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Can Step up transformer amplify signals?

by bukks bunny
Tags: amplifier, transformer, voltage gain
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bukks bunny
#1
Jan31-13, 08:13 AM
P: 4
Hello friends.I was just wondering if a step up transformer can be used to amplify voltage signals like a transistor,as it step up input voltage at its output.?
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sophiecentaur
#2
Jan31-13, 08:35 AM
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Hi. Sorry, but you never get something for nothing.
A transformer is a Passive device. It cannot supply any extra power. It can change the voltage but the power it can provide will be no more than the original signal. A transistor, otoh, uses power from a supply (battery etc) to Amplify a signal; it is an Active device and can give you more signal power. That's the difference.
If you have a problem with all that then you need to find out about Volts, Current, Resistance and Power and what the terms actually mean. The basics are fairly approachable.

If you have a signal from a source that will supply a lot of current at a low voltage, then a transformer may be able to change that signal so its voltage swing is greater but it will only supply correspondingly less current into a load.
nsaspook
#3
Jan31-13, 10:50 AM
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A normal transformer can't provide power gain but it's possible to control the "energy coupling" from input to output with a low power signal using a 'Mag-Amp".

http://www.youtube.com/watch?v=DBX1-POuJMw

http://en.wikipedia.org/wiki/Magnetic_amplifier

sophiecentaur
#4
Jan31-13, 11:02 AM
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Can Step up transformer amplify signals?

Quote Quote by nsaspook View Post
A normal transformer can't provide power gain but it's possible to control the "energy coupling" from input to output with a low power signal using a 'Mag-Amp".

http://www.youtube.com/watch?v=DBX1-POuJMw

http://en.wikipedia.org/wiki/Magnetic_amplifier
You should make it clear that the signal in this case, also, uses / controls an external source of power,
nsaspook
#5
Jan31-13, 11:22 AM
P: 594
Quote Quote by sophiecentaur View Post
You should make it clear that the signal in this case, also, uses / controls an external source of power,
Sure, the energy of the control signal is not being boosted but a small change in signal input power can cause a large change in external power only using the magnetic fields of transformers so it meets the classic definition of a amplifier.
sophiecentaur
#6
Jan31-13, 11:30 AM
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I know you know - it was for the OP's benefit.
nsaspook
#7
Jan31-13, 12:05 PM
P: 594

Ferromagnetic circuits just keep coming back, this technology is slowly becoming mainstream again and could be what's next after CMOS (Intel is spending money for research).
http://ussc90.nl/circ.htm
http://en.wikipedia.org/wiki/Spintronics
unclebob
#8
Jan31-13, 01:01 PM
P: 6
hi guys: So is it a signal or out put power that's in question? A signal being used as a control?
nsaspook
#9
Jan31-13, 03:27 PM
P: 594
Quote Quote by unclebob View Post
hi guys: So is it a signal or out put power that's in question? A signal being used as a control?
Not sure what you mean but we were just making sure the OP understood my response to the question. A simple input/output transformer is not an amplifier but it is possible to design a transformer circuit that can operated as a amplifier.

In a MAG-AMP the signal is a input control that's external to the output but so is the signal in a electron tube or a FET (usually).
Nuclear_chita
#10
Feb1-13, 01:15 AM
P: 3
Nope, and yes may be. it depends upon your source. if it is capable to supply larger currents then yes. If you want to increase voltage and amount of current does not matter for you then obviously transformer can amplify the voltage(but current will be reduced to make the power constant p=vi).

Imp Note: It also depends on your signal. If frequency is too high then input inductance will eat out your signal resulting in attenuated signal at out put. Also high frequency signals require special core transformers having ceramic cores. Ordinary transformers don't work there.
nsaspook
#11
Feb1-13, 09:43 AM
P: 594
Quote Quote by Nuclear_chita View Post
Nope, and yes may be. it depends upon your source. if it is capable to supply larger currents then yes. If you want to increase voltage and amount of current does not matter for you then obviously transformer can amplify the voltage(but current will be reduced to make the power constant p=vi).
I think most of use would use the word "amplify" to mean (possible) power gain in a circuit. The input/output function of a "Step up" transformer (a component in a circuit) is not an amplifier because it's a unity or less power transformation that only changes the ratio of voltage and current.

My mag-amp example may have muddied the waters a bit but it's a good example of how a component when operated in a non-linear (core saturation) manner can provide power gain in a circuit without what we would normally think as 'active' components.
sophiecentaur
#12
Feb1-13, 10:13 AM
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It's ok if we define an active component as one that requires an external power source for it to work. Magnetic, thermionic or semiconductor would all qualify.
A 'transformer' merely 'transforms' impedance and supplies no extra power.
skeptic2
#13
Feb1-13, 12:55 PM
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Quote Quote by bukks bunny View Post
Hello friends.I was just wondering if a step up transformer can be used to amplify voltage signals like a transistor,as it step up input voltage at its output.?
OP specifically asked about amplifying voltage and it most of the responses discuss amplification in terms of power.

The quick answer is yes, a step-up transformer can amplify voltage. Let me give you an example. I was working for a company that used ferrite antennas resonant to 200 kHz. The coil around ferrite rod had a low impedance tap to connect to the coax cable. In order to improve the range I discovered by supplying DC through the cable, I could operate a single stage FET amplifier with the gate connected across the full coil instead of just the low impedance tap. Sure the FET added gain but not as much as the difference between using the voltage across the full length of the coil and the tap.
sophiecentaur
#14
Feb1-13, 01:35 PM
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Quote Quote by skeptic2 View Post
OP specifically asked about amplifying voltage and it most of the responses discuss amplification in terms of power.

