Forums

Zener diode below-threshold reverse current

Started by Tim Wescott June 23, 2016
On Wed, 27 Jul 2016 21:34:19 -0500, John Fields
<jfields@austininstruments.com> wrote:

>On Wed, 27 Jul 2016 14:57:59 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>On Wed, 27 Jul 2016 14:49:40 -0500, John Fields >><jfields@austininstruments.com> wrote: >> >>>On Sun, 10 Jul 2016 17:58:29 -0400, krw@attt.bizz wrote: >>> >>>>On Sun, 10 Jul 2016 16:01:50 -0500, John Fields >>>><jfields@austininstruments.com> wrote: >>>> >>>>>On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> wrote: >>>>> >>>>>>On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott <tim@seemywebsite.com> >>>>>>wrote: >>>>>> >>>>>>>On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson wrote: >>>>>>> >>>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott >>>>>>>> <seemywebsite@myfooter.really> wrote: >>>>>>>> >>>>>>>>>I know the theory, more or less. >>>>>>>>> >>>>>>>>>In practice, what's the reverse current through a zener diode at levels >>>>>>>>>well below the breakdown voltage? I've got a circuit where I'm feeding >>>>>>>>>a 12V linear regulator with a 25V line. It would be handy to put a >>>>>>>>>zener diode in there so that when the 25V line drops to 4V the current >>>>>>>>>into the regulator drops to tens of microamps. I'm wondering if a >>>>>>>>>series zener will do it. >>>>>>>> >>>>>>>> Clear as mud ;-) Post a schematic of what you mean... 25V -> 4V ?? >>>>>>>> >>>>>>>> ...Jim Thompson >>>>>>> >>>>>>>Sorry. When the circuit is nominally on I want to make 12V from the 25V >>>>>>>rail with a linear regulator. When the circuit is nominally off the 25V >>>>>>>rail is at 4V, and I would like to effectively shut off the 12V line >>>>>>>entirely. >>>>>>> >>>>>>>A 6.8V zener would make for around 18V at the input to the regulator, so >>>>>>>the "on" part works fine. I'm just wondering if, with 4V on one side and >>>>>>>a regulator input on the other, if the zener will flow some predictably >>>>>>>low current. >>>>>> >>>>>>6.8V zeners suck. I'd just use an enable pin on the regulator. >>>>> >>>>>And if the regulator of choice has no ENABLE pin, then what? >>>> >>>>Then choose another, asshole. >>> >>>--- >>>That's no help, since hostility leads, reductio ad absurdum, to war. >>> >>>Do you want to declare war with your limited resources? >>>--- >>> >>>>When you want to discuss electronics, let us all know. >>> >>>--- >>>I'm always up for that, but your invitation is preumptuous, as if you >>>were running the game. >>> >>>JF >> >>That's silly. I'm running the game. > >--- >Then you create unhappiness because you wallow in it? > >JF
I create electronics because people need it. We just solved a problem with thrust measurement in a GTF. Things like that are satisfying. What do you do? -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 7/27/2016 3:00 PM, rickman wrote:
> On 7/27/2016 3:05 PM, John Fields wrote: >> On Sun, 10 Jul 2016 17:15:51 -0400, rickman <gnuarm@gmail.com> wrote: >> >>> On 7/10/2016 5:01 PM, John Fields wrote: >>>> On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> wrote: >>>> >>>>> On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott <tim@seemywebsite.com> >>>>> wrote: >>>>> >>>>>> On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson wrote: >>>>>> >>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott >>>>>>> <seemywebsite@myfooter.really> wrote: >>>>>>> >>>>>>>> I know the theory, more or less. >>>>>>>> >>>>>>>> In practice, what's the reverse current through a zener diode at >>>>>>>> levels >>>>>>>> well below the breakdown voltage? I've got a circuit where I'm >>>>>>>> feeding >>>>>>>> a 12V linear regulator with a 25V line. It would be handy to put a >>>>>>>> zener diode in there so that when the 25V line drops to 4V the >>>>>>>> current >>>>>>>> into the regulator drops to tens of microamps. I'm wondering if a >>>>>>>> series zener