need really bad diode...

J

John Larkin

Guest
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.
 
John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.
Click to expand...

A BAV99 is even worse, once it warms up a bit (1.05V typ at 100 mA and
40C). I bet you have 30k of them in stock, amirite? They also come in
SC70.

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
 
On Tue, 20 Sep 2022 15:49:14 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.


A BAV99 is even worse, once it warms up a bit (1.05V typ at 100 mA and
40C). I bet you have 30k of them in stock, amirite? They also come in
SC70.

Cheers

Phil Hobbs
Click to expand...

SOT-23, only 2300! But it is an impressively bad diode.

SiC would work, but they are impressively(expensive + unavailable)
 
On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.
Click to expand...

Think of some other way. Diode solutions aren\'t all they\'re cracked up to be.
 
On 9/20/2022 21:04, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.
Click to expand...

I am sure you\'ll find your way with the problem calling for the
diode without any help.
I am going to insert a rant-ish comment about the \"long story\".

Every time I have used some readily available convertor part,
LTC, Maxim many ears earlier, there were long stories.
Which is why to this day I make my own regulators, 1/2 74hc123
and 1/2 lmc6482, typically. Plus a mosfet and its driver of course.
Somewhat more complex and the story may be long again on
some occasions but the ending is happy and calls for a lot
less compromise. Having control over the loop overall etc.
gives you that.
 
On Tue, 20 Sep 2022 13:46:39 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.

Think of some other way. Diode solutions aren\'t all they\'re cracked up to be.
Click to expand...

I just need to drop about a volt. A diode would do that just fine.
Better yet 2 diodes in series so I can tune the drop.

https://www.dropbox.com/s/j72tytvzae0ubf2/T660_Regs_Sep_20.jpg?raw=1

Reg3 has an abs max input of 6 volts. I want at least 6.5 for my
linear regs. I can\'t use 3.3 as the input to reg3 because +1 FPGA core
has to come up before 3.3.
 
On Wed, 21 Sep 2022 00:13:29 +0300, Dimiter_Popoff <dp@tgi-sci.com>
wrote:

On 9/20/2022 21:04, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.


I am sure you\'ll find your way with the problem calling for the
diode without any help.
Click to expand...

It\'s an electronic discussion group! In theory at least. Sometimes.

I am going to insert a rant-ish comment about the \"long story\".

Every time I have used some readily available convertor part,
LTC, Maxim many ears earlier, there were long stories.
Which is why to this day I make my own regulators, 1/2 74hc123
and 1/2 lmc6482, typically. Plus a mosfet and its driver of course.
Somewhat more complex and the story may be long again on
some occasions but the ending is happy and calls for a lot
less compromise. Having control over the loop overall etc.
gives you that.
Click to expand...

Home-made is a lot of parts. Lots of integrated switchers work fine.

Synchronous switchers can have bad EMI issues.

Some parts are poorly defined as regards cap ESR and loop stability.

Best to breadboard.
 
On 9/21/2022 0:59, John Larkin wrote:
On Wed, 21 Sep 2022 00:13:29 +0300, Dimiter_Popoff <dp@tgi-sci.com
wrote:

On 9/20/2022 21:04, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.


I am sure you\'ll find your way with the problem calling for the
diode without any help.

It\'s an electronic discussion group! In theory at least. Sometimes.
Click to expand...

I was just making an excuse for the rant I was about to post, of course
I did not mean your post was inappropriate, quite the contrary.

I am going to insert a rant-ish comment about the \"long story\".

Every time I have used some readily available convertor part,
LTC, Maxim many ears earlier, there were long stories.
Which is why to this day I make my own regulators, 1/2 74hc123
and 1/2 lmc6482, typically. Plus a mosfet and its driver of course.
Somewhat more complex and the story may be long again on
some occasions but the ending is happy and calls for a lot
less compromise. Having control over the loop overall etc.
gives you that.

Home-made is a lot of parts. Lots of integrated switchers work fine.
Click to expand...

They take more part obviously but they don\'t take a much larger area
on the board. I am sure lots of integrated switchers work fine, and
the few (not more than 5-6) I remember using did work but had either
stability issues or noise or whatever, I don\'t remember, I only
remember there were issues beyond my control as they were integrated.
I may have been too demanding, of course.

Synchronous switchers can have bad EMI issues.

Some parts are poorly defined as regards cap ESR and loop stability.

Best to breadboard.
Click to expand...

Breadboard does not help much with switchers where routing is essential.
But I have found out that even for my \"home made\" switchers ltspice is
reasonably accurate evaluating stability over load and input variations,
as well as step response etc.
 
