Zener kinda turns on

[Fred Abse]

Version that turns 5V LED off when 12V LED turns on with sufficient current:

For me, using LTSpice, that switches at about 14 volts.

5V indicator draws 2mA at 5V input.then rises to over 10mA before
switching off. "12V" LED makes about 1.5mA at *15V* input.

Use a .dc sweep analysis. you'll see what I mean.

 

[Klaus Kragelund]

I don't get it. At 12 volts, the "12V" LED is off and the "5V" LED is on. At 15

volts, both LEDs are on, although the "12V" is dim.



At Vcc=5, "12" is off and "5" might be on.

No. At 5V ish (gate source threshold, the 5V LED is on. At 12V ish and beyond, both LEDs are on

Regards

Klaus

 

[Klaus Kragelund]

For me, using LTSpice, that switches at about 14 volts.



5V indicator draws 2mA at 5V input.then rises to over 10mA before

switching off. "12V" LED makes about 1.5mA at *15V* input.



Use a .dc sweep analysis. you'll see what I mean.

Well, I did. This circuit is not intended for precision and neither are the values picked thoroughly for the precise voltage levels, just depiction of the general idea.

Regards

Klaus

 

[Klaus Kragelund]

That is, as they say, "component rich."



This should work:



https://dl.dropboxusercontent.com/u/53724080/SED/LEDs_5_12.JPG



It could have a bandgap in the "13K" leg, but it really doesn't need

it.

This is going to vary much with temperature and production spread of the VBE of the BZX70 transistor for the 12V level. The same for

Cheers

Klaus

 

[josephkk]

It will work, with about a fifth as many parts as the insane brute-forcejoke
you posted.

Try again, something realistic this time. Use a 555 or something, beforeJF
beats you to it.

Cool beans idea. I already see how to do it with a 7555. If i can get
LTSpice to cooperate enough i will even post it.

?-)

 

[Jasen Betts]

Cool beans idea. I already see how to do it with a 7555. If i can get
LTSpice to cooperate enough i will even post it.

here's one way.

+----+---------+------------+-- 5V/12V
| | | |
| | | V
| | | T \\ 5V
| | . . . .|. . . . |
| | . VCC(8) . 330
| | . . |
10k +---RES(4) OUT(3)------+
| . 555 . |
+--------TH(6) DIS(7)-- 1K
| . . |
+-Z<-+---TR(2) CV(5)-- V
| . . T \\ 12V
3v3 | . GND(1) . |
| . . . .|. . . . |
| | |
| | |
+---------+------------+-- 0V

Zener diodes operating at any voltage between 2.0V and 3.9V are suitable
or you could use a blue LED forwards biased.

 

[Jasen Betts]

here's one way.

+----+---------+------------+-- 5V/12V
| | | |
| | | V
| | | T \\ 5V
| | . . . .|. . . . |
| | . VCC(8) . 330
| | . . |
10k +---RES(4) OUT(3)------+
| . 555 . |
+--------TH(6) DIS(7)-- 1K
| . . |
+-Z<-+---TR(2) CV(5)-- V
| . . T \\ 12V
3v3 | . GND(1) . |
| . . . .|. . . . |
| | |
| | |
+---------+------------+-- 0V

Zener diodes operating at any voltage between 2.0V and 3.9V are suitable
or you could use a blue LED forwards biased.

on rethinking that circuit doesn't make any sense,
I think I must have been was using a damaged 555 when
I got that to work,

 

[Jasen Betts]

on rethinking that circuit doesn't make any sense,
I think I must have been was using a damaged 555 when
I got that to work,

maybe with a zener twice the size,

 

[Jamie]

here's one way.

+----+---------+------------+-- 5V/12V
| | | |
| | | V
| | | T \\ 5V
| | . . . .|. . . . |
| | . VCC(8) . 330
| | . . |
10k +---RES(4) OUT(3)------+
| . 555 . |
+--------TH(6) DIS(7)-- 1K
| . . |
+-Z<-+---TR(2) CV(5)-- V
| . . T \\ 12V
3v3 | . GND(1) . |
| . . . .|. . . . |
| | |
| | |
+---------+------------+-- 0V

Zener diodes operating at any voltage between 2.0V and 3.9V are suitable
or you could use a blue LED forwards biased.

I am afraid that isn't going to work that way, for a couple of reasons.

1. You have the output orientations backwards. The Threshold point
will turn off the output, which will then activate the upper LED. Simply
change the labeling for those two to fix that.

2. Internally you have a voltage divider of 1/3 and 2/3 of the Vcc,
since you are raising the Vcc, it'll never reach the threshold. To fixed
that, you need to supply the Vcc with a fixed 5 volt or less supply.
Also, you most likely can tie both the trigger and threshold together.

