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  1. #1
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    Toroid Coil Design and Implementation

    I would like to clarify a few things

    I have this circuits. Yes it si any RF PA with MOSFET.

    The first question how to calculate the size of the coil L2?
    Is this approach correct?
    L2 with Ciss in IRF510 make resonant circuits on working frequency. If yes
    Ciss on gate Threshold Voltage 3.5V is about 220pF
    f is 13,56MHz and resonant L is 626nH not 570nH
    Second option id simple L2 only set impedance of source on 50Ohm i.e. is supposed to be Xl=50 L2=587nH.

    How is it?

    Will have a second question about choosing the size and material of the toroids, but it will be clear what the size of L2 is

    Click image for larger version. 

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    Click image for larger version. 

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  2. #2
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    Re: Toroid Coil Design and Implementation

    The LC network needs a properly-selected ohmic resistance somewhere. Otherwise it won't do a proper job of shaping a square wave into a sine.

    Your schematic has two sections where the incoming square wave might possibly get shaped into a sine.
    Is it the input network?
    Or the output stage?

    By the way, since you have 20mA available to drive an LC network, it provides a method to convert 5V pulses into sine waves at 25 V output amplitude. There is no need for a mosfet or transistor, nor even a power supply.



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  3. #3
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    Re: Toroid Coil Design and Implementation

    for clarification.
    Clock source is pierce oscillator with one inverter from 74HC04 and other (5) inverter parallel is used as power driver of the circuits on the schematic that is, they are connected to L2. 74HC04 is powered 5.8V. 20mA was meant as max output current for 5.5V, not as output current into this load.
    schematic with IRF510 in the picture is first amplification phase in two transistor amplifer and it only wakes the power output transistor. Actually works by 25Ohm 6W resistor parallel with Ciss output MOSFET about 1900pF. Yes. transistor Q2 not works with +12V , but with +24V on L1 is in real DC +24V.

    However, I still do not know how to calculate the size of L2 and whether Cis C resonant or just define the resistance to charge C? Yes i saw similar wiring where instead of L2 was 5-10W Ohmic resistor, but her is relatively expensive toroids inductor and it must have a reason and somehow it has to go to calculate its value.



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