On 9/20/22 17:20, John Larkin wrote:
On Tue, 20 Sep 2022 13:46:39 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.

Think of some other way. Diode solutions aren\'t all they\'re cracked up to be.

I just need to drop about a volt. A diode would do that just fine.
Better yet 2 diodes in series so I can tune the drop.

https://www.dropbox.com/s/j72tytvzae0ubf2/T660_Regs_Sep_20.jpg?raw=1

Reg3 has an abs max input of 6 volts. I want at least 6.5 for my
linear regs. I can\'t use 3.3 as the input to reg3 because +1 FPGA core
has to come up before 3.3.
Click to expand...

resistor and 5ish volt zener to ground?

--
Regards,
Carl
 
On Tuesday, September 20, 2022 at 11:04:11 AM UTC-7, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.
Click to expand...

Or, a diode and 10 ohm resistor in series.

The structure of a PIN diode should give fairly high forward resistivity,
though I\'m not sure where that\'d be found in a datasheet.
 
On Wed, 21 Sep 2022 01:22:36 +0300, Dimiter_Popoff <dp@tgi-sci.com>
wrote:

On 9/21/2022 0:59, John Larkin wrote:
On Wed, 21 Sep 2022 00:13:29 +0300, Dimiter_Popoff <dp@tgi-sci.com
wrote:

On 9/20/2022 21:04, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.


I am sure you\'ll find your way with the problem calling for the
diode without any help.

It\'s an electronic discussion group! In theory at least. Sometimes.

I was just making an excuse for the rant I was about to post, of course
I did not mean your post was inappropriate, quite the contrary.


I am going to insert a rant-ish comment about the \"long story\".

Every time I have used some readily available convertor part,
LTC, Maxim many ears earlier, there were long stories.
Which is why to this day I make my own regulators, 1/2 74hc123
and 1/2 lmc6482, typically. Plus a mosfet and its driver of course.
Somewhat more complex and the story may be long again on
some occasions but the ending is happy and calls for a lot
less compromise. Having control over the loop overall etc.
gives you that.

Home-made is a lot of parts. Lots of integrated switchers work fine.

They take more part obviously but they don\'t take a much larger area
on the board. I am sure lots of integrated switchers work fine, and
the few (not more than 5-6) I remember using did work but had either
stability issues or noise or whatever, I don\'t remember, I only
remember there were issues beyond my control as they were integrated.
I may have been too demanding, of course.


Synchronous switchers can have bad EMI issues.

Some parts are poorly defined as regards cap ESR and loop stability.

Best to breadboard.


Breadboard does not help much with switchers where routing is essential.
But I have found out that even for my \"home made\" switchers ltspice is
reasonably accurate evaluating stability over load and input variations,
as well as step response etc.
Click to expand...

I really like TPS54302. It\'s a tiny SOT23 switcher, spread-spectrum,
well behaved. But I can\'t get the TI Pspice model to work in LT Spice
and I haven\'t the energy to learn Tina. I\'ll breadboard it.

I think I can use it as a +7 to -7 converter.
 
On Tue, 20 Sep 2022 18:23:56 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Tuesday, September 20, 2022 at 11:04:11 AM UTC-7, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

Or, a diode and 10 ohm resistor in series.

The structure of a PIN diode should give fairly high forward resistivity,
though I\'m not sure where that\'d be found in a datasheet.
Click to expand...

HV diodes are usually PINs. That shows up in the I:V curve.
 
On Tuesday, September 20, 2022 at 9:33:17 PM UTC-4, John Larkin wrote:
On Wed, 21 Sep 2022 01:22:36 +0300, Dimiter_Popoff <d...@tgi-sci.com
wrote:

On 9/21/2022 0:59, John Larkin wrote:
On Wed, 21 Sep 2022 00:13:29 +0300, Dimiter_Popoff <d...@tgi-sci.com
wrote:

On 9/20/2022 21:04, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.


I am sure you\'ll find your way with the problem calling for the
diode without any help.

It\'s an electronic discussion group! In theory at least. Sometimes.

I was just making an excuse for the rant I was about to post, of course
I did not mean your post was inappropriate, quite the contrary.


I am going to insert a rant-ish comment about the \"long story\".

Every time I have used some readily available convertor part,
LTC, Maxim many ears earlier, there were long stories.
Which is why to this day I make my own regulators, 1/2 74hc123
and 1/2 lmc6482, typically. Plus a mosfet and its driver of course.
Somewhat more complex and the story may be long again on
some occasions but the ending is happy and calls for a lot
less compromise. Having control over the loop overall etc.
gives you that.

Home-made is a lot of parts. Lots of integrated switchers work fine.

