# flyback transformer circuit alternatives?

#### mdidomenico

Joined Mar 3, 2019
18
i'm new at this so my terminology and understanding could be wildly incorrect.

if you look at the attached diagram (which is incomplete), I'm looking at a reference circuit design that uses a flyback transformer to step up the voltage and convert a square wave into a sine wave. that description may or may not be accurate.

the transformer in this configuration is difficult to source. the reference diagram i have is using a custom wound version. is there an alternative method which could alleviate the transformer? preferably using components i can readily source, even if it means a less efficient design?

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#### DickCappels

Joined Aug 21, 2008
5,943
First of all that circuit ill probably not give much of an output because the diodes will block current in both directions.
Do you really need a sine wave on the output? Can you further describe your goal -the voltages and currents involved, the nature of the load, and things like that?

#### mdidomenico

Joined Mar 3, 2019
18
My understanding as it was described to me is; that the square waves come from a pair of mosfets that charge the transformer in a push-pull fashion, which then drives the transformer from +15V to something like 200Vpp and the diodes rectify it into a sine wave. i could be completely wrong though. the load after the diodes is a piezo-electric transducer

#### AlbertHall

Joined Jun 4, 2014
8,523
The diodes as drawn won't block or rectify anything.
When the transformer output is positive D1 and D3 will conduct and feed the voltage to the output. When the voltage is negative D2 and D4 will conduct and again feed the transformer voltage to the output. The output will be the same as the transformer voltage less about 1.5V for the forward diode voltage.

#### DickCappels

Joined Aug 21, 2008
5,943
How about dropping R1 and D1-D4?

If your transducer has sufficient Q factor the response would nearly the same with a square wave as it would with a sine.

@AlbertHall thank you for correcting my mis-statement about the doides.

#### mvas

Joined Jun 19, 2017
538
My understanding as it was described to me is; that the square waves come from a pair of mosfets that charge the transformer in a push-pull fashion, which then drives the transformer from +15V to something like 200Vpp and the diodes rectify it into a sine wave. i could be completely wrong though. the load after the diodes is a piezo-electric transducer
Diodes do not "... rectify into a Sine Wave ..."

Are you really trying to make an AC Sine Wave output at the Transformer's Secondary?

Input Voltage = 15 Volts DC ?
Input Amps = ? amps
Output Voltage = 200 Volts AC peak-to-peak ( so like 70 volts AC RMS ) ?
Output amps = ? amps
Frequency of the Square Wave = ? hz ( and is it fixed or variable ? )
Duty Cycle = ? ( and is it fixed or variable ? )

#### mdidomenico

Joined Mar 3, 2019
18
Diodes do not "... rectify into a Sine Wave ..."
Are you really trying to make an AC Sine Wave output at the Transformer's Secondary?
Input Voltage = 15 Volts DC ?
Input Amps = ? amps
Output Voltage = 200 Volts AC peak-to-peak ( so like 70 volts AC RMS ) ?
Output amps = ? amps
Frequency of the Square Wave = ? hz ( and is it fixed or variable ? )
Duty Cycle = ? ( and is it fixed or variable ? )
yes, i understand about the diodes now. like i said i'm new at this...

the input and output amps i don't know, it's probably very low though like mA ranges
the square wave is 200khz
Duty cycle is 50% fixed

I'm not intentionally trying to make a sine wave on the secondary, I'd like to understand how it gets there though. i think, but probably incorrectly, since one of the square waves is inverse, that the transformer some how combines the two square together into a sine on the secondary

#### mvas

Joined Jun 19, 2017
538
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#### DickCappels

Joined Aug 21, 2008
5,943
Since both halves of the windings are magnetically coulped and in series you can view the output as a single square wave.

It may be that the transformer has a high impedance (perhaps because of leakage inductance) and the resonator filters out the harmonics, resulting im a pretty nice sine wave.

#### mvas

Joined Jun 19, 2017
538
I'm looking at a reference circuit design that uses a flyback transformer to step up the voltage and convert a square wave into a sine wave.
Please, attach the URL of the Web Page showing a Flyback Transformer that converts a Square Wave into a Sine Wave ...

Joined Feb 20, 2016
3,080
I wonder if you are using the term "Sine Wave" as a replacement for AC (Alternating Current)?
The switched square wave on the primary of the transformer will produce an AC square wave on the secondary (ignoring ringing and transients). This square wave can be filtered to give a sine wave if needed, or the transformer resonated but a square wave will probably run your transducer ok.

#### mdidomenico

Joined Mar 3, 2019
18
I wonder if you are using the term "Sine Wave" as a replacement for AC (Alternating Current)? The switched square wave on the primary of the transformer will produce an AC square wave on the secondary (ignoring ringing and transients). This square wave can be filtered to give a sine wave if needed, or the transformer resonated but a square wave will probably run your transducer ok.
that's certainly possible, as i said i probably have the terminology wrong.

the device in question is this: http://airmartechnology.com/uploads/AirPDF/T1.pdf
they sent me the schematic's for the board, but i don't have explicit permission to share them on the web.

when i look at the resulting waveform with an oscilloscope it looks like a damped sine wave, but perhaps it's just a damped AC wave. which if true and you could drive the transducer with a square wave, i wonder why they went through all the trouble of generating the AC wave. unless that's just an artifact of the method they chose to drive the signal up to ~300vpp

#### mvas

Joined Jun 19, 2017
538
that's certainly possible, as i said i probably have the terminology wrong.

the device in question is this: http://airmartechnology.com/uploads/AirPDF/T1.pdf
they sent me the schematic's for the board, but i don't have explicit permission to share them on the web.

when i look at the resulting waveform with an oscilloscope it looks like a damped sine wave, but perhaps it's just a damped AC wave. which if true and you could drive the transducer with a square wave, i wonder why they went through all the trouble of generating the AC wave. unless that's just an artifact of the method they chose to drive the signal up to ~300vpp
Can you use your cell phone to take a photo of your "Damped Sine Wave" and then post image ?
"Damped" meaning the tops and bottoms of the sine waves are clipped?

So, you want to build an "inverter" circuit that is similar to the " ... Developer’s Module for Evaluation of AIRDUCER Transducers ..." ?
This Developer's Module allows you to:
a) change the amplitude
b) change the pulse width
c) change the frequency

Do you need the above functionality or is "Fixed Frequency + Fixed Pulse Width + Fixed Amplitude" OK ?

Can you provide URL link to the Web Page of the exact Transducer Model # that you are going to power with this inverter?
http://airmartechnology.com/productinfo.html?category=AT&name=Air Ranging Transducers

Example: At 100 Volts RMS and 500 Ohms load you will need approx 200 ma.
The Apparent Power might be much higher if the Transducer has a high capacitance.
Some Transducers may need a precise frequency.
Impedance matching / tuning, might be critical.
A High Voltage, Higher Frequency, Class D or Class E type Audio Amplifier might be what the Mfr uses?

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