The quick answer is yes, a step-up transformer can amplify voltage. Let me give you an example. I was working for a company that used ferrite antennas resonant to 200 kHz. The coil around ferrite rod had a low impedance tap to connect to the coax cable. In order to improve the range I discovered by supplying DC through the cable, I could operate a single stage FET amplifier with the gate connected across the full coil instead of just the low impedance tap. Sure the FET added gain but not as much as the difference between using the voltage across the full length of the coil and the tap.
This can be dismissed as a matter of semantics but I feel it's more important than that.
The word 'amplification' is used, loosely (sloppily, even) in both cases but it strictly means 'making a signal bigger' i.e. more powerful. When specifying the performance of an 'amplifier'. Often, you'll find the expression Voltage Gain is used. It's a very useful piece of information but, without other information says absolutely nothing about the Power Gain, which is always what is really important. Unless input and output impedances are specified you have no idea how much use the amplifier will be (or the signal emerging)..
If I go into a shop and buy a 10dB Amplifier then I assume it will make an input signal ten times more Powerful - which is what counts.
You can only talk in dB, in a valid way, when you mean a gain in power. As it happens, when you are operating with the same impedances, the voltage gain can be calculated from the specified gain in dB - but this is secondary and is often grossly misused. People will talk of "Voltage dBs" without thinking what they mean and can easily fall down a hole at a later stage. Bringing dBs into the argument may be making things harder for some people but it is something that really needs to be treated rigorously.
Your specific examples of using a FET is just demonstrating that appropriate matching improves performance. Your FET is providing Power Gain - which is what the early stages of a receiver need - and making the best use of what you have been getting at the input. A transformer (whether or not you could actually build it is another matter) could have done a transformation of impedances - but it wouldn't necessarily have improved the noise situation, for instance.

The dear old emitter follower is definitely an Amplifier (with a capital A) yet its voltage gain is always a tad less than unity.
skeptic2
#15
Feb1-13, 04:56 PM
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Quote Quote by sophiecentaur View Post
This can be dismissed as a matter of semantics but I feel it's more important than that.
The word 'amplification' is used, loosely (sloppily, even) in both cases but it strictly means 'making a signal bigger' i.e. more powerful.
I think you are defining the word to fit your argument. Since the OP only indicted a concern with voltage and since the following definition does not specifically refer to power, I take it to mean making larger, greater or stronger the voltage. Speaking of semantics...

http://dictionary.reference.com/browse/amplify?s=t
am·pli·fy
[am-pluh-fahy] Show IPA verb, am·pli·fied, am·pli·fy·ing.
verb (used with object)
1.
to make larger, greater, or stronger; enlarge; extend.
2.
to expand in stating or describing, as by details or illustrations; clarify by expanding.
3.
Electricity . to increase the amplitude of; cause amplification in.
4.
Archaic. to exaggerate.
verb (used without object)
5.
to discourse at length; expatiate or expand one's remarks, speech, etc. (usually followed by on ): The preacher amplified on the theme of brotherly love.

We are not talking about power gain in this post, we are talking about voltage gain. Is not voltage gain defined as Vout/Vin?

There are applications where the voltage gain is important but power gain is not. Ironically given your statement, "Your FET is providing Power Gain - which is what the early stages of a receiver need" the receiver front end is one in which voltage gain is more important than power gain. This is because when stages are impedance matched, you lose 30% of the voltage between stages. If each succeeding stage in a receiver has a higher input impedance than the output impedance of the stage ahead of it, you lose less voltage between stages resulting in higher overall voltage gain.
sophiecentaur
#16
Feb1-13, 05:17 PM
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This argument could run and run but we all know that a transformer is not an amplifier, in any language. Voltage multiplication merely changes impedance. Equating a transformer to an amplifier is like equating a mechanical lever to a servo - it's only half the story.

Dictionary definitions of words that are used colloquially are not relevant to a specialist subject.

In the early stages of a receiver (designed to receive low level signals), the signal power needs to be brought above the local noise power as early as possible. Most receivers use some transformation to present the input signal at an appropriate impedance to suit the first stage amplifier (I think they refer to this as noise matching?). Merely transforming to a higher voltage is of no help to SNR whatsoever because that represents a higher noise resistance. The noise Power just depends upon the temperature of the equivalent input resistance and a good receiver attempts of limit significant noise contribution to the first stage only, when possible. It can only do this by true (power) Amplification and, of course, noise matching is used.

I agree that voltage gain is often the only thing that counts in specific applications but that is only in mid-level circuits. It is not relevant in input stages where low signal levels appear or in output stages where you really need some Power. My pernicketiness was just there in order to get the word 'amplification' into proper perspective. Transformers do not 'amplify', in any strict sense of the term; they may 'multiply voltages' but that's a different matter.
NascentOxygen
#17
Feb2-13, 07:57 AM
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Hi bukks,

Quote Quote by bukks bunny View Post
Hello friends.I was just wondering if a step up transformer can be used to amplify voltage signals like a transistor,as it step up input voltage at its output.?
A transformer can step up the voltage, but in EE this is not referred to as amplification. It is termed magnification. The word "amplification" is restricted to applications involving an active device, viz., an amplifier. The distinction may seem slight, but in practice it really isn't.
sophiecentaur
#18
Feb2-13, 05:06 PM
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Spot on.


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