BJT behaviour at ridiculously low current levels...

J

John Larkin

Guest
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
 
P

Piotr Wyderski

Guest
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
 
W

whit3rd

Guest
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.
 
J

John Walliker

Guest
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
 
S

server

Guest
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.

John

Mouser 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
 
P

Phil Hobbs

Guest
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
 
J

John Walliker

Guest
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
 
P

Phil Hobbs

Guest
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
 
J

John Walliker

Guest
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
 
S

server

Guest
On Tue, 24 May 2022 10:43:08 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

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.

Rarely! But we\'re using a TO-92 LM35 to measure the temp of a CPU
cooler that we\'re using as a mosfet heat sink. We\'ll glue it to the
side of the cooler and plug it into three little pin sockets.

Cheers

Phil Hobbs

(Who just designed one into a supply-dictated board spin.) :(

Are TO-92s easier to get than surfmount parts? At least it\'s an
option.



--

Anybody can count to one.

- Robert Widlar
 
S

server

Guest
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.

Cheers

Phil Hobbs

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.



--

Anybody can count to one.

- Robert Widlar
 
J

John Larkin

Guest
On Tue, 24 May 2022 07:25:20 -0700 (PDT), John Walliker
<jrwalliker@gmail.com> wrote:

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

We have 2500 in stock. I could spare a few to anyone who wants to play
with them.

--

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
 
J

John Larkin

Guest
On Tue, 24 May 2022 09:07:34 -0700 (PDT), John Walliker
<jrwalliker@gmail.com> wrote:

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

Just put them in parallel on the schematic.

--

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
 

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