12 MHz oscillator

Discussion in 'Wireless & RF Design' started by Janis59, May 16, 2018.

  1. Janis59

    Thread Starter Active Member

    Aug 21, 2017
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    (Moderator's note: This thread was started by moving posts #1 through #13 from the following thread: https://forum.allaboutcircuits.com/threads/12-mhz-oscillator-with-a-voltage-range-120v.148686/)


    Everyday I am producing 40-100 MHz generators with falling characteristic slope (=current source=serial resonance) of ca 2000-5000V at 100W...200W...1000W. Their Vcc is between 24 and 30 V DC.
    If Your demands stay ever near, You may ask me about circuitry and grand stoppers. But if Your interests are hard output slope (=voltage source=parallel resonance) then I cannot help very much as only to refer to ANY small spiral-like incandescent lamp circuitry. Find one dead, go to the place where EPA inspectors dont see You, and extract the transistors. Every contain the 400V (CE) or 600V (BC) pair, most often it stays CD13003 (TO-220) or 3DD4202BD (TO-92). Both has F(T)=4 MHz.
    From higher power devices still at about 5 USD pricing stays 600V 15A and declared 40 MHz however capable for near 100 MHz the ixfh42n60p3 and slightly less powerful but twice faster apt6038bll for about 10 USD.
     
    Last edited by a moderator: May 21, 2018
  2. Bordodynov

    Well-Known Member

    May 20, 2015
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    See
    2018-05-16_15-22-49.png
     
  3. Janis59

    Thread Starter Active Member

    Aug 21, 2017
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    RE: Bordodyunov
    Why so sophisticated? Let elementary reduced Clapp instead!
    The IXFX42N60 drain to radiator mass. Source to few turn (~10) coil of 1,5mm wire on cork cylinder diam 25-30 mm, the coil to resistor of ca 0,1...0,3 Ohm going to minus terminal.
    Gate to tank capacitor, tank capacitor to tank coil, tank coil to radiator mass. This capacitor must be qualified for at least 5 kV and 10 Amp, and adjusted for no much more than 40 MHz, however ultimatively no more than 85 MHz. Radiator with fan must be about 200W, from pentium series PC is too small.
    The other wire from gate goes to delinkage coil (without of it the potentiometer will evaporate in seconds), about 10 uH on ferrite rod, put in metal box, the outside is connected to potentiometer middle between +12V and gnd. The +12V must be produced not by 7812 what is hardly suffering the madness under RF induction, but by means of most slowest npn bjt what is possible to find on planet. For me very well serves a soviet kT805 - slow, insensitive, costs dollar a full box. The Zener in it`s entrance, of course.
    Thus, the 5 kV are warranted, 10 Amps are warranted, 200W are warranted. To the 6 MHz probably power will be even better.
    Why it is generating? Thats a good question, just inner parasyte Cgs serves as Clapp positive loop, therefore that inductance in source. Resistor there is only for give it a minimum thermal stability.
    Tank capacitor? At such reactive power to find the Vishay capacitor under some 3000...6000 USD is not much realistic, thus one way working well up to 50...100W is to mount plethora of SMD 10 pF 2 kV in series - parallel. For example, 20-40 pieces parallel twigs each of three in series. Over the 100W this is not working, all xplodes. Then the way out is Rogers inc Duroid(TM) teflon-base PCB having around 2 pF/cm2. It may be used up to 100A/dm2. My experience of utilizing the ordinary glass-textollite FR4 and FR2 gives 300-600C temperature in seconds. The tan(fi) of their is far too large, but at 6 MHz I have no experimental data - may try to play with it.
    Negative sides - none, except that mass is positive and feed input is negative. Max voltage theoretically ought be 40V (what is permissible U(g max)), but factually over 27V is dangerous, and over 30V is clearly dangerous. Anyway, the RF 5kV p-p in exit is very realistic result, but if coil is rather thick-wired and silvered then even 10 kV.
     
  4. Janis59

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    Aug 21, 2017
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    RE: Papabravo: ""And all transistors of type bjt"".
    The circuit is capable (and well) work even at npn-type bjt.
    Just in such case Yourself find the candidate, and probably, between the B and E will be needed a certain small surplus capacitor, 100pF or 200. Or not needed.
     
  5. Janis59

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    Aug 21, 2017
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    RE: Bordodyunov
    And more over, Your circuit is just the half of patented by more than 2 US patents about generator for QMS ICP plasma torch. And those all I have examined very much, all are false. Without of microprocessor regulation they are mostly hopeless.
     