They take more part obviously but they don\'t take a much larger area
on the board. I am sure lots of integrated switchers work fine, and
the few (not more than 5-6) I remember using did work but had either
stability issues or noise or whatever, I don\'t remember, I only
remember there were issues beyond my control as they were integrated.
I may have been too demanding, of course.


Synchronous switchers can have bad EMI issues.

Some parts are poorly defined as regards cap ESR and loop stability.

Best to breadboard.


Breadboard does not help much with switchers where routing is essential.
But I have found out that even for my \"home made\" switchers ltspice is
reasonably accurate evaluating stability over load and input variations,
as well as step response etc.
I really like TPS54302. It\'s a tiny SOT23 switcher, spread-spectrum,
well behaved. But I can\'t get the TI Pspice model to work in LT Spice
and I haven\'t the energy to learn Tina. I\'ll breadboard it.

I think I can use it as a +7 to -7 converter.
Click to expand...

https://webench.ti.com/power-designer/switching-regulator/export/217?noparams=0
Export LM25088MH-1/NOPB ‑ 7V-7V to -7.00V @ 2A

cheers
 
On a sunny day (Tue, 20 Sep 2022 11:04:03 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<akvjih1eeavtfqhlb82igfe28tvg8br8i5@4ax.com>:

I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.
Click to expand...

Old color sets had a 4 kV rectfer for focus, consisted
of a ceramic tube with a zillion ? diodes in series
https://www.ebay.com/itm/192966681173?hash=item2cedb5e255:g:FqgAAOSwxhNjE38d&_trksid=p5731.m3795
https://www.ebay.com/itm/194844748455

;-)
 
On Wed, 21 Sep 2022 05:04:36 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Tue, 20 Sep 2022 11:04:03 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
akvjih1eeavtfqhlb82igfe28tvg8br8i5@4ax.com>:

I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.

Old color sets had a 4 kV rectfer for focus, consisted
of a ceramic tube with a zillion ? diodes in series
https://www.ebay.com/itm/192966681173?hash=item2cedb5e255:g:FqgAAOSwxhNjE38d&_trksid=p5731.m3795
https://www.ebay.com/itm/194844748455

;-)
Click to expand...

I think one plate/junction of a selenium rectifier dropped about 2
volts.
 
On Tue, 20 Sep 2022 19:17:12 -0700 (PDT), Anahid Naryman
<anaryman@gmail.com> wrote:

On Tuesday, September 20, 2022 at 9:33:17 PM UTC-4, John Larkin wrote:
On Wed, 21 Sep 2022 01:22:36 +0300, Dimiter_Popoff <d...@tgi-sci.com
wrote:

On 9/21/2022 0:59, John Larkin wrote:
On Wed, 21 Sep 2022 00:13:29 +0300, Dimiter_Popoff <d...@tgi-sci.com
wrote:

On 9/20/2022 21:04, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.


I am sure you\'ll find your way with the problem calling for the
diode without any help.

It\'s an electronic discussion group! In theory at least. Sometimes.

I was just making an excuse for the rant I was about to post, of course
I did not mean your post was inappropriate, quite the contrary.


I am going to insert a rant-ish comment about the \"long story\".

Every time I have used some readily available convertor part,
LTC, Maxim many ears earlier, there were long stories.
Which is why to this day I make my own regulators, 1/2 74hc123
and 1/2 lmc6482, typically. Plus a mosfet and its driver of course.
Somewhat more complex and the story may be long again on
some occasions but the ending is happy and calls for a lot
less compromise. Having control over the loop overall etc.
gives you that.

Home-made is a lot of parts. Lots of integrated switchers work fine.

They take more part obviously but they don\'t take a much larger area
on the board. I am sure lots of integrated switchers work fine, and
the few (not more than 5-6) I remember using did work but had either
stability issues or noise or whatever, I don\'t remember, I only
remember there were issues beyond my control as they were integrated.
I may have been too demanding, of course.


Synchronous switchers can have bad EMI issues.

Some parts are poorly defined as regards cap ESR and loop stability.

Best to breadboard.


Breadboard does not help much with switchers where routing is essential.
But I have found out that even for my \"home made\" switchers ltspice is
reasonably accurate evaluating stability over load and input variations,
as well as step response etc.
I really like TPS54302. It\'s a tiny SOT23 switcher, spread-spectrum,
well behaved. But I can\'t get the TI Pspice model to work in LT Spice
and I haven\'t the energy to learn Tina. I\'ll breadboard it.

I think I can use it as a +7 to -7 converter.


https://webench.ti.com/power-designer/switching-regulator/export/217?noparams=0
Export LM25088MH-1/NOPB ? 7V-7V to -7.00V @ 2A

cheers
Click to expand...

