Forums

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

Started by Mike Randelzhofer November 2, 2022
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
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