will do it. >>>>>>> >>>>>>> Clear as mud ;-) Post a schematic of what you mean... 25V -> 4V ?? >>>>>>> >>>>>>> ...Jim Thompson >>>>>> >>>>>> Sorry. When the circuit is nominally on I want to make 12V from >>>>>> the 25V >>>>>> rail with a linear regulator. When the circuit is nominally off >>>>>> the 25V >>>>>> rail is at 4V, and I would like to effectively shut off the 12V line >>>>>> entirely. >>>>>> >>>>>> A 6.8V zener would make for around 18V at the input to the >>>>>> regulator, so >>>>>> the "on" part works fine. I'm just wondering if, with 4V on one >>>>>> side and >>>>>> a regulator input on the other, if the zener will flow some >>>>>> predictably >>>>>> low current. >>>>> >>>>> 6.8V zeners suck. I'd just use an enable pin on the regulator. >> >> --- >> Actually, raw 6.8 volt Zeners pretty much rule in terms of voltage >> tempco, so they don't suck as much as you claim. >> --- >> >>>> And if the regulator of choice has no ENABLE pin, then what? >>> >>> Then "choise" another regulator... There is no shortage of suitable >>> regulators in spite of the inability of some people to find them. >> >> --- >> "Choise"??? >> --- >> >>>>> Some have an accurate reference so you can program the dropout >>>>> voltage with >>>>> just a voltage divider. When the input drops below that value, the >>>>> regulator shuts off (see: UVLO - Under Voltage Lock Out). >>>> >>>> --- >>>> Wescott was obviously referring to a three terminal series regulator, >>>> so your rsponse is irrelevant. >>>> >>>> As to your damnation of 6.8 volt Zeners, 6.8 volts is pretty close to >>>> where, with the specified reverse current through the diode, the >>>> Zener's tempco goes away, so why would you think 6.8 volt Zeners suck? >>> >>> If someone wants to limit themselves to unsuitable regulators, then it >>> can be hard to help them with electronics design. Tim is willing to >>> consider regulators with an enable, but he can't see to get past the >>> limitations of the Digikey selection tool. I recommend starting with >>> the TI tool on their web site. It's easier to find a part on their site >>> that meets the requirements. >> >> Rather than damning one tool and blessing another, wouldn't it be >> better to teach a man how to fish? > > I had fish last night...
Were they polite guests?
On Wednesday, July 27, 2016 at 10:56:08 PM UTC-4, rickman wrote:
> On 7/27/2016 10:38 PM, John Fields wrote: > > On Wed, 27 Jul 2016 16:00:57 -0400, rickman <gnuarm@gmail.com> wrote: > > > >> On 7/27/2016 3:05 PM, John Fields wrote: > >>> On Sun, 10 Jul 2016 17:15:51 -0400, rickman <gnuarm@gmail.com> wrote: > >>> > >>>> On 7/10/2016 5:01 PM, John Fields wrote: > >>>>> On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> wrote: > >>>>> > >>>>>> On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott <tim@seemywebsite.com> > >>>>>> wrote: > >>>>>> > >>>>>>> On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson wrote: > >>>>>>> > >>>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott > >>>>>>>> <seemywebsite@myfooter.really> wrote: > >>>>>>>> > >>>>>>>>> I know the theory, more or less. > >>>>>>>>> > >>>>>>>>> In practice, what's the reverse current through a zener diode at levels > >>>>>>>>> well below the breakdown voltage? I've got a circuit where I'm feeding > >>>>>>>>> a 12V linear regulator with a 25V line. It would be handy to put a > >>>>>>>>> zener diode in there so that when the 25V line drops to 4V the current > >>>>>>>>> into the regulator drops to tens of microamps. I'm wondering if a > >>>>>>>>> series zener will do it. > >>>>>>>> > >>>>>>>> Clear as mud ;-) Post a schematic of what you mean... 25V -> 4V ?? > >>>>>>>> > >>>>>>>> ...Jim Thompson > >>>>>>> > >>>>>>> Sorry. When the circuit is nominally on I want to make 12V from the 25V > >>>>>>> rail with a linear regulator. When the circuit is nominally off the 25V > >>>>>>> rail is at 4V, and I would like to effectively