startup surge. It's only a microsecond, so it doesn't matter, but if it were doing it every cycle, in hard switching instead of ZVS, it would be dead. So it's not a generally applicable approach. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jan Panteltje on 12 Jul 2010 13:44 On a sunny day (Mon, 12 Jul 2010 12:17:38 -0500) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <X6I_n.11338$Hw.1854(a)newsfe10.iad>: >"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message = >news:i1f10m$1b2$1(a)news.albasani.net... >> But I cannot follow you there, sure it works, but you lose power in = >that snubber? >> I did the same for a 300 MHz transistor scope, had some more turns, >> but used the above tuned circuit. >> But I went up from 12V DC to a couple of kV IIRC. > >Well, I'm making 2kV here, and at my line voltage, it was making 3kV = >before I installed the regulator: >http://myweb.msoe.edu/williamstm/Images/Tubescope_Supply2.png >3 > "couple", so it's in the ballpark. If you meant directly, not with = >a doubler, then that'd be a bit more, sure. > >> No power losses in snubbers, no hot components! > >I have learned it is a Good Thing to be paranoid about the voltage specs = >on things. I put peak snubbers on everything. Probably not necessary = >in this case, but better safe than sorry. It only burns a fraction of a = >watt so it's not a big deal. OK, I was getting the wrong impression perhaps because you marked it as '1 W'. As for the high voltage, I had (or have?) a lot of those TV H output transistors, BU208 and things like that. They are great, 700V Vce or more. >I recently took apart an iMac power supply that had a UC3842 based power = >supply: transformer, FET, clamp diode, the works. But it also had a = >ferrite cored filter inductor. I don't know why, but they went with a = >half wave forward converter, instead of the 3842's textbook flyback = >circuit. > >It was only a 5W resistor, so it's not like it was costing much = >efficiency. Hell of a lot better than destroying your 800V MOSFET, too. >> Anytime I see a 'snubber' my alarm goes off :-) >> Here a nice very old HV supply with build in rectifier: >> ftp://panteltje.com/pub/HeNe_laser_hv_supply_img_2070.jpg >> side view: >> ftp://panteltje.com/pub/HeNe_laser_HV_supply_sideview_img_2069.jpg >> >> This thing produces great sparks, it is a 555 timer switching a TIP140 >> power transistor. > >Not bad, though mine makes greater sparks :) >http://www.youtube.com/watch?v=NEQCy44AuJk Cool. I once was repairing a color set, and forgot to put the HV cap back on the tube, it was hanging of the workbench net to my leg. I got zapped with 25 kV. Was not so bad, quick to power down. >> The grey thing holds the HV transformer and HV diode. >> Runs on 6 or 12 V (do not remember), bought it in the eighties for a = >helium >> neon laser >> I had. >> Lost the diagram... >> But you will note the absence of any 'snubbers', in fact nothing gets = >hot. >> Snubbers indicates low efficiency :-) > >Snubbers are OK to skip where there's a lot of capacitance. This = >effectively makes a "lossless" snubber. The downside is, it gets very = >frequency sensitive (think induction heater), or draws lots of reactive = >current (bad for caps), or something like that. But much better to tune the thing? Square waves radiate a lot...