Webench requires a login (why make people log in to sell stuff?) and
doesn\'t work on my machines.

I suspect that LT Spice added a couple billion dollars to ADI\'s
purchase price of LT. And it crushed the sales of several expensive
simulators. Mike E says that LT Spice is used 1000 times more than all
other circuut sim programs.

There are advantages to breadboarding tricky stuff like switchers,
even if the sims work. EMI. Thermals. Caps. Inductors. Reality.

https://www.dropbox.com/sh/ajtqs7c1nswfhey/AABi7r0gchljjrxka4aHZItfa?dl=0

https://www.dropbox.com/sh/8nd4dibu77znh44/AAAkO6lEHy9FZ50od2-mqt0va?dl=0

Actually, I have a LOT of test data on TPS54302, just none for the
inverter case.

Someone used to sell a pseudorandom noise generator chip. This is one!
 
tirsdag den 20. september 2022 kl. 23.20.55 UTC+2 skrev John Larkin:
On Tue, 20 Sep 2022 13:46:39 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.

Think of some other way. Diode solutions aren\'t all they\'re cracked up to be.
I just need to drop about a volt. A diode would do that just fine.
Better yet 2 diodes in series so I can tune the drop.
Click to expand...

NPN and two resistors?
 
On a sunny day (Wed, 21 Sep 2022 07:34:49 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<d58mih9ta0jghuks7ibflhguba17jim6bl@4ax.com>:

On Wed, 21 Sep 2022 05:04:36 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Tue, 20 Sep 2022 11:04:03 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
akvjih1eeavtfqhlb82igfe28tvg8br8i5@4ax.com>:

I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.

Old color sets had a 4 kV rectfer for focus, consisted
of a ceramic tube with a zillion ? diodes in series
https://www.ebay.com/itm/192966681173?hash=item2cedb5e255:g:FqgAAOSwxhNjE38d&_trksid=p5731.m3795
https://www.ebay.com/itm/194844748455

;-)

I think one plate/junction of a selenium rectifier dropped about 2
volts.
Click to expand...

You could make something with a transistor Vbe and diode in series:
|
___
\\ /
---
|
_________
| |
| |
[ ] X |c
| |/
|------| NPN
| |\\/e
[ ] 1k |
| |
---------
|
 
On Wed, 21 Sep 2022 16:19:14 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Wed, 21 Sep 2022 07:34:49 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
d58mih9ta0jghuks7ibflhguba17jim6bl@4ax.com>:

On Wed, 21 Sep 2022 05:04:36 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Tue, 20 Sep 2022 11:04:03 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
akvjih1eeavtfqhlb82igfe28tvg8br8i5@4ax.com>:

I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.

Old color sets had a 4 kV rectfer for focus, consisted
of a ceramic tube with a zillion ? diodes in series
https://www.ebay.com/itm/192966681173?hash=item2cedb5e255:g:FqgAAOSwxhNjE38d&_trksid=p5731.m3795
https://www.ebay.com/itm/194844748455

;-)

I think one plate/junction of a selenium rectifier dropped about 2
volts.

You could make something with a transistor Vbe and diode in series:
|
___
\\ /
---
|
_________
| |
| |
[ ] X |c
| |/
|------| NPN
| |\\/e
[ ] 1k |
| |
---------
|
Click to expand...

Yes, there are lots of ways to use a transistor here. Don\'t need the
upper series diode.

A small Darlington would give me more drop. Or one of those \"logic
transistors\" with internal resistors.

The only darls we have in stock are ancient TO-92, hand load and
solder stuff. Yuk. Mosfets pretty much made darlingtons obsolete.

A logic-threshold mosfet like FDV301, drain to gate, would sort of
work. Roughly 2 volts at 200 mA; 400 mW is a bit much for a SOT23.
 
On Wed, 21 Sep 2022 08:38:43 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

tirsdag den 20. september 2022 kl. 23.20.55 UTC+2 skrev John Larkin:
On Tue, 20 Sep 2022 13:46:39 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote:
I want lots of voltage drop at 100 mA or so.

A high voltage fast-recovery diode, like ES1G, might work.

I suppose I could just put two ES1Gs in series, but that\'s not
sporting.

MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop
about 2 volts at 100 mA!

This is a supply sequencing dilemma with the LT6803. A long story.

Think of some other way. Diode solutions aren\'t all they\'re cracked up to be.
I just need to drop about a volt. A diode would do that just fine.
Better yet 2 diodes in series so I can tune the drop.

NPN and two resistors?
Click to expand...

That would work, but is more parts than two diodes. I\'d probably need
something bigger than a SOT23.
 
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