shut off the 12V line > >>>>>>> entirely. > >>>>>>> > >>>>>>> A 6.8V zener would make for around 18V at the input to the regulator, so > >>>>>>> the "on" part works fine. I'm just wondering if, with 4V on one side and > >>>>>>> a regulator input on the other, if the zener will flow some predictably > >>>>>>> low current. > >>>>>> > >>>>>> 6.8V zeners suck. I'd just use an enable pin on the regulator. > >>> > >>> --- > >>> Actually, raw 6.8 volt Zeners pretty much rule in terms of voltage > >>> tempco, so they don't suck as much as you claim. > >>> --- > >>> > >>>>> And if the regulator of choice has no ENABLE pin, then what? > >>>> > >>>> Then "choise" another regulator... There is no shortage of suitable > >>>> regulators in spite of the inability of some people to find them. > >>> > >>> --- > >>> "Choise"??? > >>> --- > >>> > >>>>>> Some have an accurate reference so you can program the dropout voltage with > >>>>>> just a voltage divider. When the input drops below that value, the > >>>>>> regulator shuts off (see: UVLO - Under Voltage Lock Out). > >>>>> > >>>>> --- > >>>>> Wescott was obviously referring to a three terminal series regulator, > >>>>> so your rsponse is irrelevant. > >>>>> > >>>>> As to your damnation of 6.8 volt Zeners, 6.8 volts is pretty close to > >>>>> where, with the specified reverse current through the diode, the > >>>>> Zener's tempco goes away, so why would you think 6.8 volt Zeners suck? > >>>> > >>>> If someone wants to limit themselves to unsuitable regulators, then it > >>>> can be hard to help them with electronics design. Tim is willing to > >>>> consider regulators with an enable, but he can't see to get past the > >>>> limitations of the Digikey selection tool. I recommend starting with > >>>> the TI tool on their web site. It's easier to find a part on their site > >>>> that meets the requirements. > >>> > >>> Rather than damning one tool and blessing another, wouldn't it be > >>> better to teach a man how to fish? > >> > >> I had fish last night... > > > > --- > > Which, no doubt, was stepped on three or four times before it got to > > your table, so you don't know how to fish, you know how to buy. > > I know how to fish. I don't know how to keep turtles from swallowing my > hook, so I don't fish. Hell, I live on a lake. But like most places it > is not recommended that you eat the fish too often.
How the f--- does a turtle bite your bait unless you're fishing for some filthy bottom feeder. Try using something called a "bobber."
> > -- > > Rick C
On Thu, 28 Jul 2016 10:37:18 -0700 (PDT) bloggs.fredbloggs.fred@gmail.com
wrote in Message id:
<4bf2b72b-5dea-4309-9686-4b50f7e82562@googlegroups.com>:

>On Wednesday, July 27, 2016 at 10:56:08 PM UTC-4, rickman wrote: >> On 7/27/2016 10:38 PM, John Fields wrote: >> > On Wed, 27 Jul 2016 16:00:57 -0400, rickman <gnuarm@gmail.com> wrote: >> > >> >> On 7/27/2016 3:05 PM, John Fields wrote: >> >>> On Sun, 10 Jul 2016 17:15:51 -0400, rickman <gnuarm@gmail.com> wrote: >> >>> >> >>>> On 7/10/2016 5:01 PM, John Fields wrote: >> >>>>> On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> wrote: >> >>>>> >> >>>>>> On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott <tim@seemywebsite.com> >> >>>>>> wrote: >> >>>>>> >> >>>>>>> On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson wrote: >> >>>>>>> >> >>>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott >> >>>>>>>> <seemywebsite@myfooter.really> wrote: >> >>>>>>>> >> >>>>>>>>> I know the theory, more or less. >> >>>>>>>>> >> >>>>>>>>> In practice, what's the reverse current through a zener diode at levels >> >>>>>>>>> well below the breakdown voltage? I've got a circuit where I'm feeding >> >>>>>>>>> a 12V linear regulator with a 25V line. It would be handy to put a >> >>>>>>>>> zener diode in there so that when the 25V line drops to 4V the current >> >>>>>>>>> into the regulator drops to tens of microamps. I'm