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 guessOK, live dangerously, an NPN and one resistor. Or a dual diode and one resistor. Just barely, one transistor and no resistors.
Idea for a simple -1.5V 20mA power supply?
Started by ●November 2, 2022
Reply by ●November 2, 20222022-11-02
Reply by ●November 2, 20222022-11-02
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
Reply by ●November 2, 20222022-11-02
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
Reply by ●November 2, 20222022-11-02
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
Reply by ●November 2, 20222022-11-02
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.
Reply by ●November 3, 20222022-11-03
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
Reply by ●November 3, 20222022-11-03
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)
Reply by ●November 3, 20222022-11-03
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
Reply by ●November 3, 20222022-11-03
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
Reply by ●November 3, 20222022-11-03
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.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