  6. Bordodynov

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    May 20, 2015
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    I decided to have some fun and drew this outline.
    I doubt that the author of this topic will use this circuit solution.But he is to blame.You need a more complete description of the requirements for the device.I have studied very little patents, especially American ones.I'm just drawing schemes and the rest does not bother me.I met an eccentric who needed a high-frequency oscillator.He took a powerful transistor and gave him an initial current resistor.He twisted the lead wires and it worked!
     
  7. Janis59

    Thread Starter Active Member

    Aug 21, 2017
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    So it is, rather frequently in this World full of badly illogic things.

    Even the fence mare will oscillate when it is unwelcome, but when the oscillation is the very aim, then every even best circuit is going to the teeth.

    Absolutely agree that circuitry for say heterodyne oscillator is sth far different to circuit of induction heating oscillator, or aluminium welding initiator generator. Designer MUST know the aim of circuit, undoubtly.
     
  8. Janis59

    Thread Starter Active Member

    Aug 21, 2017
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    By the way, I like the solve of bias in Your circuit. Thanks, I shall hang it on the wall for better memorize and use when need.

    However the capacitative divider 1:100 seems bit weak. From 30 V Vcc on the coil may happen many kV, eg 3kV 5 kV or even rarely 10 kV. That would give a sure kaput for transistors. At least in my case I have fully capitulated of hope to measure by similar method the voltage on my tank. The error is ca 300% or more. Each cap has own parasythic inductance, ESR and tan(fi) etc etc So, the divider NEVER is so `pure` as one may draw, but rather damn complicated, and this is unavoidable problem.

    When I first searched for the QMS torch patents, I throw the circuit of transformer linked loops with disgust, but after few years I returned to them back as only alone what are trustable and stable. Just if to bit calculate the crosslinked inductances, may cach that enough linking may be gained by just ONE turn at one inch off the straight lead part of main tank. Just provide the pcb based one turn `coil` on the oval screw-holes, and adjusting the distance to tank may get the coupling factor whatever want. So, from that very moment I changed a religion from believers of capacitative coupling toward believers of inductive coupling. :)
     
    Last edited: May 21, 2018
  9. Janis59

    Thread Starter Active Member

    Aug 21, 2017
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    RE: Papabravo
    We still use that vacuum tube multivib circs elaborated at early 60ies at us, on basis of GU-50, GU32 etc. Still operable if once every five years to shift the tube. BUT, the size. BUT, the unease of feeding (filament, anode....).
    However, it are unkillable. Often our technicians make a full short of the tank coil... then anode becomes sun-colour at few seconds. By that is clearly indicated sth went wrong, they take it off and put in `to repair` queue. Very rarely there the tube is damaged, if only short was not minutes long. And if to immaginate that those will be the very solely RF electronics capable to survive the Putin`s nuclear button pushing (I refer to his phrase "Why You think we need any World if in it will not proudly standing the Russia").....
     
    Last edited: May 21, 2018
  10. Bordodynov

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    May 20, 2015
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    Janis59, I solved the inductance problem.
    See 2018-05-17_15-29-11.png
    2018-05-17_15-58-15.png
     
    Last edited: May 17, 2018
    Danko likes this.
  11. Janis59

    Thread Starter Active Member

    Aug 21, 2017
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    Wow!
    But I dont recognize what is T1. One-turn transformer??

    By the way, if this circuit will work well (I shall test it obligeously), it may create the small `disruptive innovation` in ICP plasma devices power supplies technique.

    Just this moment all devices are fed by serial tank to get voltage high enough for ignition (1...2 kV). But this circuit, when some 1,2 or 1,8 kV transistors are applied, may work in `oldy goody school` style with parallel tank, giving hardly larger current in plasma, while ignition is determined by Vcc.
     
    Last edited: May 21, 2018
  12. Bordodynov

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    May 20, 2015
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    T1 - 50 Ohmic cable (about 4 meters long), shorted at the end. It is a quarter-wave resonator. Advantage - less electromagnetic interference! For a miniature cable can be rolled into the bay.
    This device is low-power. Tens of milliwatts are scattered on transistors.
     
  13. Janis59

    Thread Starter Active Member

    Aug 21, 2017
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    Ahoi! Thanks.
    1) my case the f>108,48 MHz (8th harmonic of 13,56) or at least f<81.6 MHz (6th), it means the length of 75 cm or about
    2) my case I must scan the RF ultrahigh voltage choices for carbide transistors
    3) my case everything under 10...20 Amperes are neglected.
    So, the principle is sth worth indeed, not a concreted nominals.

    4) However, the magnetic field in the coil is the thing what I am looking for. I wonder if really I need a 1/4 wave resonator if that may be the work coil of my RF torch.
     
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