avalanche transistors...

[Tim Williams]

\"Gerhard Hoffmann\" <dk4xp@arcor.de> wrote in message
news:rf81vd$j5v$1@solani.org...

Am 22.07.20 um 02:06 schrieb Tim Williams:
Sure. Works fine, but you get N * Rds(on) as it were, and if your load
is 50 ohms or whatever regardless of stack height, well...

I don\'t think that in avalanche breakdown the transistor
has much Rce. It\'s beyond ON.

2N3904s are about 10 ohms. It seems Rce isn\'t enhanced much -- avalanche
does not, a UJT, make. (Related note: JFETs don\'t seem to enhance much when
the gate is forward-biased, at least not the common types I tried. A shame;
I recall reading that UJTs are basically failed JFETs (unable to pinch off),
would be fun if it actually worked.)

The better types have lower resistance, but still a nonzero amount. The
point of diminishing returns is easily calculated, in any case, once this is
known.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

\"Gerhard Hoffmann\" <dk4xp@arcor.de> wrote in message
news:rf81vd$j5v$1@solani.org...

Am 22.07.20 um 02:06 schrieb Tim Williams:
Sure. Works fine, but you get N * Rds(on) as it were, and if your load
is 50 ohms or whatever regardless of stack height, well...

I don\'t think that in avalanche breakdown the transistor
has much Rce. It\'s beyond ON.

2N3904s are about 10 ohms. It seems Rce isn\'t enhanced much -- avalanche
does not, a UJT, make. (Related note: JFETs don\'t seem to enhance much when
the gate is forward-biased, at least not the common types I tried. A shame;
I recall reading that UJTs are basically failed JFETs (unable to pinch off),
would be fun if it actually worked.)

The better types have lower resistance, but still a nonzero amount. The
point of diminishing returns is easily calculated, in any case, once this is
known.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

\"Gerhard Hoffmann\" <dk4xp@arcor.de> wrote in message
news:rf81vd$j5v$1@solani.org...

Am 22.07.20 um 02:06 schrieb Tim Williams:
Sure. Works fine, but you get N * Rds(on) as it were, and if your load
is 50 ohms or whatever regardless of stack height, well...

I don\'t think that in avalanche breakdown the transistor
has much Rce. It\'s beyond ON.

2N3904s are about 10 ohms. It seems Rce isn\'t enhanced much -- avalanche
does not, a UJT, make. (Related note: JFETs don\'t seem to enhance much when
the gate is forward-biased, at least not the common types I tried. A shame;
I recall reading that UJTs are basically failed JFETs (unable to pinch off),
would be fun if it actually worked.)

The better types have lower resistance, but still a nonzero amount. The
point of diminishing returns is easily calculated, in any case, once this is
known.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

\"bitrex\" <user@example.net> wrote in message
news:zi0SG.12332$Wl7.10992@fx26.iad...

The ol\' 2D21 thyratrons, gas tube relay triggers for like jukeboxes and
stuff I guess, had very fast (ionization? de-ionization?) times for their
era. I dunno what the equivalent slew rate is exactly but the rising edge
on a relaxation sawtooth is fast enough that divided down the usual
jellybean opamps as unity-buffers with GBWs of 10s of MHz and
10 or 20 volt/usec slew rates can\'t keep up.

Fractional microsecond. Very similar to SCRs actually, and for very similar
physical reasons, I suppose.

Deionization is slow as balls, milliseconds. Xenon (2D21 and such) and
mercury (bigger power thyratrons) are very slow ions. Hydrogen, or
deuterium for that matter, is the fast one, with nanoseconds risetime and, I
forget what exactly, fractional microsecond deionization?

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[John Larkin]

On Thu, 23 Jul 2020 02:31:36 -0500, \"Tim Williams\"
<tiwill@seventransistorlabs.com> wrote:

\"Gerhard Hoffmann\" <dk4xp@arcor.de> wrote in message
news:rf81vd$j5v$1@solani.org...
Am 22.07.20 um 02:06 schrieb Tim Williams:
Sure. Works fine, but you get N * Rds(on) as it were, and if your load
is 50 ohms or whatever regardless of stack height, well...

