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Function of capacitors in Royer oscillator

FrostyJams

Mar 6, 2022
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So I have a slightly modified Royer oscillator circuit that is driving a high voltage RF output for a frequency based medical device. The transformer has a center tapped primary coil with a center tapped feedback coil driving it so that the system runs at the resonant frequency of the saturated coil. I am not a circuit designer but I understand the basics of how this circuit works. I have begun to tinker with the value of the capacitors @ C8 and C9 and notice that it does change sensation of the output signal on our wand but it doesn't seem to be changing the frequency or the waveform of the output, which is a sine wave, or the waveform of the feedback coil. So I am wondering if anyone can tell me what changing these capacitors should affect so I can look for it and hopefully be able to optimize the output. during my "tuning" I have used capacitor values for C8 and C9 ranging from 30nF to 147nF and found that 139nF "feels" best but I would like to understand more about parameter what I am actually changing. I am posting some scope files with various values in C8 and C9 with the Yellow and Red waveforms measured at the corresponding scope probes located at the Yellow and Red circles on the schematic. The scope files have 30nF, 50nF and 100nF values installed for each capture but the feedback wave in Red basically doesn't change. The output to the primary wave in Red has a slight phase shift but doesn't really cause a change in the feedback waveform. Thanks in advance for your input.Royer Oscillator.jpg V2.2 15kHz C8_9 30nF R2_3 33 Ohm R5 100 Ohm Power L4.png V2.2 15kHz C8_9 50nF R2_3 33 Ohm R5 100 Ohm Power L4.png V2.2 15kHz C8_9 100nF R2_3 33 Ohm R5 100 Ohm Power L4.png
 

AnalogKid

Jun 10, 2015
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The conditions of each scope shot are the same: 30 nF and 330 ohms.

ak
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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So I have a slightly modified Royer oscillator circuit that is driving a high voltage RF output for a frequency based medical device.
What does this mean? What is a "slightly modified Royer oscillator circuit" and where can we find a schematic and parts list for an un-modified Royer oscillator, although I suppose we could look up George H. Royer's 1954 patent US2783384A? What is the RF output frequency? Your o'scope wave forms appear to indicate a period of 80 microseconds for the oscillations. That is a frequency of only 12,500 Hertz, which hardly qualifies as radio frequency output. And what is a "frequency based medical device?" Do you plan on getting FDA approval for this "medical device?"

The beginning of this thread sounds a lot like "woo woo science" which is forbidden here. You stated:

it does change sensation of the output signal on our wand
Wow! So exactly what sensation do you want, and how do you want to change the sensation you have now? Is this project in any way related to the use of so-called violet wands?

And what, exactly, is your question for this forum? We love to help!
 

FrostyJams

Mar 6, 2022
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What does this mean? What is a "slightly modified Royer oscillator circuit" and where can we find a schematic and parts list for an un-modified Royer oscillator, although I suppose we could look up George H. Royer's 1954 patent US2783384A? What is the RF output frequency? Your o'scope wave forms appear to indicate a period of 80 microseconds for the oscillations. That is a frequency of only 12,500 Hertz, which hardly qualifies as radio frequency output. And what is a "frequency based medical device?" Do you plan on getting FDA approval for this "medical device?"

The beginning of this thread sounds a lot like "woo woo science" which is forbidden here. You stated:


Wow! So exactly what sensation do you want, and how do you want to change the sensation you have now? Is this project in any way related to the use of so-called violet wands?

And what, exactly, is your question for this forum? We love to help!

Thank you for your reply hevans1944, yes it is a device based off of Tesla's Violet Ray Machine but it utilizes the feedback coil to detect varying capacitance on the output which alters the frequency of the entire system dynamically while it is running, this is a desired operation of our circuit. A standard Royer oscillator does not work in our application so it is not referenced here. The device does run in the audible frequency range which is technically VLF (very low frequency). We are looking to create our output to be as close to a natural sine wave as possible while maintaining the frequency variability described above.

My question specifically is what am I changing when I adjust the capacitance of the circuit, I don't see much changing in the waveforms of my scope but it is changing the output sensation. "Feeling" a difference is obviously not scientific so I am trying to understand theoretically what should be happening so we can optimize the circuit accordingly.
 

AnalogKid

Jun 10, 2015
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Please re-post the photos with the correct identifiers. It should help the discussion if we know what we are looking at.

We know nothing about the design or construction of your transformer, but the circuit you posted is not a Tesla coil. In a Royer power oscillator, the transformer is not resonant. With the right construction it can produce a very high output voltage, but the vast majority of high voltage conversion circuits are not resonant, and not Tesla coils.

In your circuit, each R-C combination is a delay circuit that does two things. First, they affect output frequency. Second, they prevent cross-conduction, a case when both transistors are on at the same time. Depending on the speed of the transistors and the inductance of the transformer, sometimes a diode is added across each resistor to guarantee that each transistor turns off faster than the other one turns on.