wondering if a >> >>>>>>>>> series zener will do it. >> >>>>>>>> >> >>>>>>>> Clear as mud ;-) Post a schematic of what you mean... 25V -> 4V ?? >> >>>>>>>> >> >>>>>>>> ...Jim Thompson >> >>>>>>> >> >>>>>>> Sorry. When the circuit is nominally on I want to make 12V from the 25V >> >>>>>>> rail with a linear regulator. When the circuit is nominally off the 25V >> >>>>>>> rail is at 4V, and I would like to effectively shut off the 12V line >> >>>>>>> entirely. >> >>>>>>> >> >>>>>>> A 6.8V zener would make for around 18V at the input to the regulator, so >> >>>>>>> the "on" part works fine. I'm just wondering if, with 4V on one side and >> >>>>>>> a regulator input on the other, if the zener will flow some predictably >> >>>>>>> low current. >> >>>>>> >> >>>>>> 6.8V zeners suck. I'd just use an enable pin on the regulator. >> >>> >> >>> --- >> >>> Actually, raw 6.8 volt Zeners pretty much rule in terms of voltage >> >>> tempco, so they don't suck as much as you claim. >> >>> --- >> >>> >> >>>>> And if the regulator of choice has no ENABLE pin, then what? >> >>>> >> >>>> Then "choise" another regulator... There is no shortage of suitable >> >>>> regulators in spite of the inability of some people to find them. >> >>> >> >>> --- >> >>> "Choise"??? >> >>> --- >> >>> >> >>>>>> Some have an accurate reference so you can program the dropout voltage with >> >>>>>> just a voltage divider. When the input drops below that value, the >> >>>>>> regulator shuts off (see: UVLO - Under Voltage Lock Out). >> >>>>> >> >>>>> --- >> >>>>> Wescott was obviously referring to a three terminal series regulator, >> >>>>> so your rsponse is irrelevant. >> >>>>> >> >>>>> As to your damnation of 6.8 volt Zeners, 6.8 volts is pretty close to >> >>>>> where, with the specified reverse current through the diode, the >> >>>>> Zener's tempco goes away, so why would you think 6.8 volt Zeners suck? >> >>>> >> >>>> If someone wants to limit themselves to unsuitable regulators, then it >> >>>> can be hard to help them with electronics design. Tim is willing to >> >>>> consider regulators with an enable, but he can't see to get past the >> >>>> limitations of the Digikey selection tool. I recommend starting with >> >>>> the TI tool on their web site. It's easier to find a part on their site >> >>>> that meets the requirements. >> >>> >> >>> Rather than damning one tool and blessing another, wouldn't it be >> >>> better to teach a man how to fish? >> >> >> >> I had fish last night... >> > >> > --- >> > Which, no doubt, was stepped on three or four times before it got to >> > your table, so you don't know how to fish, you know how to buy. >> >> I know how to fish. I don't know how to keep turtles from swallowing my >> hook, so I don't fish. Hell, I live on a lake. But like most places it >> is not recommended that you eat the fish too often. > >How the f--- does a turtle bite your bait unless you're fishing for some filthy bottom feeder. Try using something called a "bobber."
Try telling that to a trout fisherman. Bobbers are for kids, you amateur.
On Thu, 28 Jul 2016 14:32:00 -0400, JW <none@dev.null> wrote:

>On Thu, 28 Jul 2016 10:37:18 -0700 (PDT) bloggs.fredbloggs.fred@gmail.com >wrote in Message id: ><4bf2b72b-5dea-4309-9686-4b50f7e82562@googlegroups.com>: > >>On Wednesday, July 27, 2016 at 10:56:08 PM UTC-4, rickman wrote:
[snip]
>>> >>> I know how to fish. I don't know how to keep turtles from swallowing my >>> hook, so I don't fish. Hell, I live on a lake. But like most places it >>> is not recommended that you eat the fish too often. >> >>How the f--- does a turtle bite your bait unless you're fishing for some filthy bottom feeder. Try using something called a "bobber." > >Try telling that to a trout fisherman. Bobbers are for kids, you amateur.
Bloggs _is_ a bottom feeder, but rickman is a village idiot, so it's a toss-up ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website.