When it's all put together with the proper voltage divider, that will
work nicely.. Don't forget that you can use the Discharge output to
drive an LED. You don't need that zener unless you want to protect
the inputs from over 5 volts and the Vcc rail could be supplied via a
basic 78L05 reg..

Jamie

 

[Jasen Betts]

Remember that time I micowaved a 555 and busted it and then toasted it
and got it "working" again? the above circuit was woring with that 555
r> I am afraid that isn't going to work that way, for a couple of reasons.

1. You have the output orientations backwards. The Threshold point
will turn off the output, which will then activate the upper LED. Simply
change the labeling for those two to fix that.

With a 12V supply the zener comes out below 1/3 VCC and the 555 is
basically an inverter so a low input converts to a high output
lighting the lower LED

What i'm doing is comparing the internal divider with an
low precision refernece voltage from the zener

2. Internally you have a voltage divider of 1/3 and 2/3 of the Vcc,
since you are raising the Vcc, it'll never reach the threshold. To fixed
that, you need to supply the Vcc with a fixed 5 volt or less supply.

Why? the divider's right. I had the trigger and threshold pins
connections wrong though.

If you tie the threshold pin high the trigger pin controls the
output and that inconvenient 1/3 VCC hysteresis dissapears.

Also, you most likely can tie both the trigger and threshold together.

yeah, but if you do that the hysteresis makes input voltage more critical


Corrected version:

+----+---------+------------+-- 5V/12V
| | | |
| | | V
| | | T \\ 5V
| | . . . .|. . . . |
| | . VCC(8) . 330
| | . . |
1K +---RES(4) OUT(3)------+
| | . 555 . |
| +---TH(6) DIS(7)-- 1K
| . . |
+--------TR(2) CV(5)-- V
| . . T \\ 12V
3V3 Z . GND(1) . |
zener A . . . .|. . . . |
| | |
| | |
+--------------+------------+-- 0V


I rediced the 10K to 1K to make the zener behave a little better
those 3V3 parts are real mushy.

With 3.3V on pin 2 VCC anywhere above 10V registers lights the 12V
LED and the lower voltages light the other one

 

[Jasen Betts]

You can do it quite nicely with a 556 (dual 555)...

http://www.analog-innovations.com/SED/Panfilero_LED-v556.pdf

2 555s, a voltage reference, and two transistors,
unreal! also, it seems to answer the question.

You can also do it easily with an LM339.

Yeah, that's going to be much more fun
it needs another part, they're cheaper parts

+-----------+--------------+-----+-- +3-16V
| | | |
33K V V |
| T\\ 12V T\\5V |
| | | |
| +-----------------------+ |
| | | | |
| | +--------100K--+ |
| | | | |
| | 2K2 680R |
| | + | - | |
| +--|\ +-------|\ | [LM339]
| | >---+ | >----+ |
+-----|/ +--|/ |
| - | + |
+----------------+ |
| |
100K |
| |
+--------------------------------+-- 0V

 

[[email protected]]

On Sunday, April 21, 2013 4:28:38 PM UTC-4, John Larkin wrote:

Are you still fiddling with this lame nothing circuit?

 

[[email protected]]

John Larkin Highland Technology, Inc



jlarkin at highlandtechnology dot com

http://www.highlandtechnology.com



Precision electronic instrumentation

Picosecond-resolution Digital Delay and Pulse generators

Custom laser drivers and controllers

Photonics and fiberoptic TTL data links

VME thermocouple, LVDT, synchro acquisition and simulation

Circuit engineer is right, you do seem to be going around in circles on this one

 

[Jamie]

If you tie the threshold pin high the trigger pin controls the
output and that inconvenient 1/3 VCC hysteresis dissapears.




yeah, but if you do that the hysteresis makes input voltage more critical


Corrected version:

+----+---------+------------+-- 5V/12V
| | | |
| | | V
| | | T \\ 5V
| | . . . .|. . . . |
| | . VCC(8) . 330
| | . . |
1K +---RES(4) OUT(3)------+
| | . 555 . |
| +---TH(6) DIS(7)-- 1K
| . . |
+--------TR(2) CV(5)-- V
| . . T \\ 12V
3V3 Z . GND(1) . |
zener A . . . .|. . . . |
| | |
| | |
+--------------+------------+-- 0V


I rediced the 10K to 1K to make the zener behave a little better
those 3V3 parts are real mushy.

With 3.3V on pin 2 VCC anywhere above 10V registers lights the 12V
LED and the lower voltages light the other one

I forgot about the TR dominating the THR as a momentary switch while
the THR is being held.

Years ago I made an array of 556's on a board as run/jog/stop operator
logic switches.



