HF Amplifier ideas

Discussion in 'The Projects Forum' started by DickCappels, Jul 16, 2012.

  1. DickCappels

    Thread Starter Moderator

    Aug 21, 2008
    2,664
    634
    A friend asked if I could recommend an amplifier circuit with which he intends to drive a Tesla coil in some experiments. I think this could be done with discrete components pretty easily, but I don't think he is eqiuipped to build and debug such a circuit. Thinking that an integrated or hybrid circuit would be easier for him to work with, and having searched around the web today, finding nothing, I am turning to those of you have a better idea of what kinds of integrated and hybrid solutions are out there. If an inexpensive pre-built amplifier is available, that would be even better.

    Here is what I think he needs:

    • Fixed gain of 10x to 20x
    • Output to 10V P-P
    • Frequency range (nearly) DC to 10 MHz, being pretty flat
    • Capable of supplying hundreds of milliamps
    • It must be linear to handle sine waves, some distortion is ok

    Any ideas? Thank you in advance for considering this problem.
     
    Last edited: Jul 16, 2012
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    It is not really an RF amplifier, but this opamp has the capability of 150 mA output and a bandwidth of over 200 Mhz.

    http://www.ti.com/product/LM7372

    You could place them as a bridge amplifier for the higher voltage output.

    Bertus
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    Not an expert, but it strikes me that an audio amp would cover the low frequency end pretty well.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,178
    1,799
    I'm no expert on Tesla coils, but I think driving one at high frequency is going to be very difficult. As you know the impedance of an inductor goes up with frequency. At sufficiently high frequencies the windings develop significant distributed capacitance and there will be a resonant tank circuit at some point that has the potential for great destruction. I could be wrong but I think most amplifiers are much happier with relatively flat load impedance.

    If you look at a typical audio setup you'll notice that the speakers and crossover networks are arranged so that the amplifier has less variability in impedance over the audio range.

    Do you even know what the impedance of the Tesla Coil is over the frequency range? Do you have a VNA to measure it?
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    Inductance should be easy to estimate reasonably well by calculation, and I recommend doing that (or measuring it) before considering any solution.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,178
    1,799
    That is true, but the "load" as seen by the amplifier is what will determine if it will do what you want it to do. Most Tesla coil circuits I have seen are powered from the mains via a transformer. There are very few amplifiers that can duplicate the behavior of the mains.

    http://en.wikipedia.org/wiki/Tesla_coil

    Scroll down to "Applications"
     
  7. DickCappels

    Thread Starter Moderator

    Aug 21, 2008
    2,664
    634
    Thank you, Burtus. The LM7372 looks like the right amplifier, at least for him to begin testing.

    Wayneh and Papabravo, he isn't going to be throwing sparks as far as I know, just looking for some subtle effects. I am counting on resonance to reduce the drive requirements, at least at that frequency.

    I think the problem is solved, for now at least, thanks to you all.
     
Loading...