On 7/28/2016 12:37 PM, bloggs.fredbloggs.fred@gmail.com wrote:
> On Wednesday, July 27, 2016 at 10:56:08 PM UTC-4, rickman wrote: >> On 7/27/2016 10:38 PM, John Fields wrote: >>> On Wed, 27 Jul 2016 16:00:57 -0400, rickman <gnuarm@gmail.com> >>> wrote: >>> >>>> On 7/27/2016 3:05 PM, John Fields wrote: >>>>> On Sun, 10 Jul 2016 17:15:51 -0400, rickman >>>>> <gnuarm@gmail.com> wrote: >>>>> >>>>>> On 7/10/2016 5:01 PM, John Fields wrote: >>>>>>> On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> >>>>>>> wrote: >>>>>>> >>>>>>>> On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott >>>>>>>> <tim@seemywebsite.com> wrote: >>>>>>>> >>>>>>>>> On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott >>>>>>>>>> <seemywebsite@myfooter.really> wrote: >>>>>>>>>> >>>>>>>>>>> I know the theory, more or less. >>>>>>>>>>> >>>>>>>>>>> In practice, what's the reverse current through a >>>>>>>>>>> zener diode at levels well below the breakdown >>>>>>>>>>> voltage? I've got a circuit where I'm feeding a >>>>>>>>>>> 12V linear regulator with a 25V line. It would >>>>>>>>>>> be handy to put a zener diode in there so that >>>>>>>>>>> when the 25V line drops to 4V the current into >>>>>>>>>>> the regulator drops to tens of microamps. I'm >>>>>>>>>>> wondering if a series zener will do it. >>>>>>>>>> >>>>>>>>>> Clear as mud ;-) Post a schematic of what you >>>>>>>>>> mean... 25V -> 4V ?? ...Jim Thompson >>>>>>>>> >>>>>>>>> Sorry. When the circuit is nominally on I want to >>>>>>>>> make 12V from the 25V rail with a linear regulator. >>>>>>>>> When the circuit is nominally off the 25V rail is at >>>>>>>>> 4V, and I would like to effectively shut off the 12V >>>>>>>>> line entirely. >>>>>>>>> >>>>>>>>> A 6.8V zener would make for around 18V at the input >>>>>>>>> to the regulator, so the "on" part works fine. I'm >>>>>>>>> just wondering if, with 4V on one side and a >>>>>>>>> regulator input on the other, if the zener will flow >>>>>>>>> some predictably low current. >>>>>>>> >>>>>>>> 6.8V zeners suck. I'd just use an enable pin on the >>>>>>>> regulator. >>>>> >>>>> --- Actually, raw 6.8 volt Zeners pretty much rule in terms >>>>> of voltage tempco, so they don't suck as much as you claim. >>>>> --- >>>>> >>>>>>> And if the regulator of choice has no ENABLE pin, then >>>>>>> what? >>>>>> >>>>>> Then "choise" another regulator... There is no shortage of >>>>>> suitable regulators in spite of the inability of some >>>>>> people to find them. >>>>> >>>>> --- "Choise"??? --- >>>>> >>>>>>>> Some have an accurate reference so you can program the >>>>>>>> dropout voltage with just a voltage divider. When the >>>>>>>> input drops below that value, the regulator shuts off >>>>>>>> (see: UVLO - Under Voltage Lock Out). >>>>>>> >>>>>>> --- Wescott was obviously referring to a three terminal >>>>>>> series regulator, so your rsponse is irrelevant. >>>>>>> >>>>>>> As to your damnation of 6.8 volt Zeners, 6.8 volts is >>>>>>> pretty close to where, with the specified reverse current >>>>>>> through the diode, the Zener's tempco goes away, so why >>>>>>> would you think 6.8 volt Zeners suck? >>>>>> >>>>>> If someone wants to limit themselves to unsuitable >>>>>> regulators, then it can be hard to help them with >>>>>> electronics design. Tim is willing to consider regulators >>>>>> with an enable, but he can't see to get past the >>>>>> limitations of the Digikey selection tool. I recommend >>>>>> starting with the TI tool on their web site. It's easier >>>>>> to find a part on their site that meets the requirements. >>>>> >>>>> Rather than damning one tool and blessing another, wouldn't >>>>> it be better to teach a man how to fish? >>>> >>>> I had fish last night... >>> >>> --- Which, no doubt, was stepped on three or four times before it >>> got to your table, so you don't know how to fish, you know how to >>> buy. >> >> I know how to fish. I don't know how to keep turtles from >> swallowing my hook, so I don't fish. Hell, I live on a lake. But >> like most places it is not recommended that you eat the fish too >> often. > > How the f--- does a turtle bite your bait unless you're fishing for > some filthy bottom feeder. Try using something called a "bobber."
Oh, you mispelled "bobber" which should "Bloggser".