Generally speaking, changing the capacitors together (maintaining equal but changing values) will affect the output frequency more than the wave shape. This depends greatly on the transformer winding inductances and mutual inductances. Changing one capacitor's value with respect to the other affects the output wave shape more than keeping them equal, by making the output waveform non-symmetrical. The same is true about the resistors, but changing them also affects the base current driving the transistors, which changes their saturation characteristics, which adds another layer of complexity to what is going on inside the transformer.

Keeping one capacitor or resistor constant while changing the other has the largest affect on the output with the least effort.

A varying capacitance at the output can reflect back through the core and affect the operating frequency, but it takes a large change. You don't say what the required output voltage and current are, so what you want might not be possible. The human body presents a very small capacitive load on a circuit, especially when not in direct contact.

NOTE: No warranties expressed or implied. Among other bad things, this circuit can fry a pacemaker.

ak
 

FrostyJams

Mar 6, 2022
5
Joined
Mar 6, 2022
Messages
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Please re-post the photos with the correct identifiers. It should help the discussion if we know what we are looking at.

We know nothing about the design or construction of your transformer, but the circuit you posted is not a Tesla coil. In a Royer power oscillator, the transformer is not resonant. With the right construction it can produce a very high output voltage, but the vast majority of high voltage conversion circuits are not resonant, and not Tesla coils.

In your circuit, each R-C combination is a delay circuit that does two things. First, they affect output frequency. Second, they prevent cross-conduction, a case when both transistors are on at the same time. Depending on the speed of the transistors and the inductance of the transformer, sometimes a diode is added across each resistor to guarantee that each transistor turns off faster than the other one turns on.

Generally speaking, changing the capacitors together (maintaining equal but changing values) will affect the output frequency more than the wave shape. This depends greatly on the transformer winding inductances and mutual inductances. Changing one capacitor's value with respect to the other affects the output wave shape more than keeping them equal, by making the output waveform non-symmetrical. The same is true about the resistors, but changing them also affects the base current driving the transistors, which changes their saturation characteristics, which adds another layer of complexity to what is going on inside the transformer.

Keeping one capacitor or resistor constant while changing the other has the largest affect on the output with the least effort.

A varying capacitance at the output can reflect back through the core and affect the operating frequency, but it takes a large change. You don't say what the required output voltage and current are, so what you want might not be possible. The human body presents a very small capacitive load on a circuit, especially when not in direct contact.

NOTE: No warranties expressed or implied. Among other bad things, this circuit can fry a pacemaker.

ak
Thank you for the explanation Analog, the changes in cap values are done in pairs but don't make really much change in the output frequency as you correctly describe. I have attached the specifications for the transformer we are using as well as updated scope files. The pink overlay on the second (50nF) and third (100nF) files is the (30nF) capture for comparison.

Our device output wand makes direct skin contact with the patient and does represent a large change in the frequency, up to 25% off our base frequency of 13.9kHz with no contact down to as low as 9.9kHz with full wand contact. I concur with the pacemaker observation, we do not allow people with pacemakers to use the device.

We are experimenting with different options on the oscillator to try to get the most natural sine wave under load as we believe it will be more effective. We have had some suggestions of adding reverse diodes across the B-E of the transistors instead of the caps or caps across C-E of the transistors. I don't quite understand how these would affect the circuit, do you have an opinion on wither option. We have also been told that a cap across the Primary coil at P1-P3 will help but again I don't understand how this would affect the circuit. I am trying to learn how these modifications will change our output without having to trial and error different components endlessly.

Transformer Model (1).png Transformer_GAP0.png V2.2 15kHz C8_9 30nF R2_3 30 Ohm R5 100 Ohm Power L4.png V2.2 15kHz C8_9 50nF R2_3 33 Ohm R5 100 Ohm Power L4.png V2.2 15kHz C8_9 100nF R2_3 33 Ohm R5 100 Ohm Power L4.png
 

Attachments

  • Transformer Model (1).pdf
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  • Transformer_GAP0.5_191018.pdf
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  • V2.2 15kHz C8_9 30nF R2_3 30 Ohm R5 100 Ohm Power L4.png
    V2.2 15kHz C8_9 30nF R2_3 30 Ohm R5 100 Ohm Power L4.png
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  • V2.2 15kHz C8_9 50nF R2_3 33 Ohm R5 100 Ohm Power L4.png
    V2.2 15kHz C8_9 50nF R2_3 33 Ohm R5 100 Ohm Power L4.png
    20.5 KB · Views: 2
  • V2.2 15kHz C8_9 100nF R2_3 33 Ohm R5 100 Ohm Power L4.png
    V2.2 15kHz C8_9 100nF R2_3 33 Ohm R5 100 Ohm Power L4.png
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