From: Tim Williams on 12 Jul 2010 14:02 "Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:i1fkaj$9l$1(a)news.albasani.net... > OK, I was getting the wrong impression perhaps because you marked it as > '1 W'. > As for the high voltage, I had (or have?) a lot of those TV H output > transistors, BU208 and things like that. > They are great, 700V Vce or more. Oddly, I recently tried making an absurdly high ratio boost converter with a 2SC5404 (same old 10A 1.5kVcbo thing). It was avalanching at only 300V. I think this was because I wasn't driving the base negative, only "off" (shunted to GND with a power MOSFET). I replaced it with an 800V MOSFET, which dutifully went right up to 820V peak. Not a bad ratio for a 16V supply. >>Snubbers are OK to skip where there's a lot of capacitance. This = >>effectively makes a "lossless" snubber. The downside is, it gets very = >>frequency sensitive (think induction heater), or draws lots of reactive = >>current (bad for caps), or something like that. > > But much better to tune the thing? > Square waves radiate a lot... Tune? BTW, you might want to check your newsreader's settings. In previous posts, you've mentioned an interest in the workings of Usenet so I'm guessing you'll be interested. Take the above quote for instance, it has been erroneously appended with equals signs. I'm guessing the encoding isn't set correctly. If it were, either the equals wouldn't be placed, or my newsreader would remove them appropriately. In other passages (like the second line of your first quote in this message), your random-length lines wrap at inopportune points, resulting in ugly paragraphs. I don't have a clue how my posts (quoted-printable encoding) appear to other newsreaders; in my own, they wrap to the window width, which is perfectly readable. AlwaysWrong seems to object as if they don't wrap at all; maybe he has to read them with a horizontal scroll bar. In his case, I consider that an advantage... but I wonder about others. I do know that some newsreaders (including OE) have trouble quoting "quoted-printable" (which seems rather ironic). The "> " marks don't get added automatically, which is annoying. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Devereux on 12 Jul 2010 14:31 "Tim Williams" <tmoranwms(a)charter.net> writes: [...] > I don't have a clue how my posts (quoted-printable encoding) appear to > other newsreaders; in my own, they wrap to the window width, which is > perfectly readable. AlwaysWrong seems to object as if they don't wrap > at all; maybe he has to read them with a horizontal scroll bar. In > his case, I consider that an advantage... but I wonder about others. I believe the usenet standard is to wrap lines (i.e. insert linefeeds) at ~60-70 characters (to allow for quoting on a 80 character screen I guess). It is also a convenient width to read, long lines are tiring. Mine warns me if I try to post ones much longer than this, so I wrapped yours (above). Your long lines are a bit awkward to read IMO, but nothing too obnoxious:) > I do know that some newsreaders (including OE) have trouble quoting > "quoted-printable" (which seems rather ironic). The "> " marks don't > get added automatically, which is annoying. > > Tim -- John Devereux
From: Tim Williams on 12 Jul 2010 18:28
"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:i1g15t$l60$1(a)news.albasani.net... > I really have not tried any HV MOSFETS other then BUZ44A (400V) many > years ago. Odd. A shame, I guess? 500 and 800V FETs are handy for around-the-world supplies, 500V for PFC and forward converters, and 800-1000V for flybacks. IGBTs are better than FETs above 300V, and are cheaper per amp, but good luck finding any inbetween 600V and 1200V, those seem to be the most popular voltages for some reason. They aren't all that popular for lower currents, where FETs still dominate AFAIK. They also seem to be more fragile, not tolerating excess voltage in forward or reverse (co-pack IGBTs, with diode, solve the reverse problem for the most part). It's kind of weird, they're rated for avalanche breakdown voltage (at a current of like 1mA), but I have never seen an energy rating on them (like FETs have). As far as I know, more than a few mA causes destruction for some reason. > OK, let me try to explain my way of thinking, maybe bit vague for some, > but it goes like this: > It is much easier to keep a pendulum going then moving it fast left to right > or forward backward, takes less energy. > I like resonant, way of least resistance. > As you have capacitance in the transformer windings plus lots of other places, > why not make use of it and tune things. Ah, but how much energy do you really burn in switching? In general I mean. And note that, in general, "tuning" (which I guess does refer to resonant or quasi-resonant snubbers, tuned circuits, that sort of thing) is not possible, and obviously enough it increases reactive current, which may be troublesome. A generalization can't be made, but it might be anywhere from the miniscule amount of q = C * deltaV or Phi = L * deltaI parasitics, to several times load current typical of LLC circuits and etc. The thing about tuning, and something you absolutely must remember: it doesn't *help* you. If it's there unavoidably, you should take advantage of it; but don't be under any illusion that adding reactive components will make a circuit work better. Two extremes make a great example. One, a high voltage generator with huge capacitive secondary, and