On Thursday, July 28, 2016 at 2:32:03 PM UTC-4, JW wrote:
> On Thu, 28 Jul 2016 10:37:18 -0700 (PDT) bloggs.fredbloggs.fred@gmail.com > wrote in Message id: > <4bf2b72b-5dea-4309-9686-4b50f7e82562@googlegroups.com>: > > >On Wednesday, July 27, 2016 at 10:56:08 PM UTC-4, rickman wrote: > >> On 7/27/2016 10:38 PM, John Fields wrote: > >> > On Wed, 27 Jul 2016 16:00:57 -0400, rickman <gnuarm@gmail.com> wrote: > >> > > >> >> On 7/27/2016 3:05 PM, John Fields wrote: > >> >>> On Sun, 10 Jul 2016 17:15:51 -0400, rickman <gnuarm@gmail.com> wrote: > >> >>> > >> >>>> On 7/10/2016 5:01 PM, John Fields wrote: > >> >>>>> On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> wrote: > >> >>>>> > >> >>>>>> On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott <tim@seemywebsite.com> > >> >>>>>> wrote: > >> >>>>>> > >> >>>>>>> On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson wrote: > >> >>>>>>> > >> >>>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott > >> >>>>>>>> <seemywebsite@myfooter.really> wrote: > >> >>>>>>>> > >> >>>>>>>>> I know the theory, more or less. > >> >>>>>>>>> > >> >>>>>>>>> In practice, what's the reverse current through a zener diode at levels > >> >>>>>>>>> well below the breakdown voltage? I've got a circuit where I'm feeding > >> >>>>>>>>> a 12V linear regulator with a 25V line. It would be handy to put a > >> >>>>>>>>> zener diode in there so that when the 25V line drops to 4V the current > >> >>>>>>>>> into the regulator drops to tens of microamps. I'm wondering if a > >> >>>>>>>>> series zener will do it. > >> >>>>>>>> > >> >>>>>>>> Clear as mud ;-) Post a schematic of what you mean... 25V -> 4V ?? > >> >>>>>>>> > >> >>>>>>>> ...Jim Thompson > >> >>>>>>> > >> >>>>>>> Sorry. When the circuit is nominally on I want to make 12V from the 25V > >> >>>>>>> rail with a linear regulator. When the circuit is nominally off the 25V > >> >>>>>>> rail is at 4V, and I would like to effectively shut off the 12V line > >> >>>>>>> entirely. > >> >>>>>>> > >> >>>>>>> A 6.8V zener would make for around 18V at the input to the regulator, so > >> >>>>>>> the "on" part works fine. I'm just wondering if, with 4V on one side and > >> >>>>>>> a regulator input on the other, if the zener will flow some predictably > >> >>>>>>> low current. > >> >>>>>> > >> >>>>>> 6.8V zeners suck. I'd just use an enable pin on the regulator. > >> >>> > >> >>> --- > >> >>> Actually, raw 6.8 volt Zeners pretty much rule in terms of voltage > >> >>> tempco, so they don't suck as much as you claim. > >> >>> --- > >> >>> > >> >>>>> And if the regulator of choice has no ENABLE pin, then what? > >> >>>> > >> >>>> Then "choise" another regulator... There is no shortage of suitable > >> >>>> regulators in spite of the inability of some people to find them. > >> >>> > >> >>> --- > >> >>> "Choise"??? > >> >>> --- > >> >>> > >> >>>>>> Some have an accurate reference so you can program the dropout voltage with > >> >>>>>> just a voltage divider. When the input drops below that value, the > >> >>>>>> regulator shuts off (see: UVLO - Under Voltage Lock Out). > >> >>>>> > >> >>>>> --- > >> >>>>> Wescott was obviously referring to a three terminal series regulator, > >> >>>>> so your rsponse is irrelevant. > >> >>>>> > >> >>>>> As to your damnation of 6.8 volt Zeners, 6.8 volts is pretty close to > >> >>>>> where, with the specified reverse current through the diode, the > >> >>>>> Zener's tempco goes away, so why would you think 6.8 volt Zeners suck? > >> >>>> > >> >>>> If someone wants to limit themselves to unsuitable regulators, then it > >> >>>> can be hard to help them with electronics design. Tim is willing to > >> >>>> consider regulators with an enable, but he can't see to get past the > >> >>>> limitations of the Digikey selection tool. I recommend starting with > >> >>>> the TI tool on their web site. It's easier to find a part on their site > >> >>>> that meets the requirements. > >> >>> > >> >>> Rather than damning one tool and blessing another, wouldn't it be > >> >>> better to teach a man how to fish? > >> >> > >> >> I had fish last night... > >> > > >> > --- > >> > Which, no doubt, was stepped on three or four times before it got to > >> > your table, so you don't know how to fish, you know how to buy. > >> > >> I know how to fish. I don't know how to keep turtles from swallowing my > >> hook, so I don't fish. Hell, I live on a lake. But like most places it > >> is not recommended that you eat the fish too often. > > > >How the f--- does a turtle bite your bait unless you're fishing for some filthy bottom feeder. Try using something called a "bobber." > > Try telling that to a trout fisherman. Bobbers are for kids, you amateur.