Sink Logic

Vcc
|
NC .-.
E-Stop STOP | | PUll UP
NC | |
T T '-'
--- --- |
-o o-+-----+-------+-o o+-----------------------+Threshold
|
|
|
|
|
| T
| --- +
+--------+-o o+---------------------- Trigger

START/JOG (NO) Hold STOP for jog function.
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

We considered using RS FF but they didn't offer the flexibility of a
timer and also, with the timer, we could simply add a time effect to it
if we needed a TimeOff/On delay, which we also do that with jumper
options and places to put the RC components in for each zone. These were
put in custom card slots as modular systems and proved to work very nicely.

I know one of these systems is still operating because I've had to
service it for minor details, like dried out caps etc..

So your circuit does agree with me, thanks for the drive down memory
lane

Jamie

 

[josephkk]

Spice'ing it is no challenge. Draw something with a pencil, or better yet a pen,
that will work first time.

Like your crappy drawings? No thanks. One of my main uses for LTspice is
schematic capture. Much nicer output, easy to put part values in
(especially when you can find semiconductors reasonable close to what you
want). Plus if anyone wants to challenge it they have a plenty good file
to work from.

Of course i could use my antique Tango Schematic, or my equally antique
Circad pretty much as easily.

?-)

 

[josephkk]

All the circuits that I posted would work. One of yours is a clumsy
hairball, and the other one is plain wrong.

Actually several of them may or may not work depending on all the unstated
part values. Oh, now i remember you post topologies that might work if
proper parts values were used, but you never calculate anything through
around here.

Pretender.

?-)

 

[josephkk]

The challenge is to *design* something that works, not to Spice it and fiddle
until it seems to work.

You clearly DID NOT READ what i posted. Lame flame.

?-)

 

[josephkk]

I mostly post circuits. If you perceive my circuits as "braggadocio" youmust
think that they are pretty good. Thanks for the compliment.

Poor self deluded Larkin, doesn't understand braggadocio is an insult,
similar to "talking trash" or lying.

 

[josephkk]

On Tue, 23 Apr 2013 17:54:37 -0500, John Fields

On Tue, 23 Apr 2013 12:27:24 -0500, John Fields

On Tue, 23 Apr 2013 09:24:04 -0700, John Larkin

On Mon, 22 Apr 2013 22:34:47 -0700, John Larkin


Sometimes I post schematics with values, sometimes Spice sims, sometimes sheets
from actual products.

---
But mostly you post braggadocio.

I mostly post circuits. If you perceive my circuits as "braggadocio" you must
think that they are pretty good. Thanks for the compliment.

---
No compliment intended, and you don't mostly post circuits, you mostly
post self-aggrandizing rhetoric exalting yourself at the expense of
others.
---

Your LED thing is OK, but it does have a dead zone.

---
You shouldn't me making commentary if you don't read the spec's.

Panfilero wrote: "I was making a circuit that when you power it up
with 5V a 5V LED indicator turns on and if you power it up with 12V
the 5V LED goes off and the 12V indicator goes on."
---

You could eliminate that and
reduce the parts count by taking the output of one comparator, inverting it, and
driving the second LED.

---
That's just klunky.

Here's a rather less klunky way of doing it:


+5/12>--+---------+-------+--[5k1]--+
| | | |
[430R] [10k] | [LED] 12V IN
| | | |
| 3.3V +------|-\ |
|/ | | >-------+
+---------|------|+/TLV7211 |
| | | |
[1N5226B] [5k1] | [LED] 5V IN
| | | |
GND>----+---------+-------+--[1k5]--+

---
Just for grins, using LTC library parts:

Version 4
SHEET 1 880 680
WIRE 128 -16 -192 -16

Full .ASC file at...
Message-ID: <https://dl.dropboxusercontent.com/u/53724080/Optos/LED_Diff_Pair.JPG>

SYMATTR InstName U1
TEXT -160 384 Left 2 !.tran 5 uic

Looks like the LTspice LED model is for a white LED. That's why I
just reworked my PSpice libraries so that "RED" definitely calls up a
RED model.

---

So what?

The topology remains the same and all that changes is the values of
the resistors.

Just advisory. I wasn't criticizing. The libraries in LTspice can
mislead.

...Jim Thompson

That is true, every spice can. I wish LTspice had a complete set of LT
parts as well, but it doesn't.

?-)

 

[Fred Abse]

Went to an MIT wine tasting last night at il Vinaio (270 W Main St Mesa,
AZ, Great Place!). I have to adopt and modify a Henny Youngman phrase
scrolled on the wall: "I just turned 73, but I still don't need glasses.
I just drink straight from the bottle" ;-)

Just so long as you don't adopt his "signature" catchprase.