I don\'t think that in avalanche breakdown the transistor
has much Rce. It\'s beyond ON.

2N3904s are about 10 ohms. It seems Rce isn\'t enhanced much -- avalanche
does not, a UJT, make. (Related note: JFETs don\'t seem to enhance much when
the gate is forward-biased, at least not the common types I tried.

I have seen mesfets and phemts turn on radically as the gate starts to
conduct. Almost a bipolar effect.

JFETS and depletion phemts do enhance a little. A depletion phemt Ron
can be reduced about in half from the zero gate voltage value.

The Supertex depletion mosfets enhance too.

 

[John Larkin]

On Thu, 23 Jul 2020 02:31:36 -0500, \"Tim Williams\"
<tiwill@seventransistorlabs.com> wrote:

\"Gerhard Hoffmann\" <dk4xp@arcor.de> wrote in message
news:rf81vd$j5v$1@solani.org...
Am 22.07.20 um 02:06 schrieb Tim Williams:
Sure. Works fine, but you get N * Rds(on) as it were, and if your load
is 50 ohms or whatever regardless of stack height, well...

I don\'t think that in avalanche breakdown the transistor
has much Rce. It\'s beyond ON.

2N3904s are about 10 ohms. It seems Rce isn\'t enhanced much -- avalanche
does not, a UJT, make. (Related note: JFETs don\'t seem to enhance much when
the gate is forward-biased, at least not the common types I tried.

I have seen mesfets and phemts turn on radically as the gate starts to
conduct. Almost a bipolar effect.

JFETS and depletion phemts do enhance a little. A depletion phemt Ron
can be reduced about in half from the zero gate voltage value.

The Supertex depletion mosfets enhance too.

 

[John Larkin]

On Thu, 23 Jul 2020 02:31:36 -0500, \"Tim Williams\"
<tiwill@seventransistorlabs.com> wrote:

\"Gerhard Hoffmann\" <dk4xp@arcor.de> wrote in message
news:rf81vd$j5v$1@solani.org...
Am 22.07.20 um 02:06 schrieb Tim Williams:
Sure. Works fine, but you get N * Rds(on) as it were, and if your load
is 50 ohms or whatever regardless of stack height, well...

I don\'t think that in avalanche breakdown the transistor
has much Rce. It\'s beyond ON.

2N3904s are about 10 ohms. It seems Rce isn\'t enhanced much -- avalanche
does not, a UJT, make. (Related note: JFETs don\'t seem to enhance much when
the gate is forward-biased, at least not the common types I tried.

I have seen mesfets and phemts turn on radically as the gate starts to
conduct. Almost a bipolar effect.

JFETS and depletion phemts do enhance a little. A depletion phemt Ron
can be reduced about in half from the zero gate voltage value.

The Supertex depletion mosfets enhance too.

 

[bitrex]

On 7/23/2020 6:19 PM, Tim Williams wrote:

\"bitrex\" <user@example.net> wrote in message
news:zi0SG.12332$Wl7.10992@fx26.iad...
The ol\' 2D21 thyratrons, gas tube relay triggers for like jukeboxes and
stuff I guess, had very fast (ionization? de-ionization?) times for
their era. I dunno what the equivalent slew rate is exactly but the
rising edge on a relaxation sawtooth is fast enough that divided down
the usual jellybean opamps as unity-buffers with GBWs of 10s of MHz and
10 or 20 volt/usec slew rates can\'t keep up.

Fractional microsecond.  Very similar to SCRs actually, and for very
similar physical reasons, I suppose.

Deionization is slow as balls, milliseconds.  Xenon (2D21 and such) and
mercury (bigger power thyratrons) are very slow ions.  Hydrogen, or
deuterium for that matter, is the fast one, with nanoseconds risetime
and, I forget what exactly, fractional microsecond deionization?

Tim

Heh, gassy tubes!

<http://www.quickmeme.com/img/e1/e1ba8d81df7b145e5c72191ad5bd39333af9f3196bbc681d4fb28086fa490eff.jpg>