Looks to me like they in effect have a bobber with their hook assembly, it stays off the bottom by a distance determined by that weight thingamajig they crimp onto the line above the hook. However you slice it, it's not real complicated, Einstein.
On Wed, 27 Jul 2016 22:20:27 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On Wed, 27 Jul 2016 21:34:19 -0500, John Fields ><jfields@austininstruments.com> wrote: > >>On Wed, 27 Jul 2016 14:57:59 -0700, John Larkin >><jjlarkin@highlandtechnology.com> wrote: >> >>>On Wed, 27 Jul 2016 14:49:40 -0500, John Fields >>><jfields@austininstruments.com> wrote: >>> >>>>On Sun, 10 Jul 2016 17:58:29 -0400, krw@attt.bizz wrote: >>>> >>>>>On Sun, 10 Jul 2016 16:01:50 -0500, John Fields >>>>><jfields@austininstruments.com> wrote: >>>>> >>>>>>On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> wrote: >>>>>> >>>>>>>On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott <tim@seemywebsite.com> >>>>>>>wrote: >>>>>>> >>>>>>>>On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson wrote: >>>>>>>> >>>>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott >>>>>>>>> <seemywebsite@myfooter.really> wrote: >>>>>>>>> >>>>>>>>>>I know the theory, more or less. >>>>>>>>>> >>>>>>>>>>In practice, what's the reverse current through a zener diode at levels >>>>>>>>>>well below the breakdown voltage? I've got a circuit where I'm feeding >>>>>>>>>>a 12V linear regulator with a 25V line. It would be handy to put a >>>>>>>>>>zener diode in there so that when the 25V line drops to 4V the current >>>>>>>>>>into the regulator drops to tens of microamps. I'm wondering if a >>>>>>>>>>series zener will do it. >>>>>>>>> >>>>>>>>> Clear as mud ;-) Post a schematic of what you mean... 25V -> 4V ?? >>>>>>>>> >>>>>>>>> ...Jim Thompson >>>>>>>> >>>>>>>>Sorry. When the circuit is nominally on I want to make 12V from the 25V >>>>>>>>rail with a linear regulator. When the circuit is nominally off the 25V >>>>>>>>rail is at 4V, and I would like to effectively shut off the 12V line >>>>>>>>entirely. >>>>>>>> >>>>>>>>A 6.8V zener would make for around 18V at the input to the regulator, so >>>>>>>>the "on" part works fine. I'm just wondering if, with 4V on one side and >>>>>>>>a regulator input on the other, if the zener will flow some predictably >>>>>>>>low current. >>>>>>> >>>>>>>6.8V zeners suck. I'd just use an enable pin on the regulator. >>>>>> >>>>>>And if the regulator of choice has no ENABLE pin, then what? >>>>> >>>>>Then choose another, asshole. >>>> >>>>--- >>>>That's no help, since hostility leads, reductio ad absurdum, to war. >>>> >>>>Do you want to declare war with your limited resources? >>>>--- >>>> >>>>>When you want to discuss electronics, let us all know. >>>> >>>>--- >>>>I'm always up for that, but your invitation is preumptuous, as if you >>>>were running the game. >>>> >>>>JF >>> >>>That's silly. I'm running the game. >> >>--- >>Then you create unhappiness because you wallow in it? >> >>JF > >I create electronics because people need it.
--- Total nonsense. You don't create anything, you only rearrange (paint by numbers) what's already on tap in order to build machines which will do your customers' bidding. ---
>We just solved a problem with thrust measurement in a GTF. Things like >that are satisfying.
--- Indeed. you managed to sell a painting. John Fields
On Wed, 27 Jul 2016 22:20:27 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:


>What do you do?
