Four transistor/full bridge version of the Royer oscillator

Thread Starter


Joined Sep 16, 2011
For some time now, I have been trying to figure out what (in theory) would be the most efficient way transfer power across a transformer. Applications include high voltage power supplies and induction heaters. I have become very interested in the Royer oscillator and derivatives of it such as the "Push-Pull 2n3055 driver" mentioned here:
What bothers me about the Royer oscillator and its derivatives is that it uses two transistors to control two coils (center tapped) rather than four transistors to control one coil. I have a hunch that there exists a way to improve on the design using a full h bridge rather than a push-pull center tapped design.

I have been working on a driver, and I wanted some feedback (no pun intended) on how it might work and/or scale.

The design is not complete yet, but I was hoping it would at the very least convey where I was going with this. At best, this is going to be the design I build on by adding some protection for the transistors and driver.

I tried to make the picture as illustrative as possible despite the bad quality. Please let me know if/when you have trouble reading it and I will try to clarify. The driver relies on 4 pairs of op amps with their inputs crossed as seen here
Each pair of op amps controls one transistor. They all switch according to the voltage generated by the feedback coil F. I think I have the wiring displayed correctly, but the feed back coil outputs may need to be flipped.

The principle of operation (or at least the one I am shooting for) is as follows:
When most of the power is being transfered across the transformer and into the load across the secondary (could be anything from a spark gap to the work coil of an induction heater), minimum power is being sent through the feedback coil. However, when the oscillation at the primary is out of sink with the that of the secondary, the excess magnetic flux in the transformer core gets transfered into a voltage across the feedback coil which then causes the h bridge to switch. So, as I see it, the feedback coil acts as a device that measures impedance mismatch and controls the h bridge accordingly.

I could be completely wrong in both my theory and my circuit. I am still rather new to electronics and am learning the best I can.



Joined Sep 9, 2010
...when the oscillation at the primary is out of sink with the that of the secondary...
Out of synch? You mean a phase shift from primary to secondary? Determined how? Doesn't the shift depend on the inductance of the load?
...the excess magnetic flux in the transformer core gets transfered into a voltage across the feedback coil...
I'm no transformer expert, but I have studied and worked with this stuff a bit, and I have no idea what "excess flux" is.

Anyway, you might find a more useful response over in "General Electronics" or even "Homework Help". I think you need to nail down the theory of what you're doing before you go to build something. This forum leans heavily towards flashing LEDs, proposing over unity machines, solar battery chargers and the like.

Thread Starter


Joined Sep 16, 2011
Thanks for the feedback and advice. When I said "excess flux" I was picturing the primary inducing a magnetic flux through the secondary, and the secondary inducing a magnetic flux through the primary. When both of them are in phase I pictured the secondary's flux being absorbed by the primary and the primary's flux being absorbed by the secondary (absorbed=converted into power.) When they fall out of phase, there will be a large flux outside of the primary and secondary coils that I picture "leaking" into the feedback coil, which triggers the h bridge to switch direction.
Thanks for the response. I assume I did not do a good enough job of explaining what I was going for. I will try to explain better before at such point that I repost this in the general electronics forum.