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For my research purpose, I am planning to design one power amplifier (basically, a current amplifier) with the following specification-

  1. Frequency range: 0-100MHz (or at least 0-30MHz)
  2. Output voltage: 30Vpp
  3. Minimum output load: 3Amp
  4. The input current is expected to be very low as it will be feed from a simple function generator (max output current is not specified in the function generator manual, but I think, they should be less than 30mAmp)

Initially, I was planning to use an RF op-amp but later realized, none of the commercial op-amps can drive such high current. What would be the most optimized design for this circuit?

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  • \$\begingroup\$ Do you have a gain requirement, or is this a unity gain buffer? \$\endgroup\$
    – The Photon
    Jun 8, 2019 at 0:41
  • \$\begingroup\$ input current would be very low as it will be feed from a simple function generator (max output current is not specified in the function generator manual, but I think, they should be ~30mAmp) \$\endgroup\$ Jun 8, 2019 at 0:48
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    \$\begingroup\$ Amateur radio people build such devices all the time to act as as transmitters. You may want to look into these circuits \$\endgroup\$
    – user69795
    Jun 8, 2019 at 1:55
  • \$\begingroup\$ Could you please refer any exact reading material? I am a novice in this area. \$\endgroup\$ Jun 8, 2019 at 2:25
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    \$\begingroup\$ If your load solenoid is N=1000, then you can forget driving it with anything >100kHz \$\endgroup\$
    – Neil_UK
    Jun 8, 2019 at 5:39

1 Answer 1

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Narrowband solutions may be preferable, with PI-network output tuning to "match" into your inductor/solenoid load, and the PI filtering will reduce distortion and random noise that may confuse your research results. The amateur-radio people, for efficiency, may use class "C" on/off amplifiers, where PI-network filtering is required to meet harmonic interference restrictions; the "transmitters" have a 2-step process to change frequencies: at low power, tune the PI-network, then crank up the power. Given restrictions in radiated energy above 100KHz?, your 30 watt goal may have your local government investigating your research.

But if you want a broadband approach, something about like this

schematic

simulate this circuit – Schematic created using CircuitLab

Notice there is NO short-circuit protection. And this circuit is AC_coupled.

The power output may be easier, if the final NPN and PNP are large MOSFETS instead, with large Safe Operating Area. The capacitances of the MOSFETS will be a challenge to drive at 30MHz.

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