Idea for a simple -1.5V 20mA power supply?...

  • Thread starter Mike Randelzhofer
  • Start date
On 02/11/2022 17:53, Mike Randelzhofer wrote:
As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.
Click to expand...

Depends how much you can take from the FPGA outputs without annoying
them but drive a pair with antiphase square waves AC coupled to a diode
doubler using low drop diode won\'t be too far off LED drive voltage.

--
Regards,
Martin Brown
 
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs
Click to expand...

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.
 
John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.
Click to expand...

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 Thu, 3 Nov 2022 16:41:02 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.

Cheers

Phil Hobbs
Click to expand...

Where is the second one?
 
John Larkin wrote:
On Thu, 3 Nov 2022 16:41:02 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.

Cheers

Phil Hobbs

Where is the second one?
Click to expand...

IIRC the idea was to drive a LED from logic with a BJT and one resistor.

You FPGA-savvy folks may think of +0.9V as a logic high, but those of us
still in the 3.3- or 5-V trailing edge of technology aren\'t there yet. ;)

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 Thu, 3 Nov 2022 20:57:08 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 3 Nov 2022 16:41:02 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.

Cheers

Phil Hobbs

Where is the second one?


IIRC the idea was to drive a LED from logic with a BJT and one resistor.

You FPGA-savvy folks may think of +0.9V as a logic high, but those of us
still in the 3.3- or 5-V trailing edge of technology aren\'t there yet. ;)

Cheers

Phil Hobbs
Click to expand...

I thought this is what he wanted to do.

https://www.dropbox.com/s/ydlr0z8hdgc5x06/LED_0.9V.jpg?raw=1

Maybe not.
 
fredag den 4. november 2022 kl. 01.57.17 UTC+1 skrev Phil Hobbs:
John Larkin wrote:
On Thu, 3 Nov 2022 16:41:02 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.

Cheers

Phil Hobbs

Where is the second one?

IIRC the idea was to drive a LED from logic with a BJT and one resistor.
Click to expand...

as I understood it the idea was to turn on an LED when a 0.9V power rail is present
 
John Larkin wrote:
On Thu, 3 Nov 2022 20:57:08 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 3 Nov 2022 16:41:02 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.

Cheers

Phil Hobbs

Where is the second one?


IIRC the idea was to drive a LED from logic with a BJT and one resistor.

You FPGA-savvy folks may think of +0.9V as a logic high, but those of us
still in the 3.3- or 5-V trailing edge of technology aren\'t there yet. ;)

Cheers

Phil Hobbs

I thought this is what he wanted to do.

https://www.dropbox.com/s/ydlr0z8hdgc5x06/LED_0.9V.jpg?raw=1

Maybe not.


Right, the OP. There\'s that. ;)
Click to expand...

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 Fri, 4 Nov 2022 09:59:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 3 Nov 2022 20:57:08 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 3 Nov 2022 16:41:02 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.

Cheers

Phil Hobbs

Where is the second one?


IIRC the idea was to drive a LED from logic with a BJT and one resistor.

You FPGA-savvy folks may think of +0.9V as a logic high, but those of us
still in the 3.3- or 5-V trailing edge of technology aren\'t there yet. ;)

Cheers

Phil Hobbs

I thought this is what he wanted to do.

https://www.dropbox.com/s/ydlr0z8hdgc5x06/LED_0.9V.jpg?raw=1

Maybe not.


Right, the OP. There\'s that. ;)

Cheers

Phil Hobbs
Click to expand...

We leave OPs in the dust.
 
Am 04.11.2022 um 08:56 schrieb Lasse Langwadt Christensen:
fredag den 4. november 2022 kl. 01.57.17 UTC+1 skrev Phil Hobbs:
John Larkin wrote:
On Thu, 3 Nov 2022 16:41:02 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 23:10:11 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 20:12:46 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 2 Nov 2022 14:42:45 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

onsdag den 2. november 2022 kl. 22.23.01 UTC+1 skrev John Larkin:
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
m...@oho-elektronik.de> wrote:

As asked in the header, does anybody have an idea for simply generating
a low negative voltage for indicator leds on low output voltages e.g.
0.9V on FPGA core supplies ?

Non-red leds (green, yellow, white) need at least 2V or more so a direct
connection to low voltage regulators for indicating presence doesn\'t
make sense.

Of course a driving NPN could be used however on many voltage outputs a
negative supply would be an alternative.

Using some kind of phase output of buck regulators is one of the
possibilities, is there any other simpler idea ?

Thanks for all suggestions,
Mike


Doesn\'t the FPGA have higher power bank voltages?

A simple flyback booster would work.

yes, thats an idea, but how many parts does it cost ?

I\'d like to have a voltage that doesn\'t light a led when the vreg output
is 0 or GND.

An ICL7660 with regulated output voltage of 1.5 or 1.23V would be perfect.

These old 7660 are quite pricey ...
https://www.digikey.de/de/products/detail/renesas-electronics-america-inc/ICL7660AIBAZA-T/1034510

Thanks,
Mike

Is any higher voltage available to run the LED? FPGA core voltages are
usually switched down from something else.

No answer, can\'t help.



sorry, 3.3V are available...
OK, why not an NPN transistor and two resistors?

not enough Rube Goldberg I guess

OK, live dangerously, an NPN and one resistor.

It\'s okay if it\'s an emitter follower.

How about a resistor in the emitter, to make it a (mostly) controlled
current sink?

Unless Rbb\' is fairly huge, the BJT will saturate massively and all the
current will come in via the base. A prebiased transistor and a
collector resistor would work.

Cheers

Phil Hobbs

+0.9 to base, 0.65 Vbe drop, 0.25 across a 250 ohm emitter resistor to
ground, 1 mA collector current through the LED, microamps of base
current.

Sure, but that takes two resistors.

Cheers

Phil Hobbs

Where is the second one?

IIRC the idea was to drive a LED from logic with a BJT and one resistor.

as I understood it the idea was to turn on an LED when a 0.9V power rail is present
Click to expand...

The original thought was exactly that, want a simple supply supervisor,
a supervisor MCU can measure exactly but a quick view whats happening is
always desirable - but if the cost of the led circuitry is a transistor,
its IMHO a doubtful solution.

But the current source idea is nice because it shows small changes in
voltage on the led.
It also could be used to show IO pin states, another interesting
application.

The original intent was to have a small negative supply which also could
be useful in some analog circuitry.

Thanks for all ideas,
Mike


--
Mike Randelzhofer, OHO-Elektronik
 
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