On Lenz's law, Wikipedia says:

Faraday's law states that the EMF is also given by the rate of change of the magnetic flux where epsilon is the electromotive force (EMF) and \$\phi_B\$ is the magnetic flux.

$$\varepsilon = - \frac{-d \phi_B}{dt}$$

I want to produce this effect very strongly in a small coil (1cm^2 cross section max of the coil) for my project. It's not possible to have massive current carrying wires in a big coil using 240VAC from mains, and I don't want to start a fire either - so I'm thinking trying using a power amplifier such as OPA547T to amplify a very high HZ (e.g. 10MHz) signal from a signal generator (JDS-2900) using only a small current (e.g. 0.5A).

My electronics is pretty basic though, so was wondering if this is a viable and safe solution? Also is the OPA574T capable of this, or do I need to look for an amplifier with different characteristics in some way? Many thanks

  • \$\begingroup\$ The OPA547 can only produce 0.5 amps and virtually nothing at 10 MHz. It's maximum supply voltage is 60 volts too. \$\endgroup\$
    – Andy aka
    Oct 5, 2021 at 11:31
  • \$\begingroup\$ @Andyaka Thanks - can you explain a bit more how you know that? What amp characteristic do I need to look for to get this to work? \$\endgroup\$ Oct 5, 2021 at 11:33
  • \$\begingroup\$ You read the data sheet: ti.com/lit/ds/sbos056f/… \$\endgroup\$
    – Andy aka
    Oct 5, 2021 at 11:33
  • 1
    \$\begingroup\$ Maybe look at the schematics for a Metcal soldering iron. It pumps 50+ Watts at 13.56MHz \$\endgroup\$
    – Kartman
    Oct 5, 2021 at 11:34

1 Answer 1


I believe the salient characteritics of amplifier one needs to look for in this situation are bandwidth and slew rate which both contribute to the settling time of the output after a step change at the input - in my understanding, the slew rate is the rate of change for large voltage changes and the bandwidth is the maximum frequency it can operate with expected behaviour for small voltage changes -

"Electrically speaking, the frequency at which the signal gain is 1/sqrt(2) or 0.707 of the ideal value is the bandwidth of the op amp. This is the maximum frequency at which op amp can operate with expected behavior." Read more on this page

Opamp chosen was TLE2081CP.

As far as I've read, as long as one makes sure the coil wire can handle the amount of current passing through it, the fact that it's high frequency AC doesn't make it any more dangerous than the same current supplied in DC format.


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