the other, a forward converter with essentially resistive behavior. For the HV generator, you could drive it with a single transistor (as your laser supply does), with the disadvantages of: turn-on transient switches full capacitance = big current spike, frequency and duty cycle must be set to maintain class E operation, leakage inductance must be low enough (or primary capacitance high enough) to minimize overshoot at the primary (otherwise you need voltage peak snub), and the extra reactive current causes increased heating in the supply filter cap, some amount of current in the transistor and now-required damper diode, and additional heating in both the primary and secondary due to that capacitive reactance. Further advantage could be taken by driving the transformer with a [dynamic] current source, i.e., an inductor. This doesn't work very well in half wave, but it does work well in full wave, e.g. PP or full bridge. You get a Royer oscillator, where the voltage swings in sinusoidal humps, both transistors operate in ZVS, with no reactive current flowing through the supply (it's all squashed by the series inductor, which can be arbitrarily large), and the output is a fairly clean sine wave, limited only by Q and switching speed (during zero crossing, when both transistors are on simultaneously, a flat spot occurs). The basic point is, since you have capacitance, you might as well use it. This might involve canceling the reactance with inductors, or using a capacitor-friendly approach, like CC drive. Keep in mind that, by increasing absolute current and voltage, you are increasing losses, maybe not as much as an explicit snubber, but some nonetheless. The forward converter, on the other hand, works like this: the transistor turns on, current shoots up proportionally, then it turns off and current goes to zero. There is nothing to "swing" and start the cycle, nor anything to end it; timing is arbitrary. Whereas the mechanical analogy of a pendulum seems to be easier, this example is more like dragging a weighted block across the floor: voltage (velocity) doesn't go anywhere until you apply a certain amount of current (force, static coefficient of friction). When you apply that voltage in either direction, a proportional current (including direction) flows. It doesn't help you to apply reactive forces (vibration, hammer taps, etc.), because friction is friction (note: the dynamic coefficient of friction is always lower than static, but in this electronic analogy, they are equal). So either way, you have to apply the work, and yes it takes some effort to get up to that level of force/velocity, but you don't have anything to help you, and it's a completely lossy system anyway, so it won't even 'feel' right. You'll have to apply so much reactive energy that you'll definitely increase losses trying to reach an underdamped (feels-kinda-resonant) system. Now, this is all obvious to us, but it's amazing that it escapes the overunity types. They are quite fond of two things: rotating/oscillating machinery and circuitry, and anything that seems to operate on little enough power that it "feels" lossless to the hand. One silly example uses several miliwebers of seriously strong supermagnets, arranged without any pole pieces whatsoever, in a ring glued to a disc, such that the magnetic field on the periphery seems to ramp up, going around the disc. The result is, when another magnet is held near the disc, the magnets in the ring push away, and as the field ramps down, the ring is propelled. Obviously, it won't be propelled a whole revolution, because there's a step where the ramp begins again. The astute operator just happens to nudge his wrist at this moment, thus apparently making a "magnetic motor" that rotates without "any" energy input whatsoever; the magnets seem to push themselves around! I expect the two effects at work apparently convincing this operator of the energy arises from 1. the force being almost entirely radial (= force that does no work), except for an imperceptible tangential force (doing the actual work), and 2. because the amount of force required to spin a disc on a bearing is small, the energy input (that nudge of the wrist) is also small, perhaps being imperceptible as well, giving rise to the illusion that it happens of its own energy. And apparently Tesla himself was convinced of this fallacy. Reactive power is energy, not power. It is fundamentally impossible to accumulate energy in a resonant system -- it will always come to equilibrium for constant power input! Such belief has even been professed on this newsgroup from time to time -- Jim Thompson once spoke of an LC sinewave oscillator he constructed which required no "gain correction", like the classic HP Wein bridge oscillator has. This is of course another fallacy, since a true linear oscillator will grow without bound, but given a sufficiently high Q, a small constant-current nudge (of constant amplitude -- not a linear system!) to a parallel resonant tank will appear as linear (low distortion) as anything else. The same is true of a series resonant circuit and small constant voltage stimulus, but series resonant tanks are harder to implement on the small signal level; for a resonant voltage of 5V and Q = 100, you have to drive the thing with a perfect voltage source of only 50mV, whereas the parallel resonant, carrying 10mA reactive, can be tweaked with only 0.1mA. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |