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Registered Member #4650
Joined: Sat Apr 28 2012, 04:29PM
Location:
Posts: 3
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. 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.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi, Just as an inspiration, I built this circuit to drive a Tesla coil, it kind of worked but didn't like oscillating at 200 kHz too much (it worked as expected but too much heat in the transistors). It is a full bridge version of the "ZVS" driver. Maybe it could work well for your transformer at lower frequencies. You can downrate the unnecesarily overrated components for your application.
Registered Member #4650
Joined: Sat Apr 28 2012, 04:29PM
Location:
Posts: 3
Thanks a lot! I have actually spent quite a bit of time looking for something like this! I see you added capacitors across the collectors and emitters of the transistors as you did in the "improved single transistor flyback driver" thread You also seem to have added quite a few other things such as capacitors in parallel with diodes (I imagine that would soften switching.) If you get a chance, it would help if you could give a quick rundown of the how some of the key components interact--so I know which parts are essential to the theory of operation and which parts are there to make it practical. Example: transistors are the switches of the h bridge while zener diodes keep them from being destroyed. This gives helps me understand the "main idea" of the circuit, then piece together how you modified it to make it work.
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Four transistor/full bridge version of the Royer oscillator
