Piotr Wyderski wrote: Just a supplement: the interesting part is IMO discharging the caps through the flyback chokes. It makes the pulses at no additional energy cost (beyond what has already been transferred through the 100M resistors), so they are both signal and power at the same time. Unfortunately, the amount of energy stored in that 470p capacitor charged to 1V is so tiny that the autotransformer is not able to boost the voltage (merely ~150mV at the low V_IN end) to open Q3. This is a constant energy regime: if you add more turns to L3, the voltage reaches some saturation point and the reset pulses are getting longer instead, as L and C both go up. This saturation point is ~400mV, too low for an NPN to notice (assuming zero power detection; you can't afford a proper PNP long tailed pair). A 400mV EPAD would cut the mustard, but another solution is to double the amount of energy deposited to the core. Hence the dual-pumping idea utilising L1 and L4. With that it works even down to 1.1V V_IN. Balancing these available picojoules is sort of obscene. :) Best regards, Piotr
BJT behaviour at ridiculously low current levels
Started by ●May 11, 2022
Reply by ●May 25, 20222022-05-25
Reply by ●May 25, 20222022-05-25
jlarkin@highlandsniptechnology.com wrote:> On Tue, 24 May 2022 16:47:30 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> jlarkin@highlandsniptechnology.com wrote: >>> On Tue, 24 May 2022 10:08:29 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> John Larkin wrote: >>>>> On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whit3rd@gmail.com> >>>>> wrote: >>>>> >>>>>> On Monday, May 23, 2022 at 10:19:30 AM UTC-7, John Larkin wrote: >>>>>> >>>>>>> I want an LED blinker to show that a high-voltage power supply is >>>>>>> still dangerous. It should discharge the supply at some low current >>>>>>> and blink from, say, 1400 volts down to maybe 40. >>>>>> >>>>>> So, a series string of fifteen current-limit diodes running a capacitor- >>>>>> diac-LED blinkielight? S-272 seems suitable >>>>>> >>>>>> <https://www.mouser.com/datasheet/2/362/P22-23-CRD-1729293.pdf> >>>>> >>>>> The Supertex LND150 is a 500 volt depletion fet. A source resistor >>>>> will program the current, and they can apparently be strung in series >>>>> without problems. >>>>> >>>>> Three of them would do. They are around 30 cents each. >>>>> >>>>> A spin on Piglet's circuit might to the blinker. >>>>> >>>> >>>> I'd probably be happier with a gate bias string to force the voltages to >>>> equalize. Of course the resistors would have to be physically quite >>>> large to take the voltage. >>>> >> >>> >>> Somebody told me (was it you?) that they are OK in series. One or two >>> may avalanche somewhere above 500 volts and one will actually regulate >>> the current. I'm talking 50 or 100 uA in my case. >>> >>> >>> >> I've never used them above about 250V.> I tested one. It avalanches at 620 volts, no damage at low current. > > The gate zeners at about +-40, again no damage.Yabbut, at 1400V at least one and probably two of them will be continuously avalanching during normal operation, unless the drain curves are squishy enough to take up the unit-to-unit spread in I_DSS. (Maybe they are.) That would take a lot of testing to confirm as safe. The avalanche voltage increases with temperature, so there'd be no automatic sharing of dissipation. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●May 25, 20222022-05-25
On Wed, 25 May 2022 09:40:48 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>jlarkin@highlandsniptechnology.com wrote: >> On Tue, 24 May 2022 16:47:30 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> jlarkin@highlandsniptechnology.com wrote: >>>> On Tue, 24 May 2022 10:08:29 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> John Larkin wrote: >>>>>> On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whit3rd@gmail.com> >>>>>> wrote: >>>>>> >>>>>>> On Monday, May 23, 2022 at 10:19:30 AM UTC-7, John Larkin wrote: >>>>>>> >>>>>>>> I want an LED blinker to show that a high-voltage power supply is >>>>>>>> still dangerous. It should discharge the supply at some low current >>>>>>>> and blink from, say, 1400 volts down to maybe 40. >>>>>>> >>>>>>> So, a series string of fifteen current-limit diodes running a capacitor- >>>>>>> diac-LED blinkielight? S-272 seems suitable >>>>>>> >>>>>>> <https://www.mouser.com/datasheet/2/362/P22-23-CRD-1729293.pdf> >>>>>> >>>>>> The Supertex LND150 is a 500 volt depletion fet. A source resistor >>>>>> will program the current, and they can apparently be strung in series >>>>>> without problems. >>>>>> >>>>>> Three of them would do. They are around 30 cents each. >>>>>> >>>>>> A spin on Piglet's circuit might to the blinker. >>>>>> >>>>> >>>>> I'd probably be happier with a gate bias string to force the voltages to >>>>> equalize. Of course the