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Distorted Sine output from Transformer

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jimmykk

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Hi

I am using an amplifier(LT1210) with +-15V Supply and its output is connected to a transformer RM10 core N97 with 9:150 step up ratio and its output has to be connected to various
piezoelectric transducers in the range 40 to 300khz and impedances varying from 20 to 2.5k Ohm.
The problem is i cant amplify my signal as much as i want to as the sine wave gets distorted and also i have to connect a resistor between amplifier and transformer to make this circuit work.
I would like to send so much power as i can to the transducers so that receiver signal can be increased.
Input into Amplifier: Sine wave:2 to 4V(40 to 300khz)
Thanks
 

KlausST

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Hi,

My first idea: did you check the output current of the amplifier?

***
piezoelectric transducers in the range 40 to 300khz and impedances varying from 20 to 2.5k Ohm.
What exactly does this mean?
40 kHz ... 300 kHz?
20 Ohms ... 2.5 kOhms?

***
A 9:150 transformer will transform the load impedance to the primary side: ZL_P = Z_LS / 278

Thus 2.5kOhms will become 9 Ohms (transformer impedance not included)

****

Are you sure the transformer does not saturate?

Klaus
 

jimmykk

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<<My first idea: did you check the output current of the amplifier?>>

I didn't measured it but it is supposed to deliver between 1-2A

***

What exactly does this mean?
40 kHz ... 300 kHz?
Basically its the measuring bandwidth of various transducers. Some of them have 40 to 160khz while others have 100 to 400Khz
20 Ohms ... 2.5 kOhms?
and their impedance changes and follows a curve e.g. a 40 to 160khz tranducers has impedance from 80 to 900 ohms
***
A 9:150 transformer will transform the load impedance to the primary side: ZL_P = Z_LS / 278

Thus 2.5kOhms will become 9 Ohms (transformer impedance not included)
Yeah so the Zprim is negligible but still i cant run the circuit if i directly connect the outpuut of the amplifier to the primary of the transformer.
can you explain transformer impedance calculation

****

Are you sure the transformer does not saturate?
All i see is it produces distorted outputs around 40khz and as the frequency increases the signal improves also.
Klaus[/QUOTE]
 

KlausST

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Hi,

I didn't measured it but it is supposed to deliver between 1-2A
"Supposed" values are useless, especially when there is a problem.
--> measure it.
"Deliver" means the source side. But (for undistorted waveforms) the current should be determined by the load.

Please use QUOTE tags. (Buton with speech balloon).
What exactly does this mean?
40 kHz ... 300 kHz?
20 Ohms ... 2.5 kOhms?
Sorry, I just wanted to know the "units of the left side values"
Is it 40 Hz or 40 kHz?
Is it 20 Ohms or 20 kOhms?

Mind that the frequency information of transducers as well as transformers usually are for pure sinewave, thus you need to tell us is you use another waveform.

Yeah so the Zprim is negligible
How can you be sure about this?

but still i cant run the circuit if i directly connect the outpuut of the amplifier to the primary of the transformer.
If transducer impedance is 20 Ohms, then this will be translated to 0.072Ohms.

can you explain transformer impedance calculation
--> https://en.m.wikipedia.org/wiki/Transformer

Klaus
 

jimmykk

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The values are 40khz to 400khz and 20ohm to 2500ohms.
I am using pure sine wave as input.
I ran a test with a transducer with frequency range 100khz to 400khz and its impedance changes from 20 ohms to 150 ohms in that frequency range with two peaks around 120 ohm.
when i gave 1Vpp sine input to op amp with Gain=9 and +-15v supply, and this time i did not used any resistor between op amp and transformer, i got distorted output(@100khz) over transducer as:-100khz.PNG
 

KlausST

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Hi,

Why do you waste your time with giving the same information again and again?

I´ll come back if you have the scope picture of the current...

Klaus
 

Electronics_chaitanya

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Hello..

Try to put capacitor between Transformer and amplifier.
Probably 105 (1uF) High current MFR can do your work by eliminating DC component which may cause saturation of cores.

Look i am not an expert in case of megnatics but you should try it once.


Regards
 

jimmykk

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Thanks for suggestion..... but i am not sure how adding a capacitor in series between amp and transformer would have an influence on the
interested frequencies from 40khz to 400/500khz. won't it act as a filter and eventually, would a simple 1uf ceramic would do the job
 

Electronics_chaitanya

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Hello

at this frequencies capacitive impedance is low so i think you work may be done.

If you are in country where 2MFD film capacitor easily available then try with 2uF. though 1 uF also performs well but don't use polarized capacitor obviously.

Moreover if your frequency range is from 40Hz to 400Khz then issue of capacitive filtering may rise but at 40Khz to 40Khz it works well. I have tried it for my IGBT gate driver transformer before some years.


Though for high current this config may unsuitable...you need to use capacitor bank for high current.
 

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