Whatever I want to. John Fields
On Thu, 28 Jul 2016 18:49:53 -0500, John Fields
<jfields@austininstruments.com> wrote:

>On Wed, 27 Jul 2016 22:20:27 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>On Wed, 27 Jul 2016 21:34:19 -0500, John Fields >><jfields@austininstruments.com> wrote: >> >>>On Wed, 27 Jul 2016 14:57:59 -0700, John Larkin >>><jjlarkin@highlandtechnology.com> wrote: >>> >>>>On Wed, 27 Jul 2016 14:49:40 -0500, John Fields >>>><jfields@austininstruments.com> wrote: >>>> >>>>>On Sun, 10 Jul 2016 17:58:29 -0400, krw@attt.bizz wrote: >>>>> >>>>>>On Sun, 10 Jul 2016 16:01:50 -0500, John Fields >>>>>><jfields@austininstruments.com> wrote: >>>>>> >>>>>>>On Thu, 23 Jun 2016 22:49:35 -0400, krw <krw@nowhere.com> wrote: >>>>>>> >>>>>>>>On Thu, 23 Jun 2016 21:07:54 -0500, Tim Wescott <tim@seemywebsite.com> >>>>>>>>wrote: >>>>>>>> >>>>>>>>>On Thu, 23 Jun 2016 16:20:27 -0700, Jim Thompson wrote: >>>>>>>>> >>>>>>>>>> On Thu, 23 Jun 2016 17:42:40 -0500, Tim Wescott >>>>>>>>>> <seemywebsite@myfooter.really> wrote: >>>>>>>>>> >>>>>>>>>>>I know the theory, more or less. >>>>>>>>>>> >>>>>>>>>>>In practice, what's the reverse current through a zener diode at levels >>>>>>>>>>>well below the breakdown voltage? I've got a circuit where I'm feeding >>>>>>>>>>>a 12V linear regulator with a 25V line. It would be handy to put a >>>>>>>>>>>zener diode in there so that when the 25V line drops to 4V the current >>>>>>>>>>>into the regulator drops to tens of microamps. I'm wondering if a >>>>>>>>>>>series zener will do it. >>>>>>>>>> >>>>>>>>>> Clear as mud ;-) Post a schematic of what you mean... 25V -> 4V ?? >>>>>>>>>> >>>>>>>>>> ...Jim Thompson >>>>>>>>> >>>>>>>>>Sorry. When the circuit is nominally on I want to make 12V from the 25V >>>>>>>>>rail with a linear regulator. When the circuit is nominally off the 25V >>>>>>>>>rail is at 4V, and I would like to effectively shut off the 12V line >>>>>>>>>entirely. >>>>>>>>> >>>>>>>>>A 6.8V zener would make for around 18V at the input to the regulator, so >>>>>>>>>the "on" part works fine. I'm just wondering if, with 4V on one side and >>>>>>>>>a regulator input on the other, if the zener will flow some predictably >>>>>>>>>low current. >>>>>>>> >>>>>>>>6.8V zeners suck. I'd just use an enable pin on the regulator. >>>>>>> >>>>>>>And if the regulator of choice has no ENABLE pin, then what? >>>>>> >>>>>>Then choose another, asshole. >>>>> >>>>>--- >>>>>That's no help, since hostility leads, reductio ad absurdum, to war. >>>>> >>>>>Do you want to declare war with your limited resources? >>>>>--- >>>>> >>>>>>When you want to discuss electronics, let us all know. >>>>> >>>>>--- >>>>>I'm always up for that, but your invitation is preumptuous, as if you >>>>>were running the game. >>>>> >>>>>JF >>>> >>>>That's silly. I'm running the game. >>> >>>--- >>>Then you create unhappiness because you wallow in it? >>> >>>JF >> >>I create electronics because people need it. > >--- >Total nonsense. > >You don't create anything, you only rearrange (paint by numbers) >what's already on tap in order to build machines which will do your >customers' bidding.
Well, Shakespeare just rearranged letters. We rearrange parts. That's what electronic design is, selecting and connecting parts. If you think that's trivial, why do you post to SED?
>--- > >>We just solved a problem with thrust measurement in a GTF. Things like >>that are satisfying. > >--- >Indeed. > >you managed to sell a painting.
We did some Fourier analysis and told the user how to filter out test stand vibration modes. The engine stand is a huge structure that sits on a gigantic concrete footing. Unfortunately, it's in Florida and under the footing is mush. What are you doing these days? Something creative? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com