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Topic Title: Attenuating AC signals
Topic Summary: Can you use a voltage divider?
Created On: 15 March 2012 11:06 AM
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 15 March 2012 11:06 AM
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safortune

Posts: 8
Joined: 27 October 2010

Hi, apologies for asking such an easy question, however, I was wondering if you can use a voltage divider to attenuate AC signals as well as DC?

If yes, what are the advatages of using an attenuator chip over a crude voltage divider (if any)?

Any and all help/information would be much appreciated...

Thanks,

Steve
 15 March 2012 01:24 PM
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ANFierman

Posts: 136
Joined: 25 July 2008

Have a look here:

https://www.circuitlab.com/circuit/5jj6sj/resistor_attenuator/



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Andy Fierman

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http://signality.co.uk
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 15 March 2012 01:57 PM
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amillar

Posts: 1918
Joined: 28 May 2002

What do you mean by an attenuator chip? Can you give an example?

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
 15 March 2012 03:59 PM
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safortune

Posts: 8
Joined: 27 October 2010

Andy M, I was thinking about something such as IMS A-1612.

However the link Andy F provided was very clear and answered my question. Cheers Andy F.

I knew it was an easy question just had one of those moments when you doubt yourself.

Thanks for your help guys. Stephan
 16 March 2012 08:46 AM
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amillar

Posts: 1918
Joined: 28 May 2002

Good stuff.

Just for info, this chip will be just a collection of resistors forming (effectively) a voltage divider, the advantage of a device like this is that all the resistors can be perfectly matched (possibly laser trimmed?) by the manufacturer, so it will be much more accurate than an attenuator built using off-the-shelf resistors.

Often you don't need that much accuracy, or for a one-off you can hand select the resistors, but for high accuracy production volumes the chip is better.

Cheers,

Andy

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Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
 23 March 2012 07:44 AM
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nicolsaaa

Posts: 2
Joined: 23 March 2012

what is the meaning of attenuate AC ???


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lalinguaarabapertutti.com

Edited: 30 March 2012 at 07:54 AM by nicolsaaa
 23 March 2012 09:04 AM
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ANFierman

Posts: 136
Joined: 25 July 2008

Attenuate = make smaller.

AC = Alternating Current, in other words a varying voltage or current signal.

As in:

https://www.circuitlab.com/circuit/5jj6sj/resistor_attenuator/

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Andy Fierman

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http://signality.co.uk
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 10 May 2013 04:04 PM
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kengreen

Posts: 400
Joined: 15 April 2013

Pardon me but there is some confusion here. If you wish to attenuate a CURRENT signal then you must use a current-divider. It is the same beastie as a voltage-divider except that you connect it back-to-front; i.e. the current-signal goes in at the tapping point and the attenuated signal is taken from across the entire circuit. You may have to add a padding resistor in series with the input to a variable attenuator to prevent short-circuiting the driver at minimum output.

The lower part of this divider shunts unwanted current from the i/p to the transistor.

Ken Green


I
 10 May 2013 05:03 PM
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ANFierman

Posts: 136
Joined: 25 July 2008

To illustrate Kens point, I have updated:

https://www.circuitlab.com/circuit/5jj6sj/resistor_attenuator/

to include an example of a current divider for attenuating currents as well as the original potential divider for attenuating voltages.

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Andy Fierman

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http://signality.co.uk
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 23 May 2013 06:10 AM
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sandip

Posts: 21
Joined: 31 March 2013

Can potentiometer be an example of current divider.

Regards,

Sandip Roy.
 23 May 2013 08:41 AM
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ectophile

Posts: 544
Joined: 17 September 2001

Potentiometers are normally used as voltage dividers. But given a constant-current source, I can see a way to use one as a current divider.

Connect the AC source to the slider. Connect one end of the track to the AC sink. Connect the other end of the track, through the load, to the AC sink.

(By "source" and "sink", I just mean the two ends of the current-limited AC supply)

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S P Barker BSc PhD MIET
 23 May 2013 08:55 AM
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ANFierman

Posts: 136
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In my example on CircuitLab:

https://www.circuitlab.com/circuit/5jj6sj/resistor_attenuator/

you can visualise what ectophile is explaining by considering the "ac2" node at the junction of R5 and R6 as being the slider of the potentiometer and the grounded ends of R5 and R6 being each end of the potentiometer.

If you run the simulation, you can see how the total current from the AC current source Iac1 is shared in inverse proportion to the values of R5 and R6.

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Andy Fierman

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http://signality.co.uk
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 28 August 2013 03:17 AM
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kengreen

Posts: 400
Joined: 15 April 2013

a bit late in the day but it is the first time that I have returned to this thread.

The term potentiometer (contracted to pot' meter) was/is a misuse of a device-name that arose in the sacred halls of academia mainly in connection with their BBBB-s (brass bound buggery boxes) - things of great beauty and exquisite accuracy but, although they may be useful, are not truly prized in a modern laboratory or workshop.

Today the word in general refers to a mechanically operated variable resistor which is manufactured to handle a variety of powers. It can be used as a voltage-divider, a current divider, a signal divider, a direct-voltage adjuster... name your poison!
Ken Green
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