resistors would have to be physically quite >>>>> large to take the voltage. >>>>> >>> >>>> >>>> Somebody told me (was it you?) that they are OK in series. One or two >>>> may avalanche somewhere above 500 volts and one will actually regulate >>>> the current. I'm talking 50 or 100 uA in my case. >>>> >>>> >>>> >>> I've never used them above about 250V. > >> I tested one. It avalanches at 620 volts, no damage at low current. >> >> The gate zeners at about +-40, again no damage. > >Yabbut, at 1400V at least one and probably two of them will be >continuously avalanching during normal operation, unless the drain >curves are squishy enough to take up the unit-to-unit spread in I_DSS. >(Maybe they are.) That would take a lot of testing to confirm as safe. > >The avalanche voltage increases with temperature, so there'd be no >automatic sharing of dissipation. > >Cheers > >Phil HobbsIf two avalanche at about 650 volts each, that runs the third one as the current limiter, at roughly 100 volts. Seems like it just works. At 100 uA, the two that avalanche dissipate maybe 65 mW each. The linear one is necessarily less. Now I need a good blinker circuit. -- Anybody can count to one. - Robert Widlar
Reply by ●May 25, 20222022-05-25
On Wed, 25 May 2022 11:21:22 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 23/05/2022 11:28 pm, John Larkin wrote: >> On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whit3rd@gmail.com> >> wrote: >> >>> On Monday, May 23, 2022 at 10:19:30 AM UTC-7, John Larkin wrote: >>> >>>> I want an LED blinker to show that a high-voltage power supply is >>>> still dangerous. It should discharge the supply at some low current >>>> and blink from, say, 1400 volts down to maybe 40. >>> >>> So, a series string of fifteen current-limit diodes running a capacitor- >>> diac-LED blinkielight? S-272 seems suitable >>> >>> <https://www.mouser.com/datasheet/2/362/P22-23-CRD-1729293.pdf> >> >> The Supertex LND150 is a 500 volt depletion fet. A source resistor >> will program the current, and they can apparently be strung in series >> without problems. >> >> Three of them would do. They are around 30 cents each. >> >> A spin on Piglet's circuit might to the blinker. >> > >My preference would be to skip the depletion fets and just use dropper >resistors - cheaper, more reliable, and best of all the non constant >blink rate gives a good visual confirmation that the HV capacitor is >actually discharging.The discharge would be a slow exponential and the blink rate would approach zero towards the end. Neither sounds good to me.> >Blinking could be as simple as a diac or bjt used as negistor. Spice >won't model E-B breakdown and reverse beta so can't simulate negistor >operation but breadboarding would be very quick. > >piglet-- Anybody can count to one. - Robert Widlar
Reply by ●May 25, 20222022-05-25
jlarkin@highlandsniptechnology.com wrote:> On Wed, 25 May 2022 09:40:48 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> jlarkin@highlandsniptechnology.com wrote: >>> On Tue, 24 May 2022 16:47:30 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> jlarkin@highlandsniptechnology.com wrote: >>>>> On Tue, 24 May 2022 10:08:29 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> John Larkin wrote: >>>>>>> On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whit3rd@gmail.com> >>>>>>> wrote: >>>>>>> >>>>>>>> On Monday, May 23, 2022 at 10:19:30 AM UTC-7, John Larkin wrote: >>>>>>>> >>>>>>>>> I want an LED blinker to show that a high-voltage power supply is >>>>>>>>> still dangerous. It should discharge the supply at some low current >>>>>>>>> and blink from, say, 1400 volts down to maybe 40. >>>>>>>> >>>>>>>> So, a series string of fifteen current-limit diodes running a capacitor- >>>>>>>> diac-LED blinkielight? S-272 seems suitable >>>>>>>> >>>>>>>> <https://www.mouser.com/datasheet/2/362/P22-23-CRD-1729293.pdf> >>>>>>> >>>>>>> The Supertex LND150 is a 500 volt depletion fet. A source resistor >>>>>>> will program the current, and they can apparently be strung in series >>>>>>> without problems. >>>>>>> >>>>>>> Three of them would do. They are around 30 cents each. >>>>>>> >>>>>>> A spin on Piglet's circuit might to the blinker. >>>>>>> >>>>>> >>>>>> I'd probably be happier with a gate bias string to force the voltages to >>>>>> equalize. Of course the resistors would have to be physically quite >>>>>> large to take the voltage. >>>>>> >>>> >>>>> >>>>> Somebody told me (was it you?) that they are OK in series. One or two >>>>> may avalanche somewhere above 500 volts and one will actually regulate >>>>> the current. I'm talking 50 or 100 uA in my case. >>>>> >>>>> >>>>> >>>> I've never used them above about 250V. >> >>> I tested one. It avalanches at 620 volts, no damage at low current. >>> >>> The gate zeners at about +-40, again no damage. >> >> Yabbut, at 1400V at least one and probably two of them will be >> continuously avalanching during normal operation, unless the drain >> curves are squishy enough to take up the unit-to-unit spread in I_DSS. >> (Maybe they are.) That would take a lot of testing to confirm as safe. >> >> The avalanche voltage increases with temperature, so there'd be no >> automatic sharing of dissipation.