current regulator

[John Larkin]

https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Phil Hobbs]

On 05/30/2018 11:23 AM, John Larkin wrote:

https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[George Herold]

On Wednesday, May 30, 2018 at 12:09:37 PM UTC-4, Phil Hobbs wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Way too much current for the Spad. The spec sheet says ~200uA CW
I've got an lnd150 and 10k ohm (G-S) for 100uA. (It's a few hundred
volts, 100V @ 100 uA ~10 mW... it might take more than that but who wants
to blow up a $250 part, I've been afraid to test the current limit until
I make more measurements.)

George H.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

On 05/31/2018 08:30 AM, George Herold wrote:

On Wednesday, May 30, 2018 at 12:09:37 PM UTC-4, Phil Hobbs wrote:
On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.
Way too much current for the Spad. The spec sheet says ~200uA CW
I've got an lnd150 and 10k ohm (G-S) for 100uA. (It's a few hundred
volts, 100V @ 100 uA ~10 mW... it might take more than that but who wants
to blow up a $250 part, I've been afraid to test the current limit until
I make more measurements.)

I was talking about the safety current limit, not the device protection
one. Unless I'm mistaken, UL wants the gizmo to be safe even when it's
broken.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

On 05/30/2018 07:59 PM, John Larkin wrote:

On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.

I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

Do you find that it's consistent enough in real life to make a good
current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks
like about 35 ohms at room temperature, which wouldn't be bad for input
protection of lowish-noise amps.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

On Thursday, May 31, 2018 at 9:19:29 AM UTC-4, Phil Hobbs wrote:

On 05/31/2018 08:30 AM, George Herold wrote:
On Wednesday, May 30, 2018 at 12:09:37 PM UTC-4, Phil Hobbs wrote:
On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.
Way too much current for the Spad. The spec sheet says ~200uA CW
I've got an lnd150 and 10k ohm (G-S) for 100uA. (It's a few hundred
volts, 100V @ 100 uA ~10 mW... it might take more than that but who wants
to blow up a $250 part, I've been afraid to test the current limit until
I make more measurements.)


I was talking about the safety current limit, not the device protection
one. Unless I'm mistaken, UL wants the gizmo to be safe even when it's
broken.

Oh right, something like 10 mA might be perfect for that.
I haven't thought that far our yet. Heck at the moment I'm using
a hunking linear HV supply, and haven't made the HV power supply....
Lot's to do.

George h.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

On Thursday, May 31, 2018 at 10:45:04 AM UTC-4, Phil Hobbs wrote:

On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

I bought DN2540's -1.5 to -3.5V.. but that's no different than the
lnd150's spread. Have you measured any?

Hmmm if I get a batch of lnd150's with closer to -3V than whatever
I'm seeing now that could be a problem.

I'll have to measure some... I'm mostly machining today. I found this
2-56 gun tap in our drawer. It's really slick, shoots the chip out the
far end of the hole, rather than having to work the tap in and out.
(Wouldn't be so good for a blind tapped hole though.)

George H.

Do you find that it's consistent enough in real life to make a good
current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks
like about 35 ohms at room temperature, which wouldn't be bad for input
protection of lowish-noise amps.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

On 05/31/2018 01:12 PM, George Herold wrote:

On Thursday, May 31, 2018 at 10:45:04 AM UTC-4, Phil Hobbs wrote:
On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

I bought DN2540's -1.5 to -3.5V.. but that's no different than the
lnd150's spread. Have you measured any?

All the LND150s I've seen were right around 1.6 mA I_DSS. If the
DN2530s are the same way, we can probably use them for our own products,
but not in designs for licensing or work-for-hire.

The On Semi NSIC2020JB is 20 mA +- 15%, and has a small signal
resistance of around 35 ohms at room temperature. For input protection
on a high-Z input, it would contribute only about 0.76 nV 1-Hz noise at
300 K, and I could use low-capacitance Schottkys to the supply rails
with no worries.

Hmmm if I get a batch of lnd150's with closer to -3V than whatever
I'm seeing now that could be a problem.

I'll have to measure some... I'm mostly machining today. I found this
2-56 gun tap in our drawer. It's really slick, shoots the chip out the
far end of the hole, rather than having to work the tap in and out.
(Wouldn't be so good for a blind tapped hole though.)

Fun.

Cheers

Phil Hobbs
(doing Gerbers and proposals today--less fun)


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

On Thursday, May 31, 2018 at 4:34:40 PM UTC-4, Phil Hobbs wrote:

On 05/31/2018 01:12 PM, George Herold wrote:
On Thursday, May 31, 2018 at 10:45:04 AM UTC-4, Phil Hobbs wrote:
On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

I bought DN2540's -1.5 to -3.5V.. but that's no different than the
lnd150's spread. Have you measured any?

All the LND150s I've seen were right around 1.6 mA I_DSS. If the
DN2530s are the same way, we can probably use them for our own products,
but not in designs for licensing or work-for-hire.

The On Semi NSIC2020JB is 20 mA +- 15%, and has a small signal
resistance of around 35 ohms at room temperature. For input protection
on a high-Z input, it would contribute only about 0.76 nV 1-Hz noise at
300 K, and I could use low-capacitance Schottkys to the supply rails
with no worries.


