# Zener diode below-threshold reverse current

Started by 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.
>>>
>>>---
>>>
>>>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:

>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:
>
>>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/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
>>
>> 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:
>
> >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.
>>>>
>>>>---
>>>>
>>>>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.
>>>>>
>>>>>---
>>>>>
>>>>>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

```