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 Forum index » DIY Hardware and Software
Voltage limiter
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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Fri Aug 23, 2013 2:18 am    Post subject: Voltage limiter Reply with quote  Mark this post and the followings unread

I found a voltage limiter circuit (actually two. one for +/- and one for + limited output):

+/- limitation:
http://www.circuitstoday.com/wp-content/uploads/2011/06/Op-Amp-comparator-circuit.jpg

+ limitation
http://www.circuitstoday.com/wp-content/uploads/2011/06/Op-amp-comparator-circuit-.jpg

The explanations here:

http://www.circuitstoday.com/voltage-limiter-circuit-using-op-amp

Let's say I want to limit a voltage to +/- 5v (I don't mean a constant output, but a limited one, no matter the input). Do I simply need to choose 2 diodes with each 5v zener voltage like this one here and that's it ?
Is R value then negligeable (referring to the images I posted) ?

Do I understand well ? It this so simple ?
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JingleJoe



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PostPosted: Fri Aug 23, 2013 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

wait wait hold on, you just want straight, DC 5 volts?... you're making this an awful lot more complex than it needs to be, just use a voltage regulator. L7805 should do the trick.
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elmegil



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PostPosted: Fri Aug 23, 2013 11:15 am    Post subject: Reply with quote  Mark this post and the followings unread

I think he wants a variable signal clamped to stay between + / - 5V, Joe.
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JingleJoe



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PostPosted: Fri Aug 23, 2013 11:31 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
I think he wants a variable signal clamped to stay between + / - 5V, Joe.

Quite right
I misread something the OP was saying Rolling Eyes

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sneakthief



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PostPosted: Fri Aug 23, 2013 12:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Schottky to the rescue:

http://www.eevblog.com/forum/projects/pic-input-protection-using-a-zener-diode/msg21840/?PHPSESSID=33bbdf2e2a88957db87cce882680f1ca#msg21840

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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Fri Aug 23, 2013 4:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
I think he wants a variable signal clamped to stay between + / - 5V, Joe.

Exactly, thank you. Not constant.

Could be a positive limiiter. It's only to understand the principle.
For instance it could be a circuit which takes all voltages below 0v to 0v and all above 5v to 5v.

Or even a neg/pos limiter. Limiting for instance all voltages below -5v to -5v and all above 5v to 5v.
Like in the images I posted before where I was asking me if I'd only need the right diodes to achieve this, no matter what R has for value, or if it would need more than 5v diodes.
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PHOBoS



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PostPosted: Sat Aug 24, 2013 5:20 am    Post subject: Reply with quote  Mark this post and the followings unread

hmm, well I wouldn't just call this is a limiter, it's more like a limited comparator. So the output will always be either the max. or min. voltage
not something in between (as is also shown in the examples). Maybe this is what you want.

However, if you just want to limit the output signal while still having a varying (analog) voltage, you can use the zenerdiode(s) on the output.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Tue Aug 27, 2013 12:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
hmm, well I wouldn't just call this is a limiter, it's more like a limited comparator. So the output will always be either the max. or min. voltage
not something in between (as is also shown in the examples). Maybe this is what you want.

However, if you just want to limit the output signal while still having a varying (analog) voltage, you can use the zenerdiode(s) on the output.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

I would like to limit the voltages when they are below 0v to 0v and when they are above +5v than to +5v. All the rest remains.
Looking at your illustration, I realize how simple it is in fact. Thank you !


PHOBoS wrote:
hmm, well I wouldn't just call this is a limiter, it's more like a limited comparator. So the output will always be either the max. or min. voltage not something in between (as is also shown in the examples). Maybe this is what you want.

I will take then again a look at the images I posted because I did not know these were only ouzputting either max or min voltage, not exactly what I was looking for. I thought they would also leave the voltage unchanged between 2 values. It is good you told me they would not, it will help me understand better.
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JingleJoe



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PostPosted: Wed Aug 28, 2013 2:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah phobos's second circuit can be acheived with ordinary diodes, pointing in oposite directions, connected in parallel Smile but then you are subject to the low forward voltages of the diodes (usually about 0.6volts) but you could attenuate your signal down before the input and amplify it back up at the output if you were really strapped for zeners.
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PHOBoS



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PostPosted: Wed Aug 28, 2013 6:40 am    Post subject: Reply with quote  Mark this post and the followings unread

yes,. 2 diodes antiparallel is a method often used as a limiter in audio
circuits, where the low levels don't matter that much. Sometimes LED's
are used which, depending on the color, have a higher forward voltage.
You could also put a couple of diodes or LEDs in series, in which case the
voltages add up.

some info here

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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Wed Aug 28, 2013 9:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you very much for the explanations. Great !

rogerlatur wrote:
PHOBoS wrote:
hmm, well I wouldn't just call this is a limiter, it's more like a limited comparator. So the output will always be either the max. or min. voltage not something in between (as is also shown in the examples). Maybe this is what you want.

I will take then again a look at the images I posted because I did not know these were only outputting either max or min voltage, not exactly what I was looking for. I thought they would also leave the voltage unchanged between 2 values. It is good you told me they would not, it will help me understand better.

I had a look at the pictures again.
As I see the waveform between Vp and -Vp, I didn't realize the output was either the max (Vp) or min. voltage (-Vp ) and not something in between.
To me it looked like a limitation at Vp and -Vp (because of the waveform shown between these 2 points), not going below -Vp or above Vp and leaving the voltage unchanged between Vp and -Vp. I thought it was the same principe as the wikipedia illustration posted by PHOBoS.
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rogerlatur



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PostPosted: Fri Sep 13, 2013 11:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Reading again all posts after a while and I would like to thank you again for all your help here !

JingleJoe wrote:
Ah phobos's second circuit can be acheived with ordinary diodes, pointing in oposite directions, connected in parallel Smile but then you are subject to the low forward voltages of the diodes (usually about 0.6volts) but you could attenuate your signal down before the input and amplify it back up at the output if you were really strapped for zeners.


PHOBoS wrote:
yes,. 2 diodes antiparallel is a method often used as a limiter in audio
circuits, where the low levels don't matter that much. Sometimes LED's
are used which, depending on the color, have a higher forward voltage.
You could also put a couple of diodes or LEDs in series, in which case the
voltages add up.

some info here


All is really clear after re-reading (long digestion time ?).
Also I realize I should be more clear in my questions: *between, above, below...*. A schema would make all much more easy to explain in english. I will do so in the future for this kind of questions.

You guys are really amazing !
And I am very lucky to have a place like here. Very Happy
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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Sat Sep 14, 2013 12:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Reading again all posts after a while and I would like to thank you again for all your help here !

JingleJoe wrote:
Ah phobos's second circuit can be acheived with ordinary diodes, pointing in oposite directions, connected in parallel Smile but then you are subject to the low forward voltages of the diodes (usually about 0.6volts) but you could attenuate your signal down before the input and amplify it back up at the output if you were really strapped for zeners.


PHOBoS wrote:
yes,. 2 diodes antiparallel is a method often used as a limiter in audio
circuits, where the low levels don't matter that much. Sometimes LED's
are used which, depending on the color, have a higher forward voltage.
You could also put a couple of diodes or LEDs in series, in which case the
voltages add up.

some info here


All is really clear after re-reading (long digestion time ?).
Also I realize I should be more clear in my questions: *between, above, below...*. A schema would make all much more easy to explain in english. I will do so in the future for this kind of questions.

You guys are really amazing !
And I am very lucky to have a place like here. Very Happy


http://www.allaboutcircuits.com/vol_3/chpt_3/6.html#zenerclip
Very useful !
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