Hmmm if I get a batch of lnd150's with closer to -3V than whatever
I'm seeing now that could be a problem.

I'll have to measure some... I'm mostly machining today. I found this
2-56 gun tap in our drawer. It's really slick, shoots the chip out the
far end of the hole, rather than having to work the tap in and out.
(Wouldn't be so good for a blind tapped hole though.)


Fun.

Yeah, I don't get to do it much these days, but I enjoy machining.
(turning a hunk of metal into something useful.)

Cheers

Phil Hobbs
(doing Gerbers and proposals today--less fun)

Sorry, there's always scut work, not sure how to classify
proposals. Someone's gotta pay the bills.

George H.

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Thu, 31 May 2018 10:44:53 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

Do you find that it's consistent enough in real life to make a good
current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks
like about 35 ohms at room temperature, which wouldn't be bad for input
protection of lowish-noise amps.

Cheers

Phil Hobbs

I haven't tested enough of the DN2530s to get statistics. But all of
the LND250s that I've tried had Idss close to 1.6 mA. The spec is 1 to
3.

What's that ON part number?


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Friday, June 1, 2018 at 9:17:41 AM UTC-4, John Larkin wrote:

On Thu, 31 May 2018 10:44:53 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

Do you find that it's consistent enough in real life to make a good
current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks
like about 35 ohms at room temperature, which wouldn't be bad for input
protection of lowish-noise amps.

Cheers

Phil Hobbs

I haven't tested enough of the DN2530s to get statistics. But all of
the LND250s that I've tried had Idss close to 1.6 mA. The spec is 1 to
3.

What's that ON part number?

This one I think
http://www.onsemi.com/pub/Collateral/NSIC2020JB-D.PDF

GH

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Phil Hobbs]

On 06/01/18 09:17, John Larkin wrote:

On Thu, 31 May 2018 10:44:53 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

Do you find that it's consistent enough in real life to make a good
current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks
like about 35 ohms at room temperature, which wouldn't be bad for input
protection of lowish-noise amps.

Cheers

Phil Hobbs

I haven't tested enough of the DN2530s to get statistics. But all of
the LND250s that I've tried had Idss close to 1.6 mA. The spec is 1 to
3.

What's that ON part number?

NSI45030AZT1G is 30 mA +- 15%, 45V, and
NSIC2020JBT3G is 20 mA +- 15%, 120V. They have lots of others.

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

 

[John Larkin]

On Fri, 1 Jun 2018 16:36:01 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 06/01/18 09:17, John Larkin wrote:
On Thu, 31 May 2018 10:44:53 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

Do you find that it's consistent enough in real life to make a good
current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks
like about 35 ohms at room temperature, which wouldn't be bad for input
protection of lowish-noise amps.

Cheers

Phil Hobbs

I haven't tested enough of the DN2530s to get statistics. But all of
the LND250s that I've tried had Idss close to 1.6 mA. The spec is 1 to
3.

What's that ON part number?



NSI45030AZT1G is 30 mA +- 15%, 45V, and

Oh, the 2-terminal ones. I have some of those. Probably depletion
mosfets. Ohmic near zero volts, with a reverse substrate diode.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Hobbs]

On 06/01/18 20:47, John Larkin wrote:

On Fri, 1 Jun 2018 16:36:01 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 06/01/18 09:17, John Larkin wrote:
On Thu, 31 May 2018 10:44:53 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 07:59 PM, John Larkin wrote:
On Wed, 30 May 2018 12:09:32 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/30/2018 11:23 AM, John Larkin wrote:
https://www.diodes.com/assets/Datasheets/AL5890.pdf

The block diagram shows this as a closed-loop regulator, not just some
jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its
use, but it is cute.

Fun. Might be a good safety feature for George's APD supply if it's
quick enough. It's hard to get into much trouble with 10 mA, and that's
way more than an APD needs. Mine uses LND150 depletion MOSFETs because
I want a lower current limit.

Cheers

Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.



I bought a bunch of depletion MOSFETs recently, including some of those.
Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and
there's only a minimum for transconductance and a maximum I_DSS.

Do you find that it's consistent enough in real life to make a good
current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks
like about 35 ohms at room temperature, which wouldn't be bad for input
protection of lowish-noise amps.

Cheers

Phil Hobbs

I haven't tested enough of the DN2530s to get statistics. But all of
the LND250s that I've tried had Idss close to 1.6 mA. The spec is 1 to
3.

What's that ON part number?



NSI45030AZT1G is 30 mA +- 15%, 45V, and

Oh, the 2-terminal ones. I have some of those. Probably depletion
mosfets. Ohmic near zero volts, with a reverse substrate diode.

Roight. The 3-terminal ones don't seem to be as good--at 0.5V D-S
they're only up to 14% of max current, whereas the two-terminal ones are
about 45%. So maybe they have resistors in both gate and source, and
the external resistor is in parallel with the gate resistor.

S D
0-----*-RRRR-*----*-* ,---------0
| | | V |
| R -------
| R ,-----
| R |
| | |
`-RRRR-*---*
|
0
Rx

Except that the current limit actually goes up when you put in the
resistor, whereas in the circuit above it goes down.

Wonder what the actual circuit looks like.

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