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

  • Thread starter Mike Randelzhofer
  • Start date
M

Mike Randelzhofer

Guest
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


--
Mike Randelzhofer, OHO-Elektronik
 
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
<mr@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.
 
Am 02.11.2022 um 19:04 schrieb John Larkin:
On Wed, 2 Nov 2022 18:53:06 +0100, Mike Randelzhofer
mr@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


--
Mike Randelzhofer, OHO-Elektronik
 
I would look into switch capacitor circuits but I\'m not sure I like the idea at all. You want to tie the cathode of the LED through a resistor to -1.5v. When the signal at 0.9v, you have 2.4 volts across the LED and it turns on. When the signal is at 0V, the LED has less than it\'s ON voltage, so it\'s off and you\'re hoping that the leakage current with 1.5v across the LED isn\'t high enough to pull the pin below ground enough to damage some ultra-low power 0.9v device. I would rethink that plan.
 
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
<mr@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
mr@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.

If you do have some voltage to run the LED, all you need is a
comparator (or an NPN transistor) to detect that the core voltage is
there.
 
Am 02.11.2022 um 04:08 schrieb Wanderer@noplace.com:
> I would look into switch capacitor circuits but I\'m not sure I like the idea at all. You want to tie the cathode of the LED through a resistor to -1.5v. When the signal at 0.9v, you have 2.4 volts across the LED and it turns on. When the signal is at 0V, the LED has less than it\'s ON voltage, so it\'s off and you\'re hoping that the leakage current with 1.5v across the LED isn\'t high enough to pull the pin below ground enough to damage some ultra-low power 0.9v device. I would rethink that plan.

yeah good point, its an issue to discuss.

The low current leds should have a resistor as well and the current
should be about 1mA or below.
Modern leds are very bright these days...

And the negative voltage @1.2V or so should not damage an IO pin when
current is in the uA range.

Its probably a bad idea because of the high effort to generate a
regulated -1.2V.
This voltage could be clamped by an IR diode though ?

Thinking about basic design ideas to not get into politics...

Thanks,
Mike

--
Mike Randelzhofer, OHO-Elektronik
 
Am 02.11.2022 um 21:14 schrieb John Larkin:
On Wed, 2 Nov 2022 20:43:08 +0100, Mike Randelzhofer
mr@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
mr@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.

If you do have some voltage to run the LED, all you need is a
comparator (or an NPN transistor) to detect that the core voltage is
there.

yes, some designs use transistors to detect voltage (could also use RET
- resistor equipped transistors) but i like the direct approach.

To drive a low current led with a transistor is like using an i9-13900k
for a led blinker :)

Thanks,
Mike

--
Mike Randelzhofer, OHO-Elektronik
 
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
<mr@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
mr@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
mr@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.




If you do have some voltage to run the LED, all you need is a
comparator (or an NPN transistor) to detect that the core voltage is
there.


yes, some designs use transistors to detect voltage (could also use RET
- resistor equipped transistors) but i like the direct approach.

To drive a low current led with a transistor is like using an i9-13900k
for a led blinker :)

Thanks,
Mike
 
Am 02.11.2022 um 21:54 schrieb John Larkin:
On Wed, 2 Nov 2022 21:25:17 +0100, Mike Randelzhofer
mr@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
mr@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
mr@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...

--
Mike Randelzhofer, OHO-Elektronik
 
On Wed, 2 Nov 2022 22:18:34 +0100, Mike Randelzhofer
<mr@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
mr@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
mr@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
mr@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?
 
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
 
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.

Or a dual diode and one resistor.

Just barely, one transistor and no resistors.
 
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.

Or a dual diode and one resistor.

Just barely, one transistor and no resistors.

Or just a LED and a battery. A zillion Chinesium flashlights can\'t be
wrong, surely?

Cheers

Phil Hobbs
 
torsdag den 3. november 2022 kl. 01.12.53 UTC+1 skrev Phil Hobbs:
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.

3.3V might be just enough for \"constant\" current sink with a emitter resistor
 
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?


Or a dual diode and one resistor.

Just barely, one transistor and no resistors.

Or just a LED and a battery. A zillion Chinesium flashlights can\'t be
wrong, surely?

Cheers

Phil Hobbs
 
On Wed, 2 Nov 2022 17:26:09 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

torsdag den 3. november 2022 kl. 01.12.53 UTC+1 skrev Phil Hobbs:
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.

3.3V might be just enough for \"constant\" current sink with a emitter resistor

Yes, that\'s one way to do it.

Or offend a lot of people and ground the emitter and beta limit. With
a beta binned part, like BCX71K or something, that\'s actually not
awful.
 
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

--
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 Wednesday, November 2, 2022 at 8:10:20 PM UTC-7, Phil Hobbs 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 ?

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

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

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?

Yep, that\'s a good plan; LED from +3.3V to collector.

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.

Emitter resistance doesn\'t allow much base bias (i.e. base current)
when the transistor ISN\"T yet saturated, and... it\'ll never really saturate
if the I*R_emitter + Vbe = 0.9V condition is scaled right. You do want, though,
the LED to glow with less than 3.3 -Vce(sat) ~=3V (can\'t do it with a blue LED on 3.3V)
 
On 02/11/2022 8:19 pm, Mike Randelzhofer wrote:
Am 02.11.2022 um 04:08 schrieb Wanderer@noplace.com:
I would look into switch capacitor circuits but I\'m not sure I like
the idea at all. You want to tie the cathode of the LED through a
resistor to -1.5v. When the signal at 0.9v, you have 2.4 volts across
the LED and it turns on. When the signal is at 0V, the LED has less
than it\'s ON voltage, so it\'s off and you\'re hoping that the leakage
current with 1.5v across the LED isn\'t high enough to pull the pin
below ground enough to damage some ultra-low power 0.9v device. I
would rethink that plan.

yeah good point, its an issue to discuss.

The low current leds should have a resistor as well and the current
should be about 1mA or below.
Modern leds are very bright these days...

And the negative voltage @1.2V or so should not damage an IO pin when
current is in the uA range.

Its probably a bad idea because of the high effort to generate a
regulated -1.2V.
This voltage could be clamped by an IR diode though ?

Thinking about basic design ideas to not get into politics...

Thanks,
Mike

Very minimalist would be to drive the LEDs from a +2.5V or 3.3V rail and
choose highish series resistor so the eye discerns the brightness change
between 0V and 0.9V - for comparison include two extra LEDs in the
bunch, one at 0V, one at 0.9V to serve as brightness references for the eye?

piglet
 
On Wednesday, November 2, 2022 at 1:53:22 PM UTC-4, 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.

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 ?

LEDs are not used to detect voltage thresholds, there\'s not enough precision, they are mainly indicators.

There are vast numbers of micropower precision voltage detectors with built-in voltage references that can be used for this application. Many of them cost only slightly more than a dime in quantity. You can use a part like this to turn a LED ON and OFF directly. And they run off any number of power supply voltages commonly seen in digital designs, no negative supply needed.

Even these are under $0.50 in unit quantity, they\'re old:

https://www.diodes.com/about/news/press-releases/micro-power-voltage-detector-from-diodes-incorporated-monitors-power-supplies-in-computers-and-digital-systems/

Look around their whole line to find what fits.

Thanks for all suggestions,
Mike


--
Mike Randelzhofer, OHO-Elektronik
 

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