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>
BJT behaviour at ridiculously low current levels
Started by ●May 11, 2022
Reply by ●May 23, 20222022-05-23
Reply by ●May 23, 20222022-05-23
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. -- 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 24, 20222022-05-24
John Larkin wrote:> A spin on Piglet's circuit might to the blinker.It might, but Piglet's circuit excels at low power. This is not what you want to discharge a capacitor. Just power a 3V3-12V zener through your DMOS at the highest possible current limited by its thermal SOA and power any blinker from that zener. Plenty of free milliwatts to burn. Best regards, Piotr
Reply by ●May 24, 20222022-05-24
On Monday, May 23, 2022 at 3:29:10 PM UTC-7, John Larkin wrote:> On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whi...@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.Yeah, and a 'current-limit diode' is also a depletion FET. With a zener limit specified (I'm not sure about LND150). Multiples only share the voltage with such a matching zener specification. A resistor would work, too, but the alarm blinkie would change frequency dramatically.
Reply by ●May 24, 20222022-05-24
On Tuesday, 24 May 2022 at 09:08:21 UTC+1, whit3rd wrote:> On Monday, May 23, 2022 at 3:29:10 PM UTC-7, John Larkin wrote: > > On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whi...@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. > Yeah, and a 'current-limit diode' is also a depletion FET. With a zener > limit specified (I'm not sure about LND150). Multiples only share > the voltage with such a matching zener specification. > > A resistor would work, too, but the alarm blinkie would change frequency > dramatically.Does anyone actually sell surface mount LND150s at the moment? All the usual suppliers seem to be out of stock for at least several months. John
Reply by ●May 24, 20222022-05-24
On Tue, 24 May 2022 05:53:02 -0700 (PDT), John Walliker <jrwalliker@gmail.com> wrote:>On Tuesday, 24 May 2022 at 09:08:21 UTC+1, whit3rd wrote: >> On Monday, May 23, 2022 at 3:29:10 PM UTC-7, John Larkin wrote: >> > On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whi...@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. >> Yeah, and a 'current-limit diode' is also a depletion FET. With a zener >> limit specified (I'm not sure about LND150). Multiples only share >> the voltage with such a matching zener specification. >> >> A resistor would work, too, but the alarm blinkie would change frequency >> dramatically. > >Does anyone actually sell surface mount LND150s at the moment? All >the usual suppliers seem to be out of stock for at least several months. > >JohnMouser has LND250s, basically the same part. A current sink is a great way to discharge a power supply. No long exponential tail. In series with an LED, brigntness is constant until it hits bottom and winks out. My HV blinker would be similar, constant blink rate all the way down. -- Anybody can count to one. - Robert Widlar
Reply by ●May 24, 20222022-05-24
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. 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 24, 20222022-05-24
On Tuesday, 24 May 2022 at 15:05:31 UTC+1, jla...@highlandsniptechnology.com wrote:> On Tue, 24 May 2022 05:53:02 -0700 (PDT), John Walliker> >Does anyone actually sell surface mount LND150s at the moment? All > >the usual suppliers seem to be out of stock for at least several months. > > > >John > Mouser has LND250s, basically the same part.Thank you - John
Reply by ●May 24, 20222022-05-24
John Walliker wrote:> On Tuesday, 24 May 2022 at 09:08:21 UTC+1, whit3rd wrote: >> On Monday, May 23, 2022 at 3:29:10 PM UTC-7, John Larkin wrote: >>> On Mon, 23 May 2022 11:06:00 -0700 (PDT), whit3rd <whi...@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. >> Yeah, and a 'current-limit diode' is also a depletion FET. With a zener >> limit specified (I'm not sure about LND150). Multiples only share >> the voltage with such a matching zener specification. >> >> A resistor would work, too, but the alarm blinkie would change frequency >> dramatically. > > Does anyone actually sell surface mount LND150s at the moment? All > the usual suppliers seem to be out of stock for at least several months. > > John >TO-92s are good for the soul. Cheers Phil Hobbs (Who just designed one into a supply-dictated board spin.) :( -- 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 24, 20222022-05-24
On Tuesday, 24 May 2022 at 15:43:20 UTC+1, Phil Hobbs wrote:> John Walliker wrote:> > Does anyone actually sell surface mount LND150s at the moment? All > > the usual suppliers seem to be out of stock for at least several months. > > > > John > > > TO-92s are good for the soul.Maybe I should create a composite SOT-23/TO-92 footprint "just in case". John