> > If two avalanche at about 650 volts each, that runs the third one as > the current limiter, at roughly 100 volts. Seems like it just works. > > At 100 uA, the two that avalanche dissipate maybe 65 mW each. The > linear one is necessarily less.Provided that there's no long-term damage mechanism. It's going to be in that state for a long long time.> Now I need a good blinker circuit.Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●May 25, 20222022-05-25
On Wednesday, 25 May 2022 at 06:41:00 UTC-7, Phil Hobbs wrote: ...> >>> Somebody told me (was it you?) that they are OK in series. One or two > >>> may avalanche somewhere above 500 volts and one will actually regulate > >>> the current. I'm talking 50 or 100 uA in my case. > >>> > >>> > >>> > >> I've never used them above about 250V. > > I tested one. It avalanches at 620 volts, no damage at low current. > > > > The gate zeners at about +-40, again no damage. > Yabbut, at 1400V at least one and probably two of them will be > continuously avalanching during normal operation, unless the drain > curves are squishy enough to take up the unit-to-unit spread in I_DSS. > (Maybe they are.) That would take a lot of testing to confirm as safe. > > The avalanche voltage increases with temperature, so there'd be no > automatic sharing of dissipation.... The Art of Electronics - The X Chapters. depicts that configuration and variants with a discussion in section 3.x.6.5 The simple configuration with just source resistors can have steps in the current as the voltage is varied as each device in turn avalanches. kw
Reply by ●May 25, 20222022-05-25
On Wed, 25 May 2022 09:22:48 -0700 (PDT), "ke...@kjwdesigns.com" <keith@kjwdesigns.com> wrote:>On Wednesday, 25 May 2022 at 06:41:00 UTC-7, Phil Hobbs wrote: >... >> >>> Somebody told me (was it you?) that they are OK in series. One or two >> >>> may avalanche somewhere above 500 volts and one will actually regulate >> >>> the current. I'm talking 50 or 100 uA in my case. >> >>> >> >>> >> >>> >> >> I've never used them above about 250V. >> > I tested one. It avalanches at 620 volts, no damage at low current. >> > >> > The gate zeners at about +-40, again no damage. >> Yabbut, at 1400V at least one and probably two of them will be >> continuously avalanching during normal operation, unless the drain >> curves are squishy enough to take up the unit-to-unit spread in I_DSS. >> (Maybe they are.) That would take a lot of testing to confirm as safe. >> >> The avalanche voltage increases with temperature, so there'd be no >> automatic sharing of dissipation. >... > >The Art of Electronics - The X Chapters. depicts that configuration and variants with a discussion in section 3.x.6.5 > >The simple configuration with just source resistors can have steps in the current as the voltage is varied as each device in turn avalanches. > >kwThe simple version, 3x57a with LND150s would be fine for a 1400 volt LED blinker. And there are some diacs that would work for the periodic cap discharge into the LED. 9 or so parts total. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
Reply by ●May 25, 20222022-05-25
John Larkin wrote:> The simple version, 3x57a with LND150s would be fine for a 1400 volt > LED blinker.Why wouldn't you just use a 1.7kV+ rated DMOS? Best regards, Piotr
Reply by ●May 25, 20222022-05-25
On Wed, 25 May 2022 20:31:12 +0200, Piotr Wyderski <bombald@protonmail.com> wrote:>John Larkin wrote: > >> The simple version, 3x57a with LND150s would be fine for a 1400 volt >> LED blinker. > >Why wouldn't you just use a 1.7kV+ rated DMOS? > > Best regards, PiotrHad a part in mind? If it's enhancement mode, it will need something to bias it up. We do have the LND150s in stock, SOT23 package. -- Anybody can count to one. - Robert Widlar
Reply by ●May 26, 20222022-05-26
jlarkin@highlandsniptechnology.com wrote:> Had a part in mind? If it's enhancement mode, it will need something > to bias it up. > > We do have the LND150s in stock, SOT23 package.Mouser has this IXTA1N170DHV. More expensive that LND150, but I am not sure if a safety circuit is the best place for savings and IIRC your business is of the high-added-value/low volume profile anyway. Just saying, it's your decision. I use the IXTA08N100D2HV for the same purpose (have a blinker too, and a buzzer specifically tuned to emulate a fighter jet warning system: https://youtu.be/fd50GtnXR7Y?t=1145, just couldn't resist), but my cap voltage is under 900V, 650V typical. Best regards, Piotr
