Zener kinda turns on

or turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

F until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be of f at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

1k maybe, but why is D1 turning on at all?  Is it leakage current that's causing this circuit not to work at 5V?  D3 the 12V LED is definitely of f at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

That 12V zener is not doing very much...

But look at an I-V curve for the 5.6V zener, I'd guess there's still some current flow at 5.0V. If the FET gate is at 1 V then you have ~1uA of current flowing through the zener.

George H.

On a sunny day (Wed, 17 Apr 2013 08:42:50 -0700 (PDT)) it happened panfilero wrote in :

0 to +12 V +---------------------------------------- | | | | | --- --- | | \ /// \ /// [ ] 10 K | --- LED1 --- LED2 | R3 [ ] 1k | | | | R1 c c | |------b NPN NPN b-------| | e------------------e | --- Q1 | Q2 | / | | / \ 5.6V [ ] 470 [ ] 10K --- zener | R2 | R4 | /// /// ///

Differential?

At link is below

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

You need a lower R2 or a different circuit. Low voltage zeners don't have super sharp knees.

--

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

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

Err...it takes about 4V to turn on a "typical" LED, so use of a 5V (or even 3V) zener will guarantee no light from the LED.

"Robert Baer"

** D4 is the 5V LED, D3 is the 12V LED.

The dopey OP has failed to allow for leakage current in the 5.6 V zener and is trolling us as usual.

... Phil

Call it leakage or what you will -- zeners do not have sharp corners in their I-V characteristic.

_Always_ study the data sheet of the part you're going to use. In the case of two-terminal parts, _always_ know what the I-V characteristic is. It's _never_ as simple as the basic books would have you believe.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

A wee bit overkill...

but Perfectionist 'R' Us >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

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

This should work:

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

--

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

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

Here' in the trailer park, we'd have just painted the 5V power plug red and the 12V one green.

Over in town, they'd have used a dual-color LED, put a zener in series with the red one and called it green and orange.

Or use rectangular LEDS and call it a bar graph. Probably works better for the color-blind.

I've hosted a bunch of design reviews. Seen a lot of "solutions" that were WAY out of proportion to the root problem being addressed. Often comes under the heading "dimininishing returns". ;-)

KISS 'R' US...

turns on and if you power it up with 12V the 5V LED goes off and the 12V indicator goes on.

until I provide it a voltage drop of 5.6V, and since it's in series with some other stuff (resistors and an LED) I thought it would definitely be off at 5V, but it's on just enough to turn on my FET M1 and not let my D4 LED light up... I'm basically measuring a little over 1V at the gate.

maybe, but why is D1 turning on at all? Is it leakage current that's causing this circuit not to work at 5V? D3 the 12V LED is definitely off at a 5V supply (as it should be) and the circuit works at 12V... but not at 5V...

Well! I _did_ say that it was a wee bit overkill, but it _does_ perform _exactly_ as requested >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Le Wed, 17 Apr 2013 08:42:50 -0700, panfilero a écrit:

The idea is good.

Change your zener for a 7.5V one (which being an avalanche one will be much 'stiffer'), lose R3, and as you said make R2 10K to be safer and you're done.

You don't need D2.

--
Thanks, 
Fred.

Hey, I just invented the LED differential pair!

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

s r

nt

at

OK I'm most likely just slow this morning, but how does that turn off the one LED when the transistor turns on? And doesn't it turn on the first LED at ~ 2volts or so. How about if you put a second LED in the leg without the transistor? Then it would turn on at ~4 volts and turn off with current through the transistor.

I like Jan's circuit.

George H.

.highlandtechnology.com  jlarkin at highlandtechnology dot com

Or simply a common diode.

You also get varying currents between 5V and 12V due to the resistor setting the current.

Incwww.highlandtechnology.com  jlarkin at highlandtechnology dot com

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

That works, but it needs seven parts to drive the LEDs, which is a lot better than Jim's 19. Here are a few more with 4 or 5:

I really like "A" for its elegant symmetry.

This takes 6 parts, but it's power efficient, as is Jan's circuit, with a little tweaking.

This is fun, like crossword puzzles. Doesn't anybody want to play?

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

Different color LEDs have different forward voltages. Use, say, blue on the right and red on the left.

And doesn't it turn on the

Sure.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

Or pick the LEDs properly.

It's supposed to show if the supply is +5 or +12.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

Not a particularly good circuit...

A & B waste current, conducting 2x LED current at 12V. C is wishful, let's see some numbers.

little

That works, dunno why you need a FET though.